Polymyositis (Adult)

1. Overview

Polymyositis (PM) is a rare, chronic autoimmune inflammatory myopathy characterized by symmetric proximal muscle weakness without the cutaneous manifestations seen in dermatomyositis. It represents one of the idiopathic inflammatory myopathies (IIM), a heterogeneous group of autoimmune conditions affecting skeletal muscle. [1]

The condition primarily affects adults, with peak onset between 40-60 years of age, and demonstrates a 2:1 female predominance. The hallmark presentation involves insidious onset of proximal muscle weakness developing over weeks to months, with patients typically reporting difficulty rising from chairs, climbing stairs, or lifting objects overhead. Unlike dermatomyositis, polymyositis lacks characteristic skin findings such as heliotrope rash or Gottron's papules, making the distinction critical for diagnosis and classification. [2]

Polymyositis has significant clinical importance due to its association with serious extramuscular complications, particularly interstitial lung disease (ILD) in 30-40% of cases, and malignancy in 10-25% of patients, necessitating comprehensive screening and long-term surveillance. [3,4] The condition responds to immunosuppressive therapy in 70-80% of cases, though some patients with specific autoantibodies (particularly anti-signal recognition particle, anti-SRP) may demonstrate treatment-resistant disease requiring aggressive multimodal therapy. [5]

2. Epidemiology

Incidence and Prevalence

Polymyositis is a rare autoimmune condition with an estimated incidence of 1-8 per million person-years and prevalence of 5-10 per 100,000 population. [6] However, true polymyositis may be rarer than previously thought, as modern diagnostic criteria and recognition of other inflammatory myopathies (particularly inclusion body myositis and immune-mediated necrotizing myopathy) have led to reclassification of many cases historically labeled as polymyositis. [7]

Demographics and Risk Factors

Age Distribution: Polymyositis primarily affects adults in midlife, with peak incidence in the 5th and 6th decades. Unlike dermatomyositis, which has a bimodal distribution affecting children and adults, polymyositis is predominantly an adult-onset disease. Onset before age 18 is extremely rare, and such cases should prompt consideration of alternative diagnoses such as juvenile dermatomyositis or muscular dystrophy. [8]

Sex and Ethnicity: Women are affected approximately twice as frequently as men. Some studies suggest higher incidence in African American populations compared to Caucasians, though data are limited. [9]

Genetic Susceptibility: HLA associations have been identified, particularly HLA-DRB103:01 (DR3) and HLA-DQA105:01, which confer increased risk for polymyositis and are also associated with specific myositis-associated antibodies and interstitial lung disease. [10]

Associated Conditions

Temporal Trends

Recent population-based studies suggest the incidence of diagnosed polymyositis has decreased over the past two decades, likely reflecting improved diagnostic classification and recognition of other entities within the inflammatory myopathy spectrum, including immune-mediated necrotizing myopathy (IMNM) and inclusion body myositis (IBM). [7]

3. Aetiology & Pathophysiology

Etiology

Polymyositis is an autoimmune disease of unknown etiology. Proposed triggers and contributing factors include:

Environmental Triggers:

• Viral infections (coxsackievirus, influenza, HIV, HTLV-1) may trigger autoimmune responses in genetically susceptible individuals [14]
• UV radiation exposure (less clearly established than in dermatomyositis)
• Certain medications (statins, hydroxyurea, penicillamine) can cause drug-induced myositis mimicking polymyositis [15]
• Vaccinations (rare case reports, causality uncertain)

Genetic Factors:

• HLA class II associations: HLA-DRB103:01, HLA-DQA105:01 [10]
• Non-HLA genes: PTPN22, STAT4, BLK polymorphisms associated with increased risk [16]
• Family clustering rare, but slightly increased risk in first-degree relatives

Autoantibodies and Pathogenesis: The presence of myositis-specific antibodies (MSAs) and myositis-associated antibodies (MAAs) suggests distinct immunopathogenic mechanisms and defines clinical phenotypes.

Molecular and Cellular Pathophysiology

Polymyositis is characterized by CD8+ T-cell-mediated cytotoxic attack on muscle fibers, distinguishing it from dermatomyositis (which involves complement-mediated microangiopathy and CD4+ T cells).

Cellular Mechanisms:

Antigen Presentation on Muscle Fibers (MHC Class I Upregulation)
                    ↓
CD8+ Cytotoxic T-Cell Activation and Clonal Expansion
                    ↓
Direct Cytotoxic Attack on Non-Necrotic Muscle Fibers
                    ↓
Perforin/Granzyme-Mediated Muscle Fiber Destruction
                    ↓
Endomysial Inflammation (inflammation within muscle fascicles)
                    ↓
Muscle Fiber Necrosis + Regeneration Cycles
                    ↓
Progressive Muscle Weakness + Atrophy

Key Pathological Features:

1. Endomysial inflammation: T-cell infiltrates surrounding and invading non-necrotic muscle fibers
2. MHC-I upregulation: Muscle fibers aberrantly express MHC class I molecules, marking them for immune attack
3. Partial muscle fiber invasion: CD8+ T cells directly attack muscle fibers
4. Muscle fiber necrosis and regeneration: Evidence of ongoing damage with variation in fiber size
5. Absence of perifascicular atrophy: Unlike dermatomyositis, atrophy is not predominantly at fascicle peripheries

Autoantibody Profiles and Clinical Phenotypes

Antisynthetase Syndrome: A distinct clinical entity characterized by:

• Inflammatory myopathy (often polymyositis-like)
• Interstitial lung disease (most significant cause of morbidity/mortality)
• Non-erosive inflammatory arthritis
• Raynaud's phenomenon
• Mechanic's hands (hyperkeratotic, cracked skin on palmar/lateral fingers)
• Fever

Anti-Jo-1 is the most common antisynthetase antibody (70-80% of antisynthetase syndrome cases), but other antisynthetase antibodies (PL-7, PL-12, EJ, OJ, KS, Zo, Ha) are recognized. [11]

4. Clinical Presentation

Cardinal Symptoms

Proximal Muscle Weakness (hallmark):

• Insidious onset over weeks to months (subacute progression)
• Symmetric involvement of proximal limb muscles
• Lower limbs typically affected before or more severely than upper limbs
• Difficulty rising from sitting position without using arms
• Difficulty climbing stairs, requiring handrail use
• Difficulty lifting arms above shoulder level (combing hair, reaching high shelves)
• Neck flexor weakness (difficulty lifting head from pillow)
• Trunk muscle involvement less common

Absence of Muscle Pain: Unlike some other myopathies, polymyositis typically causes painless weakness. Mild muscle tenderness may be present in ~25% of cases, but severe myalgia should prompt consideration of alternative diagnoses. [2]

Muscle Fatigue: Progressive weakness with sustained activity, but distinct from the fatigability of myasthenia gravis (which fluctuates within minutes and involves ocular/bulbar muscles early).

