Hashimoto's Thyroiditis

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1. Overview

Hashimoto's Thyroiditis (Chronic Lymphocytic Thyroiditis) is the most common cause of hypothyroidism in iodine-sufficient regions, affecting 1-2% of the general population. [1,2] It is an organ-specific autoimmune disease characterised by lymphocytic infiltration of the thyroid gland, progressive follicular destruction, and the presence of circulating anti-thyroid antibodies—particularly Anti-Thyroid Peroxidase (Anti-TPO) antibodies.

The condition was first described by Japanese surgeon Hakaru Hashimoto in 1912, who identified the characteristic histological pattern of lymphocytic infiltration and follicular destruction. The disease typically presents insidiously over months to years, progressing from euthyroid autoimmunity through subclinical hypothyroidism to overt thyroid failure. [3]

Clinical Importance

Hashimoto's thyroiditis represents a major public health burden:

• Prevalence: Anti-TPO antibodies are detectable in approximately 10-15% of adult women and 2-5% of adult men, though not all develop clinical hypothyroidism. [4]
• Progression: Approximately 2-5% of individuals with positive anti-TPO antibodies progress to overt hypothyroidism annually. [5]
• Complications: Untreated hypothyroidism increases cardiovascular risk, impairs cognitive function, and in pregnancy, adversely affects fetal neurodevelopment. [6,7]
• Malignancy: Hashimoto's thyroiditis confers a 40-80 fold increased risk of primary thyroid lymphoma compared to the general population. [8]

Key Clinical Features

• Hypothyroidism: Fatigue, weight gain, cold intolerance, constipation, cognitive slowing
• Goitre: Often firm, rubbery, and non-tender initially; may become atrophic in late disease
• Antibodies: Anti-TPO antibodies present in > 90% of cases; Anti-Thyroglobulin (Anti-Tg) in 50-70%
• Autoimmune associations: Increased prevalence of other autoimmune conditions (Type 1 diabetes, Coeliac disease, Addison's disease, Vitiligo)

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2. Epidemiology

Prevalence and Incidence

Hashimoto's thyroiditis demonstrates striking demographic patterns:

Risk Factors

Genetic Factors

• Twin concordance: 30-60% in monozygotic twins vs 3-9% in dizygotic twins [10]
• HLA associations: HLA-DR3, HLA-DR4, HLA-DR5 in Caucasian populations [11]
• CTLA-4 polymorphisms: Associated with susceptibility to multiple autoimmune conditions [11]
• PTPN22 gene: Risk variant (620W allele) increases susceptibility [12]
• Thyroglobulin gene polymorphisms: Associated with disease risk [12]

Environmental Factors

• Iodine intake: Both excess and deficiency can trigger autoimmunity; optimal intake is protective [13]
• Selenium deficiency: May exacerbate autoimmune thyroid disease [13]
• Smoking: Paradoxically protective (unlike Graves' disease where it is a risk factor) [14]
• Pregnancy: Postpartum thyroiditis affects 5-10% of women; 20-40% develop permanent hypothyroidism [15]
• Viral infections: Potential triggers (hepatitis C, Coxsackie virus) [16]
• Medications: Interferon-α, checkpoint inhibitors (anti-PD-1/PD-L1), amiodarone, lithium [17]

Associated Conditions (Polyautoimmunity)

Patients with Hashimoto's have increased risk of:

• Type 1 Diabetes: 3-4 fold increased prevalence [18]
• Coeliac Disease: 2-5% prevalence (10-fold higher than general population) [19]
• Addison's Disease: Part of Autoimmune Polyglandular Syndrome (APS) Type 2 (Schmidt's Syndrome) [20]
• Pernicious Anaemia: 10-15% prevalence [18]
• Vitiligo: 4-8% prevalence [18]
• Rheumatoid Arthritis: 2-3 fold increased prevalence [18]
• Sjögren's Syndrome: Common overlap [18]

Geographic and Ethnic Variation

• Higher prevalence in populations with adequate iodine intake
• Lower prevalence in Asian populations compared to Caucasians (genetic factors)
• Increasing incidence globally, partly due to improved detection

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3. Aetiology and Pathophysiology

Aetiology

Hashimoto's thyroiditis is a multifactorial autoimmune disease resulting from interaction between genetic predisposition and environmental triggers leading to loss of immune tolerance to thyroid antigens.