Extramuscular Manifestations

Red Flag Features

⚠️ Immediate attention required:

1. Dysphagia: Risk of aspiration pneumonia; may require modified diet or feeding support
2. Respiratory muscle weakness: Progressive dyspnea, orthopnea, or hypercapnic respiratory failure
3. Rapidly progressive weakness: Particularly anti-SRP myopathy; may require ICU-level care
4. Cardiac symptoms: Palpitations, syncope, chest pain suggesting arrhythmia or myocarditis
5. Rhabdomyolysis: Massive CK elevation (> 10,000 U/L) with myoglobinuria and acute kidney injury

5. Clinical Examination

General Inspection

• Body habitus: Muscle wasting may be evident in chronic cases
• Mobility: Observe patient rising from chair (use of arms to push up suggests proximal weakness)
• Gait: Waddling gait or Trendelenburg sign if hip girdle weakness
• Posture: Difficulty holding head upright if neck flexor weakness

Dermatological Examination

Critical to exclude dermatomyositis:

• Heliotrope rash: Violaceous periorbital edema → ABSENT in pure polymyositis
• Gottron's papules: Violaceous papules over MCP/PIP/DIP joints → ABSENT in pure polymyositis
• Gottron's sign: Violaceous erythema over extensor surfaces → ABSENT in pure polymyositis
• V-sign: Erythema over anterior neck/chest → ABSENT in pure polymyositis
• Shawl sign: Erythema over upper back/shoulders → ABSENT in pure polymyositis
• Mechanic's hands: Hyperkeratotic, cracked skin on palmar/lateral fingers → MAY BE PRESENT (antisynthetase syndrome)
• Raynaud's phenomenon: May be present, especially with antisynthetase antibodies

Note: Presence of typical dermatomyositis rashes excludes diagnosis of polymyositis and indicates dermatomyositis.

Motor Examination

Muscle Strength Testing (MRC Scale):

Pattern: Proximal > Distal; Symmetric; Lower limb ≥ Upper limb

Special Tests:

• Gower's sign: Positive (patient uses hands to "climb up" legs when rising from floor)
• Functional tests: Time to rise from chair, time to walk 10 meters, number of stairs climbed

Reflexes and Sensation

• Deep tendon reflexes: Typically preserved (normal) until late disease
• Sensation: Completely normal (distinguishes from neuropathic causes)
• Coordination: Normal

Respiratory Examination

• Respiratory rate and pattern: Tachypnea if ILD or respiratory muscle weakness
• Chest auscultation: Fine bibasal inspiratory crackles if ILD
• Forced vital capacity (FVC): Reduced if respiratory muscle weakness (> 20% reduction significant)
• Oxygen saturation: May be reduced if ILD

Cardiovascular Examination

• Heart rate and rhythm: Check for arrhythmias
• Heart sounds: Muffled if pericardial effusion (rare)
• Signs of heart failure: Elevated JVP, peripheral edema if cardiomyopathy

Other Systems

• Hands: Mechanic's hands (fissured, hyperkeratotic skin on palmar/lateral fingers) in antisynthetase syndrome
• Joints: Inflammatory arthritis (swelling, tenderness) especially MCPs, wrists, knees
• Oropharynx: Assess swallowing; pooling of saliva suggests dysphagia

6. Differential Diagnosis

Proximal muscle weakness has an extensive differential diagnosis. Key considerations include:

1. Other Inflammatory Myopathies

2. Infectious Myositis

• Viral: HIV, HTLV-1, influenza, coxsackievirus (acute onset, systemic features)
• Bacterial: Pyomyositis (focal muscle abscess; fever, focal pain/swelling)
• Parasitic: Trichinosis (eosinophilia, periorbital edema), toxoplasmosis

3. Endocrine and Metabolic Myopathies

4. Drug-Induced Myopathy

• Statins: Most common; CK elevation; myalgia; usually resolves with cessation [15]
• Corticosteroids: Chronic use causes steroid myopathy (normal CK, type 2 fiber atrophy)
• Colchicine: Especially in renal impairment
• Antiretrovirals: Zidovudine (AZT) causes mitochondrial myopathy
• Alcohol: Acute alcoholic rhabdomyolysis or chronic alcoholic myopathy

5. Neuromuscular Junction Disorders

6. Muscular Dystrophies

• Limb-girdle muscular dystrophies (LGMD): Genetic; family history; gradual onset; variable CK elevation
• Becker/Duchenne: X-linked; males; childhood/adolescent onset (Duchenne); dystrophin mutations
• Facioscapulohumeral dystrophy: Facial and scapular involvement; autosomal dominant

7. Motor Neuron and Nerve Disorders

• Amyotrophic lateral sclerosis (ALS): Fasciculations, upper motor neuron signs, normal CK
• Chronic inflammatory demyelinating polyneuropathy (CIDP): Distal > proximal; sensory involvement; elevated CSF protein

8. Malignancy-Associated

• Paraneoplastic myositis: Associated with underlying malignancy; screen all PM patients
• Cancer cachexia: Generalized wasting, advanced malignancy

7. Investigations

Blood Tests

First-Line (Essential)

Interpretation Pearl: Elevated transaminases (AST/ALT) without viral hepatitis or liver disease should prompt CK measurement to exclude myopathy.

Autoantibody Testing (Diagnostic and Prognostic)

Myositis-Specific Antibodies (MSAs):

• Anti-Jo-1 (anti-histidyl-tRNA synthetase): 15-20% of PM; antisynthetase syndrome [11]
• Anti-SRP (signal recognition particle): 5-10%; severe, refractory disease [5]
• Anti-PL-7, PL-12 (threonyl-, alanyl-tRNA synthetases): Antisynthetase syndrome variants
• Anti-Mi-2: Rare in PM; more typical of dermatomyositis
• Anti-HMGCR (HMG-CoA reductase): IMNM, statin-associated; reclassified from PM [7]
• Anti-200/100 (anti-NXP2, anti-TIF1γ): Dermatomyositis; malignancy-associated

Myositis-Associated Antibodies (MAAs):

• Anti-Ro/SSA, anti-La/SSB: 10-15%; ILD risk; overlap with Sjögren's
• Anti-PM/Scl: Polymyositis-scleroderma overlap
• Anti-Ku: Overlap syndromes

General Autoantibodies:

• ANA (antinuclear antibody): Positive in 40-60% (non-specific)
• Rheumatoid factor: May be positive (non-specific)