Primary Autoimmune Mechanism

The fundamental defect is loss of T-cell tolerance to thyroid autoantigens, primarily:

• Thyroid Peroxidase (TPO): Enzyme crucial for thyroid hormone synthesis
• Thyroglobulin (Tg): Precursor protein for T3 and T4
• TSH Receptor (less commonly than in Graves' disease)

Pathophysiology

Molecular and Cellular Mechanisms

Exam Detail: Stage 1: Loss of Immune Tolerance

• Failure of central tolerance (thymic deletion of autoreactive T cells)
• Breakdown of peripheral tolerance mechanisms (regulatory T-cell dysfunction)
• Aberrant expression of HLA Class II molecules on thyroid follicular cells (induced by IFN-γ)
• Molecular mimicry following viral infection may trigger cross-reactive immune responses

Stage 2: Immune Cell Infiltration

• CD4+ T helper cells (Th1 predominant) infiltrate the thyroid gland
• Th1 cells secrete IFN-γ, IL-2, and TNF-α, promoting cell-mediated immunity
• B lymphocytes infiltrate and form germinal centres within the thyroid
• Plasma cells produce anti-thyroid antibodies (Anti-TPO, Anti-Tg)

Stage 3: Thyrocyte Destruction Multiple mechanisms contribute to follicular cell death:

1. Antibody-Dependent Cell-Mediated Cytotoxicity (ADCC):

   • Anti-TPO antibodies bind to thyroid follicular cells
   • NK cells recognise Fc portion and induce apoptosis

2. Complement-Mediated Cytotoxicity:

   • Antibody-antigen complexes activate classical complement pathway
   • Membrane attack complex (MAC) formation causes cell lysis

3. CD8+ Cytotoxic T-Lymphocytes:

   • Direct killing of thyroid follicular cells via perforin/granzyme pathway
   • Fas-FasL mediated apoptosis

4. Cytokine-Mediated Damage:

   • TNF-α and IFN-γ induce apoptosis and inhibit thyrocyte function

Stage 4: Fibrosis and Atrophy

• Progressive replacement of functional thyroid tissue with fibrous tissue
• Loss of follicular architecture
• Eventual gland atrophy in late-stage disease (atrophic variant)

Histopathological Features

Classic microscopic findings include:

1. Diffuse lymphocytic infiltration: T cells, B cells, plasma cells, and macrophages
2. Germinal centre formation: Organised lymphoid follicles within thyroid tissue
3. Hürthle cells (Ashkenazy cells): Eosinophilic metaplastic follicular cells with abundant mitochondria (oxyphilic cells)
4. Follicular atrophy: Loss of colloid, collapsed follicles
5. Fibrosis: Progressive collagen deposition
6. Squamous metaplasia: May be present in severe cases

Antibody Profiles

Natural History and Disease Progression

Phase 1: Euthyroid Hashimoto's (Antibody-positive, normal thyroid function)

• Anti-TPO antibodies present
• Normal TSH and Free T4
• May have subtle ultrasound changes
• 2-5% annual progression to subclinical hypothyroidism [5]

Phase 2: Subclinical Hypothyroidism

• Elevated TSH (> 4.5 mU/L, typically 4.5-10 mU/L)
• Normal Free T4
• Minimal or absent symptoms
• 2-6% annual progression to overt hypothyroidism [5]

Phase 3: Overt Hypothyroidism

• Elevated TSH (> 10 mU/L)
• Low Free T4
• Symptomatic hypothyroidism
• Requires levothyroxine replacement

Special Variant: Hashitoxicosis

• Transient hyperthyroid phase early in disease course (5-10% of cases)
• Results from inflammatory destruction releasing pre-formed thyroid hormone
• Self-limiting over 2-8 weeks
• Eventually progresses to hypothyroidism
• Differentiate from Graves' disease by absent TSH receptor stimulating antibodies and low radioiodine uptake

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4. Clinical Presentation

The clinical presentation of Hashimoto's thyroiditis is highly variable, ranging from asymptomatic biochemical abnormalities to severe, life-threatening myxoedema coma. Most patients present insidiously over months to years.

Symptoms

Metabolic and Constitutional

• Fatigue and lethargy: Most common presenting symptom (80-90%)
• Weight gain: Modest (2-5 kg), due to fluid retention and decreased metabolic rate
• Cold intolerance: Preferring warmer environments, wearing extra layers
• Decreased appetite: Paradoxical weight gain despite reduced food intake

Neuropsychiatric

• Cognitive slowing: "Brain fog", poor concentration, memory impairment
• Depression: May be the primary presenting feature
• Psychomotor retardation: Slow speech, slow movements
• Carpal tunnel syndrome: Due to myxoedematous infiltration of flexor retinaculum (10-15% of cases)
• Cerebellar ataxia: Rare but recognised complication

Dermatological

• Dry, coarse skin: Loss of moisture and elasticity
• Hair changes: Thinning scalp hair, loss of outer third of eyebrows ("Queen Anne's sign"—controversial specificity)
• Brittle nails
• Myxoedema: Non-pitting oedema affecting face (periorbital puffiness), hands, and pre-tibial areas
• Vitiligo: Co-existent autoimmune condition (4-8%)

Gastrointestinal

• Constipation: Due to decreased gut motility (50-60%)
• Mild weight gain: Despite normal or decreased appetite

Cardiovascular

• Bradycardia: Heart rate less than 60 bpm
• Diastolic hypertension: Due to increased systemic vascular resistance
• Pericardial effusion: Usually asymptomatic; rarely causes tamponade (5-10% of severe cases)
• Increased atherosclerotic risk: Due to dyslipidaemia and endothelial dysfunction

Reproductive

• Menorrhagia: Heavy menstrual bleeding (30-40% of premenopausal women)
• Oligomenorrhoea or amenorrhoea: In severe cases
• Infertility: Anovulation due to hyperprolactinaemia and hypothalamic dysfunction
• Recurrent miscarriage: Increased risk in subclinical and overt hypothyroidism (2-4 fold)

Musculoskeletal

• Myalgia: Muscle aches and stiffness (30-40%)
• Proximal myopathy: Weakness affecting shoulder and hip girdle muscles
• Arthralgia: Joint pains
• Delayed relaxation of deep tendon reflexes: "Hung-up" reflexes, most evident at ankle jerks (Woltman's sign)

Signs on Examination

General Inspection

• Slow movements and speech (bradykinesia)
• Facial puffiness (periorbital oedema)
• Expressionless facies
• Inappropriate clothing for ambient temperature (wearing jumpers in warm weather)
• Pale, dry, cool skin
• Thinning scalp hair, loss of lateral eyebrows

Vital Signs

• Bradycardia: Heart rate 50-60 bpm
• Diastolic hypertension: BP 140-160/90-100 mmHg
• Hypothermia: Core temperature may be 1-2°C below normal in severe cases

Thyroid Examination

Inspection:

• Visible goitre (50-60% of cases; absent in atrophic variant)
• Symmetrical enlargement typically
• No overlying skin changes (unlike De Quervain's thyroiditis)

Palpation:

• Texture: Firm, rubbery, "pebbly" or "bosselated" surface
• Size: Typically 2-4 times normal (40-80g vs normal 15-25g)
• Tenderness: Usually non-tender (tenderness suggests subacute thyroiditis)
• Nodularity: Diffuse micronodularity ("pseudonodules" due to irregular fibrosis)
• Mobility: Moves with swallowing
• Lymphadenopathy: Check cervical nodes (lymphoma risk)

Percussion: Retrosternal dullness if retrosternal extension

Auscultation: Bruits absent (unlike Graves' disease with thyroid bruit)

Cardiovascular

• Bradycardia
• Muffled heart sounds (if pericardial effusion)
• Non-pitting oedema of lower limbs

Neurological

• Reflexes: Delayed relaxation phase of ankle jerks (pathognomonic sign)
• Proximal myopathy: Difficulty rising from chair or climbing stairs
• Carpal tunnel syndrome: Positive Tinel's and Phalen's tests
• Cerebellar signs: Rare—ataxia, dysmetria

Other Systems

• Dry, coarse skin
• Brittle hair and nails
• Vitiligo (autoimmune association)

Atypical Presentations

• Hashitoxicosis: Transient thyrotoxic phase (tremor, palpitations, anxiety) followed by hypothyroidism
• Euthyroid Hashimoto's: Goitre with positive antibodies but normal thyroid function
• Atrophic variant: No goitre; gland is fibrosed and shrunken
• Painless (silent) thyroiditis: Postpartum thyroiditis variant

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5. Differential Diagnosis

The differential diagnosis of hypothyroidism with or without goitre includes:

Primary Hypothyroidism

Thyroiditis Variants

Secondary and Tertiary Hypothyroidism

Conditions Mimicking Hypothyroidism

• Chronic fatigue syndrome: Normal thyroid function tests
• Depression: Overlap in symptoms; check TSH
• Anaemia: Fatigue and cold intolerance; check FBC
• Nephrotic syndrome: Oedema and hypoalbuminaemia; check urinalysis
• Obstructive sleep apnoea: Fatigue and cognitive slowing

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6. Investigations

First-Line Investigations

Thyroid Function Tests

Serum TSH (Thyroid Stimulating Hormone):

• Most sensitive screening test for primary hypothyroidism
• Normal range: 0.4-4.0 mU/L (varies by laboratory)
• Subclinical hypothyroidism: TSH 4.5-10 mU/L with normal Free T4
• Overt hypothyroidism: TSH > 10 mU/L with low Free T4
• Sensitivity: > 99% for detecting primary thyroid dysfunction [21]

Free T4 (Free Thyroxine):

• Normal range: 10-20 pmol/L (varies by laboratory)
• Low in overt hypothyroidism
• Normal in subclinical hypothyroidism
• Free T4 is preferred over Total T4 (not affected by binding protein alterations)

Free T3:

• Generally NOT required for diagnosis
• May be normal even when Free T4 is low (peripheral conversion compensates)
• Useful if T3 toxicosis or non-thyroidal illness suspected

Autoantibody Testing

Anti-Thyroid Peroxidase (Anti-TPO) Antibodies:

• Positive in > 90% of Hashimoto's patients [1]
• Titre > 100 IU/mL considered strongly positive
• High titres correlate with disease severity and progression risk
• Sensitivity: 90-95%, Specificity: 90% for autoimmune hypothyroidism [22]

Anti-Thyroglobulin (Anti-Tg) Antibodies:

• Positive in 50-70% of Hashimoto's patients
• Less sensitive than Anti-TPO
• Occasionally the sole positive marker (5-10% of cases)
• Can interfere with serum thyroglobulin measurement

TSH Receptor Antibodies (TRAb):

• Usually negative in Hashimoto's
• TSH receptor blocking antibodies may be present in atrophic variant (10-15%)
• TSH receptor stimulating antibodies suggest Graves' disease (alternative diagnosis)

Exam Detail: When to Order Antibody Tests:

1. Confirm autoimmune aetiology in newly diagnosed hypothyroidism
2. Euthyroid patient with goitre
3. Subclinical hypothyroidism (helps predict progression)
4. Pregnancy planning in women with TSH > 2.5 mU/L (Anti-TPO positive women need closer monitoring)
5. Unexplained infertility or recurrent miscarriage

Interpretation Pitfalls:

• False negatives: 5-10% of Hashimoto's patients may be antibody-negative (seronegative variant)
• False positives: Low-titre Anti-TPO antibodies (10-50 IU/mL) can occur in 10-15% of healthy individuals, especially elderly women
• Antibody titres do NOT correlate with disease activity once diagnosis is established; no need for serial monitoring

Supportive Investigations

Lipid Profile

• Hypercholesterolaemia: Elevated total cholesterol and LDL-cholesterol (50-60% of hypothyroid patients)
• Mechanism: Decreased LDL receptor expression and reduced cholesterol catabolism
• Often improves or resolves with levothyroxine treatment

Creatine Kinase (CK)

• Elevated in 30-50% of hypothyroid patients (typically 2-10 times upper limit of normal)
• Reflects muscle involvement (hypothyroid myopathy)
• Important: Can mimic rhabdomyolysis or statin-induced myopathy

Full Blood Count (FBC)

• Normocytic normochromic anaemia: Most common (mild, Hb 100-120 g/L)
• Macrocytic anaemia: If co-existent pernicious anaemia or B12 deficiency (autoimmune association)
• Mechanism: Decreased erythropoietin, reduced bone marrow activity

Electrolytes

• Hyponatraemia: Due to impaired free water clearance (SIADH-like picture) in severe hypothyroidism

Second-Line/Specialist Investigations

Thyroid Ultrasound

Indications:

1. Palpable thyroid nodule or asymmetric enlargement
2. Suspected malignancy (rapid growth, hard texture, lymphadenopathy)
3. Assessment of goitre size
4. Guided fine-needle aspiration (FNA) if nodule present

Typical Findings in Hashimoto's:

• Heterogeneous echotexture: "Moth-eaten" or "Swiss cheese" appearance
• Hypoechoic gland: Compared to surrounding neck muscles
• Pseudonodules: Multiple small hypoechoic areas (fibrosis, not true nodules)
• Increased vascularity: On Doppler imaging (inflammation)
• Diffuse enlargement: In goitrous variant
• Atrophy: In late-stage disease

Exam Detail: Ultrasound Features Suggesting Malignancy (requires FNA):

• Dominant solid nodule with microcalcifications
• Hypoechoic solid nodule with irregular margins
• Taller-than-wide shape
• Increased central vascularity
• Suspicious cervical lymphadenopathy (loss of fatty hilum, increased vascularity, microcalcifications)

Note: Hashimoto's patients have 2-3 fold increased risk of papillary thyroid carcinoma [8]; maintain vigilance for nodules.

Fine-Needle Aspiration Cytology (FNAC)

Indications:

• Dominant nodule > 1 cm (especially with suspicious ultrasound features)
• Rapidly enlarging goitre (consider lymphoma)
• Hard, fixed mass
• Hoarseness (possible recurrent laryngeal nerve involvement)

Cytology Findings in Hashimoto's:

• Lymphocytes, plasma cells, Hürthle cells
• Sparse colloid
• Follicular cells with Hürthle cell metaplasia

Radioiodine Uptake Scan (RAI Scan)

Rarely indicated in Hashimoto's diagnosis; main uses:

• Differentiating Hashitoxicosis from Graves' disease (low uptake in Hashitoxicosis, high in Graves')
• Evaluating unexplained thyrotoxicosis

Screening for Associated Autoimmune Conditions

Given high prevalence of polyautoimmunity, consider screening:

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7. Management

The goal of management is to restore and maintain euthyroidism, alleviate symptoms, prevent complications, and identify high-risk situations (especially pregnancy).

Indications for Treatment

Overt Hypothyroidism

Treat all patients with:

• TSH > 10 mU/L, regardless of Free T4 level [23]
• TSH 4.5-10 mU/L with low Free T4

Subclinical Hypothyroidism (TSH 4.5-10 mU/L, Normal Free T4)

Treat if ANY of the following:

1. Symptoms consistent with hypothyroidism
2. Positive Anti-TPO antibodies (high progression risk)
3. Pregnancy or attempting to conceive
4. Goitre causing compressive symptoms
5. Age less than 65-70 years with TSH persistently > 7-10 mU/L [24]
6. Dyslipidaemia (treatment may improve lipid profile)
7. Infertility or recurrent miscarriage

Monitor without treatment if:

• TSH 4.5-7 mU/L, asymptomatic, antibody-negative, not pregnant
• Repeat TFTs in 3-6 months to assess trend

Medical Therapy: Levothyroxine (T4 Replacement)

Pharmacology

• Levothyroxine sodium: Synthetic T4 (identical to endogenous thyroxine)
• Half-life: 7 days (allows once-daily dosing and steady state in 4-6 weeks)
• Bioavailability: 70-80% oral absorption (duodenum and jejunum)
• Peripheral conversion: T4 → T3 (more potent form) by deiodinase enzymes

Dosing Strategy

Initial Dose Calculation:

• Standard dose: 1.6 mcg/kg/day (approximates 100-125 mcg daily for most adults) [23]
• Typical starting doses:
  • "Young, healthy adults: 50-100 mcg daily (or full replacement dose)"
  • Elderly (> 60-65 years): 25-50 mcg daily ("start low, go slow")
  • "Ischaemic heart disease or arrhythmia: 12.5-25 mcg daily (titrate cautiously to avoid precipitating angina or AF)"

Exam Detail: Rationale for Age-Based Dosing:

• Elderly patients have decreased metabolic clearance of thyroid hormones
• Rapid correction in elderly or cardiac patients risks:
  • Acute coronary syndrome (increased myocardial oxygen demand)
  • Atrial fibrillation (thyroid hormones increase atrial automaticity)
  • Worsening heart failure (increased cardiac work)

Special Dosing Scenarios:

• Pregnancy: Increase dose by 25-30% (or add 2 extra weekly doses) immediately upon confirmation [7]
• Post-myocardial infarction: Delay treatment for 2-4 weeks if possible; start 12.5-25 mcg if essential
• Malabsorption (coeliac disease, PPI use): May require 20-30% higher dose

Administration

Timing:

• Optimal: First thing in morning, 30-60 minutes before breakfast, with water
• Maintains consistent absorption and avoids food interference