Other Baseline Tests

• Complete blood count (CBC): Usually normal; lymphopenia possible
• Renal function: Baseline; may be impaired if rhabdomyolysis
• Liver function tests: True hepatic enzymes (alkaline phosphatase, bilirubin, GGT) normal
• Thyroid function (TSH, free T4): Exclude hypothyroid myopathy [19]
• Vitamin D (25-OH vitamin D): Deficiency common; may contribute to weakness
• HbA1c or fasting glucose: Baseline before corticosteroids

Electromyography (EMG)

Typical EMG Findings in Polymyositis:

1. Increased insertional activity: Spontaneous muscle fiber activity
2. Fibrillation potentials and positive sharp waves: Denervation-like activity from muscle fiber necrosis
3. Small, short-duration, polyphasic motor unit potentials: Myopathic pattern
4. Early recruitment: Many motor units fire with minimal effort (weak contraction)
5. Normal nerve conduction studies: Excludes neuropathy

Sensitivity: 70-90% for inflammatory myopathy [21]

Limitations:

• Non-specific; cannot definitively distinguish PM from other myopathies
• Operator-dependent
• Painful; patient tolerance variable

Clinical Use: Helpful to confirm myopathic process and guide biopsy site (biopsy contralateral limb to avoid EMG-induced inflammation artifacts).

Magnetic Resonance Imaging (MRI) of Muscles

Sequences:

• T2-weighted with fat suppression or STIR (short tau inversion recovery): Shows muscle edema (hyperintense signal)
• T1-weighted: Shows muscle atrophy and fatty replacement (chronic disease)

Typical MRI Findings:

• Symmetric proximal muscle edema (high T2/STIR signal)
• Thigh muscles (vastus lateralis, vastus medialis) commonly affected
• Shoulder girdle and paraspinal muscles may be involved

Advantages:

• Non-invasive
• Can identify actively inflamed muscles for biopsy targeting
• Useful for monitoring treatment response
• Distinguishes active inflammation from chronic fatty replacement [22]

Clinical Use: Increasingly used to guide biopsy site selection and assess disease extent without invasive procedures.

Muscle Biopsy (Gold Standard Diagnostic Test)

Indications: Suspected inflammatory myopathy with:

• Elevated CK + proximal weakness
• Uncertain diagnosis despite clinical and laboratory evaluation
• To guide treatment decisions

Biopsy Site Selection:

• Moderately weak muscle (avoid severely atrophied or normal muscles)
• Avoid recent EMG site (wait 2-4 weeks to prevent artifact)
• MRI-guided biopsy preferred (target areas with active inflammation)

Histopathological Features of Polymyositis:

Immunohistochemistry:

• CD8+ T cells predominate (vs. CD4+ in dermatomyositis)
• MHC class I overexpression on muscle fiber sarcolemma
• Absence of complement (C5b-9) deposition (present in dermatomyositis)

Differential Diagnoses on Biopsy:

• Dermatomyositis: Perifascicular atrophy, perivascular inflammation, complement deposition, CD4+ predominance
• Inclusion body myositis: Rimmed vacuoles, endomysial inflammation, amyloid deposits, eosinophilic inclusions
• Immune-mediated necrotizing myopathy: Extensive necrosis, minimal inflammation, macrophages predominate

Pulmonary Function Tests and HRCT Chest

Indications: All patients with polymyositis (ILD present in 30-40%) [11]

Pulmonary Function Tests:

• Reduced FVC (forced vital capacity): Suggests restrictive lung disease (ILD) or respiratory muscle weakness
• Reduced DLCO (diffusing capacity): Sensitive for ILD
• Normal FEV1/FVC ratio: Confirms restrictive pattern

High-Resolution CT (HRCT) Chest:

• Non-specific interstitial pneumonia (NSIP): Most common pattern in antisynthetase syndrome; ground-glass opacities, reticular changes
• Usual interstitial pneumonia (UIP): Less common; honeycombing, traction bronchiectasis; worse prognosis
• Organizing pneumonia (OP): Consolidation, "reversed halo sign"

Follow-Up: Serial PFTs and HRCT to monitor ILD progression or response to treatment.

Cardiac Evaluation

Indications: All patients (cardiac involvement in 10-30%, often subclinical) [13]

Tests:

• ECG: Arrhythmias, conduction defects (PR prolongation, AV block, bundle branch block)
• Echocardiography: Left ventricular function, wall motion abnormalities, pericardial effusion
• Troponin: Elevated if myocarditis or myocardial involvement
• 24-hour Holter monitor: If palpitations or syncope
• Cardiac MRI: Most sensitive for detecting myocardial inflammation; consider if clinical suspicion

Malignancy Screening

Mandatory in all polymyositis patients (malignancy risk 10-25%) [4]

Initial Screening:

• Thorough history and physical examination: Constitutional symptoms, lymphadenopathy, abdominal masses
• Basic investigations:
  • Chest X-ray or CT chest
  • CT abdomen and pelvis
  • Age-appropriate cancer screening (mammography, colonoscopy, PSA)
• Sex-specific:
  • "Women: Pelvic examination, transvaginal ultrasound, CA-125 (ovarian cancer screening)"
  • "Men: PSA, testicular examination"
• Additional: FDG-PET/CT if high suspicion or unexplained constitutional symptoms

Highest Risk Cancers:

• Ovarian (women)
• Lung
• Gastric
• Colorectal
• Pancreatic
• Non-Hodgkin lymphoma

Follow-Up: Repeat cancer screening at 3 years if initial screen negative, as some malignancies manifest later. Continue age-appropriate screening indefinitely.

8. Classification and Diagnostic Criteria

2017 EULAR/ACR Classification Criteria for Idiopathic Inflammatory Myopathies

The most widely used and validated criteria are the 2017 EULAR/ACR criteria, which use a weighted scoring system based on clinical, laboratory, and muscle biopsy features. [23]

Criteria Categories and Scoring:

Interpretation:

• Probable IIM: Score ≥5.5 (without muscle biopsy) or ≥6.7 (with muscle biopsy)
• Definite IIM: Score ≥7.5 (without muscle biopsy) or ≥8.7 (with muscle biopsy)

Polymyositis vs. Dermatomyositis: Absence of skin manifestations (heliotrope rash, Gottron's papules/sign) distinguishes polymyositis from dermatomyositis.

Bohan and Peter Criteria (Historical, 1975)

While largely superseded, the Bohan and Peter criteria are still referenced:

Five Criteria:

1. Symmetric proximal muscle weakness
2. Elevated serum muscle enzymes (CK, aldolase, AST, ALT, LDH)
3. Myopathic changes on EMG
4. Characteristic muscle biopsy findings
5. Typical skin rash (dermatomyositis only)

Diagnosis:

• Definite polymyositis: 4 criteria (excluding criterion 5)
• Probable polymyositis: 3 criteria (excluding criterion 5)

Limitations: Does not account for autoantibodies, MRI findings, or newer diagnostic modalities; less specific than 2017 EULAR/ACR criteria.

9. Management

Management of polymyositis is multifaceted, involving immunosuppression, supportive care, monitoring for complications, and malignancy screening.

General Principles

1. Early diagnosis and treatment: Improves outcomes and prevents irreversible muscle damage
2. Immunosuppression is cornerstone: High-dose corticosteroids + steroid-sparing agents
3. Multidisciplinary approach: Rheumatology, neurology, physiotherapy, respiratory, cardiology as needed
4. Monitoring disease activity: Serial CK, muscle strength assessments, functional measures
5. Screen and manage complications: ILD, cardiac involvement, malignancy
6. Avoid unnecessary muscle damage: Minimize IM injections, excessive EMG, statins

Acute/Initial Management

First-Line: High-Dose Corticosteroids

Regimen:

• Prednisolone 1 mg/kg/day (typically 60-80 mg/day; maximum 100 mg/day) [24]
• Continue high dose for 4-6 weeks until clinical improvement (strength) and CK normalization begins
• Gradual taper over 6-12 months once response achieved (reduce by 10-20% every 2-4 weeks)
• Typical maintenance dose: 5-10 mg/day

IV Methylprednisolone:

• Reserved for severe, rapidly progressive weakness or life-threatening complications
• Dose: 500-1,000 mg IV daily for 3-5 days, then transition to oral prednisolone

Monitoring:

• CK levels weekly initially, then every 2-4 weeks
• Muscle strength assessment (MMT-8, functional measures)
• Adverse effects: Hyperglycemia, hypertension, osteoporosis, infections, psychiatric effects

Steroid-Sparing Agents (Early Initiation Recommended)

To minimize corticosteroid exposure and improve outcomes, initiate steroid-sparing agents early (often at diagnosis or within first few months): [25]

Combination Therapy: Methotrexate + azathioprine has been studied for refractory cases, but evidence is limited.

Management of Refractory Disease

Definition: Inadequate response to high-dose corticosteroids + conventional steroid-sparing agent after 3-6 months, or intolerable steroid side effects.

Biological Agents

Combination Strategies:

• Rituximab + IVIG: For severe refractory disease
• Rituximab + mycophenolate: For ILD-predominant disease

Cyclophosphamide

• Indication: Severe ILD or life-threatening disease unresponsive to other therapies
• Dose: IV pulse (500-1,000 mg/m² monthly for 6 months) or daily oral (1-2 mg/kg/day)
• Toxicity: Bone marrow suppression, infections, hemorrhagic cystitis, infertility, malignancy risk
• Monitoring: CBC, urinalysis, mesna (for hemorrhagic cystitis prophylaxis with IV dosing)

Management of Interstitial Lung Disease (ILD)

First-Line (antisynthetase syndrome or PM-ILD):

• Corticosteroids: Prednisolone 1 mg/kg/day
• Mycophenolate mofetil: 2-3 g/day (preferred for ILD) [29]
• Azathioprine: 2-3 mg/kg/day (alternative)

Refractory ILD:

• Rituximab: Effective for myositis-ILD [30]
• Cyclophosphamide: IV pulse therapy for progressive ILD
• Nintedanib or Pirfenidone: Antifibrotic agents; emerging evidence for autoimmune ILD [31]
• Lung transplantation: For end-stage ILD

Monitoring: Serial PFTs (FVC, DLCO) and HRCT chest every 3-6 months.

Supportive and Adjunctive Therapies

Physiotherapy and Rehabilitation

• Early mobilization: Prevent muscle atrophy and contractures
• Graded exercise program: Aerobic and resistance training (contrary to historical advice to rest)
• Evidence: Supervised exercise is safe and beneficial in stable polymyositis [32]
• Functional goals: Maintain ADLs, prevent falls

Swallowing and Nutrition

• Speech and language therapy (SLT): Swallowing assessment if dysphagia
• Modified diet: Thickened fluids, soft foods to reduce aspiration risk
• Feeding support: Nasogastric tube or PEG if severe dysphagia or malnutrition

Bone Protection (Osteoporosis Prevention)

Patients on long-term corticosteroids require:

• Calcium 1,000-1,200 mg/day + Vitamin D 800-1,000 IU/day
• Bisphosphonate: Alendronate 70 mg weekly or risedronate 35 mg weekly (if DEXA T-score ≤ -1.5 or fragility fracture)
• Baseline DEXA scan and repeat every 1-2 years

Infection Prophylaxis

• Pneumocystis jirovecii pneumonia (PCP) prophylaxis: Co-trimoxazole 480 mg daily or 960 mg thrice weekly if:
  • Prednisolone ≥20 mg/day for > 1 month
  • Multiple immunosuppressants
  • CD4 count less than 200 cells/µL
• Vaccinations:
  • Annual influenza vaccine
  • Pneumococcal vaccine (PCV13 followed by PPSV23)
  • Avoid live vaccines while on immunosuppression
  • COVID-19 vaccination strongly recommended

Other Comorbidity Management

• Cardiovascular risk: Statins if indicated (AVOID if active myositis or elevated CK; consider after disease control)
• Diabetes screening: HbA1c monitoring on corticosteroids
• Hypertension management: Common with corticosteroid use
• Mental health support: Depression and anxiety common; consider screening and referral

Special Populations

Anti-SRP Myopathy

• Severe, often refractory disease [5]
• Requires aggressive immunosuppression: High-dose corticosteroids + early rituximab + IVIG
• Higher risk of cardiac involvement: Cardiac MRI and troponin monitoring
• Prognosis generally poorer; often incomplete recovery

Antisynthetase Syndrome

• ILD is primary determinant of outcome [11]
• Requires dual focus: Myositis treatment + ILD-specific therapy (mycophenolate, rituximab)
• Multidisciplinary management: Rheumatology + respiratory medicine
• Raynaud's phenomenon: Manage with calcium channel blockers (nifedipine, amlodipine)
• Mechanic's hands: Emollients, hand care

Malignancy-Associated Polymyositis

• Treatment of underlying cancer is priority; may lead to myositis resolution
• Immunosuppression as per standard PM protocols
• Close surveillance: Myositis may recur with cancer recurrence [4]

Monitoring and Follow-Up

Regular Monitoring (Every 4-12 Weeks Depending on Disease Activity):

Treatment Targets:

• CK normalization (or return to patient's baseline)
• Improvement in muscle strength (≥20% improvement in MMT-8)
• Functional improvement (ADL independence)
• Minimization of corticosteroid dose (less than 10 mg/day prednisolone)

Relapse Definition:

• Worsening muscle strength (≥20% decrease in MMT-8)
• Rising CK (> 2× baseline or > 500 U/L increase)
• New or worsening extramuscular manifestations (ILD, dysphagia)

Relapse Management:

• Exclude infection, medication non-adherence, alternative diagnoses
• Increase immunosuppression (increase prednisolone, optimize/add steroid-sparing agents)
• Consider rituximab or IVIG for refractory relapses

10. Complications

11. Prognosis & Outcomes

Overall Survival

The prognosis of polymyositis has improved significantly with modern immunosuppressive therapies, particularly early aggressive treatment and use of steroid-sparing agents and biologics.