Drug and Food Interactions (reduce absorption):

Drugs Increasing Levothyroxine Requirement:

• Rifampicin: Induces hepatic metabolism
• Phenytoin, carbamazepine, phenobarbital: Enzyme induction
• Oestrogen (HRT, OCP): Increases thyroxine-binding globulin
• Tyrosine kinase inhibitors: Increased metabolism

Monitoring and Dose Titration

Initial Phase:

1. Check TSH and Free T4 6-8 weeks after starting or dose change (allows steady state)
2. Adjust dose in 12.5-25 mcg increments based on results
3. Repeat until TSH target achieved

Maintenance Phase:

• Check TSH annually once stable
• More frequent if dose change, pregnancy, significant weight change, or new medications

Target TSH:

• General population: 0.5-2.5 mU/L (or within local reference range, 0.4-4.0 mU/L) [23]
• Pregnancy: less than 2.5 mU/L in 1st trimester; less than 3.0 mU/L in 2nd and 3rd trimesters [7]
• Elderly (> 70 years): 1.0-4.0 mU/L (avoid overtreatment risk)
• Post-thyroid cancer: 0.1-0.5 mU/L (suppressive therapy)

Exam Detail: Why TSH Takes 6-8 Weeks to Stabilize:

• Levothyroxine half-life is 7 days
• Steady state achieved after 4-5 half-lives = 28-35 days
• Pituitary TSH response lags behind peripheral thyroid hormone levels
• Do NOT check TSH sooner than 6 weeks after dose change (will be misleading)

Persistent Symptoms Despite Normal TSH:

• Ensure compliance (missed doses)
• Check timing of administration (food/drug interactions)
• Verify absorption (coeliac disease, PPI use)
• Consider alternative diagnoses (depression, anaemia, sleep apnoea)
• Liothyronine (T3) combination therapy is NOT routinely recommended (no proven benefit in trials) [25]

Special Populations

Pregnancy and Preconception

Thyroid hormone is critical for fetal neurodevelopment in the first trimester (fetus relies entirely on maternal T4 until 10-12 weeks when fetal thyroid develops).

Preconception:

• Optimize TSH to less than 2.5 mU/L before conception [7]
• Women with Anti-TPO antibodies have increased miscarriage risk even if euthyroid; consider treatment if TSH > 2.5 mU/L

During Pregnancy:

1. Immediately increase levothyroxine dose by 25-30% upon confirmation of pregnancy (e.g., add 2 extra weekly doses)
2. Check TSH every 4 weeks in 1st and 2nd trimester; every 6-8 weeks in 3rd trimester
3. Target TSH less than 2.5 mU/L (1st trimester), less than 3.0 mU/L (2nd and 3rd trimester)
4. Postpartum: Reduce dose to pre-pregnancy level; check TSH at 6 weeks

Rationale:

• Pregnancy increases levothyroxine requirement by 30-50% due to:
  • Increased thyroxine-binding globulin (oestrogen effect)
  • Increased metabolic rate and glomerular filtration
  • Placental deiodinase activity
  • Increased maternal-fetal transfer

Elderly Patients

• Start low dose: 12.5-25 mcg daily
• Titrate slowly: Increase by 12.5-25 mcg every 6-8 weeks
• Target TSH: 1.0-4.0 mU/L (avoid overtreatment)
• Monitor cardiovascular status: Watch for angina, palpitations, AF

Patients with Ischaemic Heart Disease

• Very cautious approach: Risk of precipitating acute coronary syndrome or arrhythmia
• Start 12.5-25 mcg daily
• Increase by 12.5 mcg every 4-6 weeks
• Liaise with cardiology if unstable angina or recent MI
• Consider delaying treatment if very recent MI (less than 4 weeks)

Subclinical Hypothyroidism in Elderly (> 65-70 years)

• TSH 4.5-7 mU/L: Generally do NOT treat unless symptomatic [24]
• TSH 7-10 mU/L: Consider treatment on individual basis (balance benefits vs risks)
• TSH > 10 mU/L: Treat

Rationale: Overtreatment in elderly increases risk of atrial fibrillation, osteoporosis, and fractures; mild TSH elevation may be physiological with aging.