Mortality Rates:

• 5-year survival: ~80-90% with treatment [33]
• 10-year survival: ~70-80%
• Untreated or delayed treatment: Much poorer outcomes with progressive disability

Causes of Death:

1. Malignancy (30-40% of deaths) [4]
2. Interstitial lung disease (20-30% of deaths) [11]
3. Infection (15-25% of deaths; related to immunosuppression)
4. Cardiac complications (10-15% of deaths) [13]
5. Respiratory failure (from muscle weakness or ILD)

Prognostic Factors

Favorable Prognostic Factors

• Younger age at diagnosis (less than 40 years)
• Early diagnosis and treatment (within 6 months of symptom onset)
• Good response to initial corticosteroid therapy (CK normalization, strength improvement)
• Absence of extramuscular manifestations (especially ILD, cardiac involvement)
• Anti-Mi-2 antibody (though rare in PM; more common in DM; associated with good prognosis)
• Absence of malignancy

Unfavorable Prognostic Factors

• Older age at diagnosis (> 60 years) [34]
• Delayed diagnosis and treatment (> 6 months from symptom onset)
• Severe weakness at presentation (unable to ambulate)
• Presence of dysphagia (aspiration risk, malnutrition)
• Interstitial lung disease (especially UIP pattern on HRCT; progressive ILD) [11]
• Cardiac involvement (myocarditis, arrhythmias, cardiomyopathy) [13]
• Malignancy (prognosis determined by cancer) [4]
• Anti-SRP antibody (severe, refractory disease) [5]
• Anti-PL-7, PL-12 antibodies (associated with severe ILD)
• Poor response to initial treatment (persistent elevation of CK, progressive weakness)

Functional Outcomes

Treatment Response (with corticosteroids + steroid-sparing agents):

• 70-80% achieve disease control: Improvement in muscle strength and CK normalization [24]
• Complete remission (off all treatment): Rare; most require long-term low-dose immunosuppression
• Partial response: Many patients achieve functional independence but have residual weakness or require ongoing therapy
• Refractory disease: 10-20% have inadequate response to conventional therapy; require biologics (rituximab, IVIG) [27,28]

Disability:

• Mild disability: Most patients with good disease control
• Moderate to severe disability: 20-30% have persistent functional impairment (difficulty with stairs, overhead activities)
• Wheelchair dependence: Rare with modern therapy; seen in severe refractory cases or late diagnosis

Quality of Life:

• Fatigue is major persistent symptom even with disease control
• Chronic pain less common than in other rheumatic diseases
• Psychological impact: Depression, anxiety related to chronic disease, steroid side effects, fear of malignancy

Disease Course Patterns

Monocyclic (Single Episode):

• Rare; less than 10% of cases
• Single episode of active disease followed by remission
• May be able to discontinue therapy after several years

Polycyclic (Relapsing-Remitting):

• 30-40% of cases
• Periods of remission alternating with relapses
• Relapses often triggered by tapering corticosteroids too quickly

Chronic Persistent:

• 50-60% of cases
• Continuous disease activity requiring ongoing immunosuppression
• Most common pattern

Long-Term Management and Remission Maintenance

Achieving Remission:

• Target: Clinical remission (normal strength, CK normalization, off corticosteroids or on low-dose maintenance less than 10 mg/day prednisolone)
• Timeline: 6-12 months of therapy to achieve remission; 2-5 years to attempt discontinuation
• Maintenance therapy: Most patients require long-term low-dose steroid-sparing agent (methotrexate, azathioprine, mycophenolate)

Discontinuation of Therapy:

• Attempt only after sustained remission (≥2 years)
• Taper very slowly (reduce by 20-25% every 3-6 months)
• Monitor closely for relapse (CK, strength assessment)
• Many patients require indefinite low-dose therapy

12. Prevention & Screening

Primary Prevention

No established primary prevention strategies exist for polymyositis, as the etiology is unclear and no modifiable risk factors have been definitively identified.

Potential Considerations:

• Avoiding known myotoxic drugs (statins, colchicine) in high-risk individuals (those with other autoimmune diseases or family history)
• UV protection (theoretical; more relevant to dermatomyositis)

Secondary Prevention (Preventing Complications)

Malignancy Screening (see Investigations section):

• Comprehensive age-appropriate cancer screening at diagnosis
• Repeat screening at 3 years if initial negative
• Ongoing surveillance per standard guidelines

Interstitial Lung Disease Monitoring:

• Baseline HRCT chest and PFTs for all patients
• Serial monitoring every 6-12 months, or more frequently if ILD present or antisynthetase antibodies

Cardiac Monitoring:

• Baseline ECG and echocardiography
• Annual ECG; echocardiography if abnormal or symptomatic
• Consider cardiac MRI if high-risk antibodies (anti-SRP) or cardiac symptoms

Osteoporosis Prevention:

• DEXA scan at baseline and periodically
• Calcium, vitamin D, bisphosphonate as indicated

Infection Prevention:

• PCP prophylaxis if immunosuppressed
• Vaccinations (influenza, pneumococcal, COVID-19)
• Patient education on infection risk and early reporting

Tertiary Prevention (Preventing Disability)

Physiotherapy and Exercise:

• Regular supervised exercise programs to maintain muscle strength and function
• Prevent contractures and deconditioning

Falls Prevention:

• Home safety assessment
• Assistive devices (walkers, grab rails) if weakness persists
• Vitamin D repletion

Vocational Support:

• Occupational therapy assessment
• Workplace accommodations if needed

13. Key Guidelines and Evidence

Major Clinical Guidelines

Landmark Clinical Trials and Studies

1. RIM Trial (Rituximab in Myositis) [27]: Randomized trial demonstrating 83% response to rituximab in refractory myositis (primarily dermatomyositis, but also polymyositis); established rituximab as standard for refractory disease.

2. Joffe et al. (1993) [26]: Methotrexate as steroid-sparing agent in myositis; demonstrated efficacy and reduced corticosteroid requirements.

3. Oddis et al. (2005) [28]: IVIG effective for refractory dermatomyositis; also used in polymyositis with benefit.

4. Marie et al. (2018) [29]: Mycophenolate mofetil effective for myositis-associated ILD.

5. Mammen et al. (2011) [7]: Identification of anti-HMGCR antibodies and immune-mediated necrotizing myopathy, leading to reclassification of some "polymyositis" cases.

6. Alexanderson et al. (2007) [32]: Supervised exercise is safe and beneficial in stable myositis, challenging historical recommendations for rest.

14. Exam-Focused Sections

Common Exam Questions (MRCP, FRACP, Rheumatology Exams)

1. "A 45-year-old woman presents with 3 months of progressive difficulty climbing stairs and rising from chairs. What is your differential diagnosis and initial investigations?"

2. "What are the key differences between polymyositis and dermatomyositis on muscle biopsy?"

3. "A patient with polymyositis has anti-Jo-1 antibodies. What is the clinical significance and what additional investigations are required?"

4. "What is the first-line treatment for polymyositis, and what steroid-sparing agents are commonly used?"

5. "What malignancies are associated with polymyositis, and how should patients be screened?"

6. "Describe the pathophysiology of muscle damage in polymyositis. How does this differ from dermatomyositis?"

7. "A patient with polymyositis on prednisolone 60 mg/day for 2 months has no improvement in strength and CK remains elevated. What is your management?"

8. "What are the causes of elevated CK in a patient presenting with proximal muscle weakness?"

Viva Points

Opening Statement: "Polymyositis is a rare, chronic autoimmune inflammatory myopathy characterized by symmetric proximal muscle weakness without cutaneous manifestations, caused by CD8+ T-cell-mediated cytotoxic attack on muscle fibers. It predominantly affects adults aged 40-60 years with a 2:1 female predominance and is associated with significant risks of interstitial lung disease in 30-40% and malignancy in 10-25% of cases, necessitating comprehensive screening."

Key Facts to Mention:

• Epidemiology: Incidence 1-8 per million; prevalence 5-10 per 100,000 [6]
• Pathophysiology: CD8+ T-cell-mediated with endomysial inflammation and MHC-I upregulation [1]
• Presentation: Insidious proximal weakness over weeks-months; CK elevated 10-50× normal [2]
• Diagnostics: Muscle biopsy gold standard (endomysial inflammation, CD8+ T cells); EMG myopathic pattern; MRI shows muscle edema [21,22]
• Antibodies: Anti-Jo-1 (antisynthetase syndrome, ILD), anti-SRP (severe, refractory) [5,11]
• Complications: ILD 30-40%, malignancy 10-25%, dysphagia 30-50% [3,4,17]
• Treatment: High-dose prednisolone 1 mg/kg/day + early steroid-sparing agents (methotrexate, azathioprine); rituximab for refractory disease [24,27]
• Prognosis: 5-year survival ~80-90%; mortality from malignancy, ILD, infection [33]

Diagnostic Approach: "I would confirm the diagnosis using the 2017 EULAR/ACR classification criteria, which incorporate age, muscle weakness pattern, absence of skin manifestations, elevated CK, myopathic EMG, muscle edema on MRI, and characteristic muscle biopsy findings of endomysial inflammation with CD8+ T-cell infiltrates. I would also test for myositis-specific antibodies, particularly anti-Jo-1 and anti-SRP, to guide prognosis and treatment."

Management Approach: "My management would involve high-dose corticosteroids (prednisolone 1 mg/kg/day) as first-line therapy, with early initiation of steroid-sparing agents such as methotrexate or azathioprine to minimize corticosteroid exposure. I would screen for complications including interstitial lung disease with HRCT chest and PFTs, cardiac involvement with ECG and echocardiography, and malignancy with comprehensive age-appropriate cancer screening. For refractory disease, I would consider rituximab, which has Level 1 evidence from the RIM trial showing 83% response rates. Multidisciplinary management with physiotherapy, bone protection, infection prophylaxis, and long-term monitoring is essential."

Common Mistakes (That Fail Candidates)

❌ Mistake 1: Misdiagnosing as dermatomyositis

• Polymyositis has NO skin rash; presence of heliotrope rash or Gottron's papules = dermatomyositis
• Candidates must explicitly state "absence of cutaneous features"

❌ Mistake 2: Missing malignancy screening

• 10-25% association with cancer; mandatory comprehensive screening at diagnosis
• Failure to mention cancer screening is a critical omission

❌ Mistake 3: Inadequate investigation of ILD

• ILD present in 30-40%, especially with anti-Jo-1; HRCT chest and PFTs are mandatory
• Candidates must mention ILD screening in initial workup

❌ Mistake 4: Wrong first-line treatment

• High-dose corticosteroids (prednisolone 1 mg/kg/day) are first-line
• Starting with low-dose steroids or biologics first = wrong

❌ Mistake 5: Not initiating steroid-sparing agents early

• Modern practice: start methotrexate or azathioprine early (within first few months)
• Waiting for steroid failure before adding steroid-sparing agents is outdated

❌ Mistake 6: Confusing EMG/biopsy findings

• EMG: Myopathic pattern (small, short, polyphasic potentials; early recruitment)
• Biopsy: Endomysial inflammation with CD8+ T cells (NOT perifascicular atrophy)
• Perifascicular atrophy = dermatomyositis, not polymyositis

❌ Mistake 7: Missing anti-Jo-1/antisynthetase syndrome

• Anti-Jo-1 = antisynthetase syndrome (myositis + ILD + arthritis + mechanic's hands + Raynaud's)
• Failure to recognize this distinct phenotype and screen for ILD

❌ Mistake 8: Attributing elevated AST/ALT to liver disease

• Elevated transaminases in myositis are from muscle, not liver
• Must check CK to differentiate; true hepatic enzymes (ALP, bilirubin, GGT) are normal

Model Answers

Q: Describe your approach to investigating a patient with suspected polymyositis.

A: "I would approach this systematically. First, I would take a detailed history focusing on the pattern and time course of weakness, presence of muscle pain, systemic features, medication history (particularly statins), and family history. Examination would assess muscle strength using the MRC scale with particular attention to proximal muscle groups, and I would specifically examine the skin to exclude dermatomyositis rashes.

Initial investigations would include serum creatine kinase, which is typically markedly elevated (10-50 times normal), along with aldolase, LDH, and transaminases. I would check thyroid function to exclude hypothyroid myopathy and vitamin D levels. Autoantibody testing would include ANA, myositis-specific antibodies (anti-Jo-1, anti-SRP, anti-Mi-2, anti-PL-7, anti-PL-12) to guide prognosis and identify clinical phenotypes such as antisynthetase syndrome.

For tissue diagnosis, I would perform electromyography to confirm a myopathic pattern (small, short-duration, polyphasic potentials with early recruitment), and MRI of thigh muscles to identify areas of active inflammation to guide biopsy site selection. Muscle biopsy is the gold standard and would show endomysial inflammation with CD8+ T-cell infiltrates surrounding and invading non-necrotic muscle fibers, with MHC class I upregulation.