Management of Hashitoxicosis (Transient Hyperthyroidism)

• Self-limiting (2-8 weeks); destructive release of pre-formed hormone
• Beta-blockers (propranolol 10-40 mg TDS or atenolol 25-50 mg OD) for symptomatic relief (palpitations, tremor, anxiety)
• Do NOT use antithyroid drugs (carbimazole, propylthiouracil)—these are ineffective as thyroid is not actively synthesizing hormone
• Monitor TSH/Free T4 every 4-6 weeks as patient will progress to hypothyroidism
• Start levothyroxine when TSH rises

Surgical Management

Indications for Thyroidectomy (rare):

1. Compressive symptoms: Dysphagia, dyspnoea, stridor (retrosternal goitre)
2. Suspected malignancy: Dominant nodule with suspicious cytology
3. Cosmetic concerns: Large goitre causing neck disfigurement (patient request)
4. Primary thyroid lymphoma: Total thyroidectomy may be part of treatment

Post-thyroidectomy:

• Lifelong levothyroxine replacement
• Higher doses required (no residual thyroid tissue)
• Monitor calcium (risk of hypoparathyroidism)

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8. Complications

Disease-Related Complications

Myxoedema Coma

Most severe, life-threatening complication of hypothyroidism; mortality 20-40% even with treatment [26].

Definition: Severe hypothyroidism with altered mental status and hypothermia.

Triggers:

• Infection (pneumonia, UTI)
• Cold exposure
• Medications (sedatives, anaesthetics, opioids)
• Acute illness (MI, stroke, trauma)
• Stopping levothyroxine therapy

Clinical Features:

• Hypothermia: Core temperature less than 35°C
• Altered mental status: Confusion, lethargy, coma (GCS less than 8)
• Bradycardia: HR less than 50 bpm
• Hypotension: Cardiovascular collapse
• Hypoventilation: Respiratory failure, hypercapnia (pCO₂ > 45 mmHg)
• Hyponatraemia: Severe (Na less than 120 mmol/L)
• Hypoglycaemia: Possible

Management (ICU/HDU setting):

1. IV Levothyroxine loading dose: 200-400 mcg IV, then 50-100 mcg IV daily [26]
2. IV Liothyronine (T3): 5-20 mcg IV bolus, then 2.5-10 mcg every 8 hours (faster onset than T4)
3. IV Hydrocortisone: 100 mg IV every 8 hours (cover possible co-existent adrenal insufficiency until ruled out)
4. Passive rewarming: Avoid active rewarming (risk of vasodilation and cardiovascular collapse)
5. Mechanical ventilation: If hypoventilation or pCO₂ rising
6. Treat precipitant: Antibiotics for infection, etc.
7. Avoid sedatives: Extreme sensitivity in hypothyroid patients

Primary Thyroid Lymphoma

Hashimoto's thyroiditis confers 40-80 fold increased risk of primary thyroid lymphoma (most commonly MALT lymphoma, diffuse large B-cell lymphoma). [8]

Suspect if:

• Rapidly enlarging goitre over weeks to months
• Hard, fixed thyroid mass
• Compressive symptoms (dysphagia, dyspnoea, hoarseness)
• Cervical lymphadenopathy
• B symptoms (fever, night sweats, weight loss)

Diagnosis:

• Urgent ultrasound and FNA/core biopsy
• Immunohistochemistry and flow cytometry
• Staging CT/PET-CT

Management:

• Haematology/oncology referral
• Chemotherapy ± radiotherapy ± surgery (depending on stage and type)

Cardiovascular Complications

• Dyslipidaemia: Increased LDL-cholesterol and total cholesterol
• Atherosclerotic cardiovascular disease: Increased risk of coronary artery disease, stroke [6]
• Heart failure: Diastolic dysfunction; rare dilated cardiomyopathy
• Pericardial effusion: Usually asymptomatic; rarely causes tamponade

Reproductive Complications

• Infertility: Anovulation; hyperprolactinaemia
• Recurrent miscarriage: 2-4 fold increased risk [7]
• Adverse pregnancy outcomes (if untreated):
  • Preterm birth
  • Pre-eclampsia
  • Placental abruption
  • Postpartum haemorrhage
  • "Fetal/neonatal: Impaired neurodevelopment, low birth weight, stillbirth"

Neuropsychiatric Complications

• Depression: Bidirectional relationship (hypothyroidism causes depression; depression may mimic hypothyroidism)
• Cognitive impairment: Memory deficits, slowed processing
• Myxoedema madness: Psychosis (rare)
• Cerebellar ataxia: Rare complication

Hashimoto's Encephalopathy (Steroid-Responsive Encephalopathy)

Rare, controversial condition associated with high Anti-TPO antibodies (usually > 1000 IU/mL) and neurological symptoms.