Given the association with interstitial lung disease (30-40%), I would perform high-resolution CT chest and pulmonary function tests at baseline. Cardiac involvement occurs in 10-30%, so ECG and echocardiography would be performed. Most importantly, given the 10-25% association with malignancy, I would perform comprehensive age-appropriate cancer screening including CT chest-abdomen-pelvis, and sex-specific screening such as mammography and pelvic imaging in women."

Q: How would you manage a patient with newly diagnosed polymyositis?

A: "Management of polymyositis is multifaceted, involving immunosuppression, complication screening, and supportive care.

For immunosuppression, I would initiate high-dose corticosteroids as first-line therapy—specifically prednisolone 1 mg/kg/day (typically 60-80 mg daily) for 4-6 weeks until clinical improvement and CK normalization begin, followed by a gradual taper over 6-12 months. To minimize corticosteroid exposure and improve long-term outcomes, I would initiate a steroid-sparing agent early, with methotrexate 15-25 mg weekly as my preferred first-line agent, along with folic acid supplementation. Azathioprine 2-3 mg/kg/day or mycophenolate mofetil 2-3 g/day are alternatives, particularly mycophenolate if interstitial lung disease is present.

I would provide bone protection with calcium, vitamin D, and a bisphosphonate if indicated based on DEXA scanning. Given the significant immunosuppression, I would prescribe Pneumocystis prophylaxis with co-trimoxazole and ensure the patient receives influenza and pneumococcal vaccinations.

Multidisciplinary involvement is essential: physiotherapy for graded exercise programs to maintain muscle function, speech and language therapy if dysphagia is present, and respiratory follow-up if ILD is identified. I would monitor disease activity with serial CK measurements and muscle strength assessments (MMT-8) every 2-4 weeks initially, then every 3 months once stable.

If the disease proves refractory to conventional therapy after 3-6 months, I would escalate to rituximab, which has Level 1 evidence from the RIM trial demonstrating 83% response rates in refractory myositis, or consider intravenous immunoglobulin for severe cases. Long-term management requires ongoing surveillance for malignancy, monitoring for ILD progression, and management of treatment-related complications."

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15. References

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2. Lundberg IE, de Visser M, Werth VP. Classification of myositis. Nat Rev Rheumatol. 2018;14(5):269-278. doi:10.1038/nrrheum.2018.41

3. Fathi M, Lundberg IE. Interstitial lung disease in polymyositis and dermatomyositis. Curr Opin Rheumatol. 2005;17(6):701-706. doi:10.1097/01.bor.0000179949.07537.18

4. Hill CL, Zhang Y, Sigurgeirsson B, et al. Frequency of specific cancer types in dermatomyositis and polymyositis: a population-based study. Lancet. 2001;357(9250):96-100. doi:10.1016/S0140-6736(00)03540-6

5. Targoff IN, Johnson AE, Miller FW. Antibody to signal recognition particle in polymyositis. Arthritis Rheum. 1990;33(9):1361-1370. doi:10.1002/art.1780330908

6. Lilleker JB, Vencovsky J, Wang G, et al. The EuroMyositis registry: an international collaborative tool to facilitate myositis research. Ann Rheum Dis. 2018;77(1):30-39. doi:10.1136/annrheumdis-2017-211868

7. Mammen AL, Chung T, Christopher-Stine L, et al. Autoantibodies against 3-hydroxy-3-methylglutaryl-coenzyme A reductase in patients with statin-associated autoimmune myopathy. Arthritis Rheum. 2011;63(3):713-721. doi:10.1002/art.30156

8. Rider LG, Nistala K. The juvenile idiopathic inflammatory myopathies: pathogenesis, clinical and autoantibody phenotypes, and outcomes. J Intern Med. 2016;280(1):24-38. doi:10.1111/joim.12444

9. Bendewald MJ, Wetter DA, Li X, Davis MD. Incidence of dermatomyositis and clinically amyopathic dermatomyositis: a population-based study in Olmsted County, Minnesota. Arch Dermatol. 2010;146(1):26-30. doi:10.1001/archdermatol.2009.328

10. Chinoy H, Plumb L, Lamb JA, et al. HLA-DPB1 associations differ between DRB1*03 positive anti-Jo-1 and anti-PM-Scl antibody positive idiopathic inflammatory myopathy. Rheumatology (Oxford). 2019;58(7):1173-1179. doi:10.1093/rheumatology/key421

11. Connors GR, Christopher-Stine L, Oddis CV, Danoff SK. Interstitial lung disease associated with the idiopathic inflammatory myopathies: what progress has been made in the past 35 years? Chest. 2010;138(6):1464-1474. doi:10.1378/chest.10-0180

12. Tani C, Carli L, Vagnani S, et al. The diagnosis and classification of mixed connective tissue disease. J Autoimmun. 2014;48-49:46-49. doi:10.1016/j.jaut.2014.01.008

13. Lundberg IE, Tjärnlund A, Bottai M, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. Ann Rheum Dis. 2017;76(12):1955-1964. doi:10.1136/annrheumdis-2017-211468

14. Katz U, Shoenfeld Y, Zandman-Goddard G. Update on intravenous immunoglobulins (IVIg) mechanisms of action and off-label use in autoimmune diseases. Curr Pharm Des. 2011;17(29):3166-3175. doi:10.2174/138161211798157540

15. Alves M, Almeida R, Almeid H. Statin-induced myopathy: a review of genetic susceptibility. Curr Genomics. 2019;20(8):574-582. doi:10.2174/1389202921666191223155925

16. Miller FW, Chen W, O'Hanlon TP, et al. Genome-wide association study identifies HLA 8.1 ancestral haplotype alleles as major genetic risk factors for myositis phenotypes. Genes Immun. 2015;16(7):470-480. doi:10.1038/gene.2015.28

17. Ertekin C, Yüceyar N, Aydoğdu I. Clinical and electrophysiological evaluation of dysphagia in myasthenia gravis. J Neurol Neurosurg Psychiatry. 1998;65(6):848-856. doi:10.1136/jnnp.65.6.848

18. Greenberg SA. Inclusion body myositis: clinical features and pathogenesis. Nat Rev Rheumatol. 2019;15(5):257-272. doi:10.1038/s41584-019-0186-x

19. Riggs JE. Neurologic manifestations of endocrine disease. Neurol Clin. 2002;20(1):35-58. doi:10.1016/s0733-8619(03)00060-0

20. Gilhus NE, Verschuuren JJ. Myasthenia gravis: subgroup classification and therapeutic strategies. Lancet Neurol. 2015;14(10):1023-1036. doi:10.1016/S1474-4422(15)00145-3

21. Olsen NJ, Qi C, Wluka AE. The utility of electromyography in the diagnosis of inflammatory myopathies. Curr Rheumatol Rep. 2010;12(1):69-74. doi:10.1007/s11926-009-0080-x

22. Tomasová Studynková J, Charvát F, Jarosová K, Vencovsky J. The role of MRI in the assessment of polymyositis and dermatomyositis. Rheumatology (Oxford). 2007;46(7):1174-1179. doi:10.1093/rheumatology/kem088

23. Lundberg IE, Tjärnlund A, Bottai M, et al. 2017 European League Against Rheumatism/American College of Rheumatology classification criteria for adult and juvenile idiopathic inflammatory myopathies and their major subgroups. Arthritis Rheumatol. 2017;69(12):2271-2282. doi:10.1002/art.40320

24. Joffe MM, Love LA, Leff RL, et al. Drug therapy of the idiopathic inflammatory myopathies: predictors of response to prednisone, azathioprine, and methotrexate and a comparison of their efficacy. Am J Med. 1993;94(4):379-387. doi:10.1016/0002-9343(93)90148-i

25. Gordon PA, Winer JB, Hoogendijk JE, Choy EH. Immunosuppressant and immunomodulatory treatment for dermatomyositis and polymyositis. Cochrane Database Syst Rev. 2012;8:CD003643. doi:10.1002/14651858.CD003643.pub4

26. Joffe MM, Love LA, Leff RL, et al. Drug therapy of the idiopathic inflammatory myopathies: predictors of response to prednisone, azathioprine, and methotrexate and a comparison of their efficacy. Am J Med. 1993;94(4):379-387. doi:10.1016/0002-9343(93)90148-i

27. Oddis CV, Reed AM, Aggarwal R, et al. Rituximab in the treatment of refractory adult and juvenile dermatomyositis and adult polymyositis: a randomized, placebo-phase trial. Arthritis Rheum. 2013;65(2):314-324. doi:10.1002/art.37754

28. Dalakas MC, Illa I, Dambrosia JM, et al. A controlled trial of high-dose intravenous immune globulin infusions as treatment for dermatomyositis. N Engl J Med. 1993;329(27):1993-2000. doi:10.1056/NEJM199312303292704

29. Marie I, Hachulla E, Chérin P, et al. Interstitial lung disease in polymyositis and dermatomyositis. Arthritis Rheum. 2002;47(6):614-622. doi:10.1002/art.10794

30. Allenbach Y, Guiguet M, Rigolet A, et al. Efficacy of rituximab in refractory inflammatory myopathies associated with anti-synthetase auto-antibodies: an open-label, phase II trial. PLoS One. 2015;10(11):e0133702. doi:10.1371/journal.pone.0133702

31. Distler O, Highland KB, Gahlemann M, et al. Nintedanib for systemic sclerosis–associated interstitial lung disease. N Engl J Med. 2019;380(26):2518-2528. doi:10.1056/NEJMoa1903076

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34. Dobloug GC, Garen T, Brunborg C, et al. Survival and cancer risk in an unselected and complete Norwegian idiopathic inflammatory myopathy cohort. Semin Arthritis Rheum. 2015;45(3):301-308. doi:10.1016/j.semarthrit.2015.06.005

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16. Patient / Layperson Explanation

What is polymyositis?

Polymyositis is a rare condition where your immune system mistakenly attacks your own muscles, causing them to become weak and inflamed. This is called an "autoimmune" disease. The muscles closest to the center of your body—like your shoulders, hips, thighs, and neck—are most affected. Unlike a similar condition called dermatomyositis, polymyositis does not cause a skin rash.

What causes it?

We don't fully understand what causes polymyositis. It's thought that a combination of genetic factors (genes you inherit) and environmental triggers (like infections) can cause your immune system to mistakenly attack your muscles. It is not contagious, and you cannot catch it from someone else.

What are the symptoms?

The main symptom is muscle weakness that gets worse over weeks to months. You might notice:

• Difficulty getting up from a chair or out of bed
• Trouble climbing stairs or walking uphill
• Struggling to lift your arms above your head (like combing your hair or reaching for something on a high shelf)
• Difficulty lifting your head off a pillow
• Sometimes difficulty swallowing or shortness of breath

The weakness is usually the same on both sides of your body and is typically painless or only mildly uncomfortable.

How is it diagnosed?

Your doctor will:

• Ask about your symptoms and examine your muscle strength
• Take blood tests to check for muscle damage (a protein called creatine kinase, or CK, is usually very high)
• Perform tests like an EMG (electrical test of muscles) or MRI scan to look at your muscles
• Sometimes take a small sample of muscle (muscle biopsy) to look at under a microscope

Are there complications?

Yes, polymyositis can affect other parts of your body:

• Lungs: About 30-40% of people develop lung scarring (interstitial lung disease), which can cause shortness of breath
• Swallowing: Difficulty swallowing can lead to choking or aspiration (food going into your lungs)
• Heart: Rarely, the heart muscle or heart rhythm can be affected
• Cancer: There is a small increased risk of cancer (10-25%), so your doctor will screen you for this

How is it treated?

Treatment aims to reduce inflammation and help your muscles recover:

1. Steroid medications (like prednisolone): The main treatment to reduce inflammation. You'll start with a high dose and gradually reduce it over many months.

2. Other immune-suppressing drugs: Medicines like methotrexate, azathioprine, or mycophenolate are often added to reduce the amount of steroids you need and control the disease long-term.

3. Physiotherapy: Exercises to help maintain and rebuild your muscle strength.

4. Monitoring: Regular blood tests, lung function tests, and checks for cancer.

5. Advanced treatments: If the standard treatments don't work well, stronger medicines like rituximab (a biological therapy) or intravenous immunoglobulin (IVIG) may be used.

What's the outlook?

With treatment, most people (70-80%) improve significantly. However, polymyositis is usually a long-term (chronic) condition that requires ongoing treatment and monitoring. Some people can reduce or stop their medicines after several years, but many need to stay on low doses indefinitely. The main factors affecting long-term health are lung disease, cancer, and side effects from medications.

What can I do to help myself?

• Take your medications as prescribed, even when you feel better
• Stay as active as you can—gentle exercise is safe and beneficial
• Attend all follow-up appointments and tests
• Report any new symptoms (especially breathing problems, swallowing difficulties, or unexplained weight loss) to your doctor promptly
• Protect your bones (take calcium and vitamin D) if you're on long-term steroids
• Avoid infections by washing hands regularly and getting recommended vaccinations
• Join a support group to connect with others living with polymyositis

Remember, every person's experience with polymyositis is different. Work closely with your medical team to develop a treatment plan that's right for you.