Features:

• Encephalopathy (confusion, seizures, myoclonus, stroke-like episodes)
• Usually euthyroid or mildly hypothyroid
• High Anti-TPO titres
• Responds to high-dose corticosteroids

Diagnosis: Exclusion of other causes; EEG, MRI brain, CSF analysis

Treatment: IV methylprednisolone 1g daily for 3-5 days, then oral prednisolone taper

Treatment-Related Complications

Over-Replacement (Iatrogenic Thyrotoxicosis)

Causes:

• Excessive levothyroxine dose
• Intentional or accidental overdose
• Weight loss (dose now excessive for body weight)

Clinical Features:

• Palpitations, tremor, anxiety
• Weight loss
• Heat intolerance
• Insomnia

Complications of Chronic Over-Replacement:

• Atrial fibrillation: Especially in elderly
• Osteoporosis and fractures: Increased bone resorption (postmenopausal women at highest risk) [27]
• Cardiovascular events: Increased risk of MI, stroke

Management:

• Reduce levothyroxine dose
• Check TSH in 6-8 weeks
• Target physiological TSH (avoid suppression unless post-cancer)

Under-Replacement

Causes:

• Non-compliance
• Inadequate dose
• Malabsorption (coeliac disease, PPI use)
• Drug interactions

Consequences:

• Persistent hypothyroid symptoms
• Cardiovascular risk
• Pregnancy complications

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9. Prognosis and Outcomes

Natural History

Untreated:

• Progressive thyroid destruction and worsening hypothyroidism
• Increased cardiovascular morbidity and mortality
• Impaired quality of life

With Treatment:

• Excellent prognosis for most patients
• Return to normal function and quality of life within 3-6 months of achieving euthyroidism
• Lifelong treatment usually required (spontaneous remission rare, less than 5%)

Quality of Life

• Most patients (85-90%) achieve complete symptom resolution with levothyroxine monotherapy [23]
• 10-15% report persistent symptoms despite biochemically normal TSH:
  • Fatigue, cognitive slowing, weight issues
  • Mechanisms unclear (possible T3 deficiency in some tissues, psychological factors, co-morbidities)
  • "Combination T4/T3 therapy: Controversial; multiple RCTs show no consistent benefit over T4 monotherapy [25]"
  • Guidelines (NICE, ATA, BTA) do NOT recommend routine T3 use

Goitre Response

• Shrinks in 50-70% of patients with levothyroxine treatment (TSH suppression reduces thyroid stimulation)
• May take 6-12 months to see maximal reduction
• Large, long-standing goitres may not reduce significantly

Pregnancy Outcomes

• Excellent maternal and fetal outcomes if adequately treated and monitored [7]
• Emphasize importance of immediate dose increase upon pregnancy confirmation

Progression to Lymphoma

• Overall risk remains low (less than 0.5% lifetime risk)
• Vigilance for rapidly enlarging goitre essential

Life Expectancy

• Normal life expectancy if adequately treated
• Untreated or under-treated: Increased cardiovascular mortality

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10. Prevention and Screening

Primary Prevention

• Adequate iodine intake: 150 mcg/day for adults; 220-250 mcg/day in pregnancy [13]
• Avoid iodine excess: Excessive supplementation or iodine-containing medications may trigger autoimmunity
• Selenium supplementation: Controversial; may reduce Anti-TPO titres in some studies but does not prevent disease [13]

Screening

General Population:

• NOT recommended for asymptomatic adults (low yield, unclear benefit)

High-Risk Groups (Consider Screening):

1. Women planning pregnancy or in early pregnancy (especially if family history or previous thyroid disease)
2. Postpartum women with previous postpartum thyroiditis or Type 1 diabetes (high recurrence risk)
3. Patients with other autoimmune diseases (Type 1 diabetes, Coeliac disease, Addison's disease)
4. First-degree relatives of patients with autoimmune thyroid disease
5. Patients on amiodarone, lithium, or checkpoint inhibitors (immune-related adverse events)
6. Down syndrome and Turner syndrome (increased prevalence)

Screening Test: Serum TSH ± Free T4 ± Anti-TPO antibodies

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11. Key Guidelines and Evidence

Major Society Guidelines

Landmark Evidence

1. Levothyroxine dosing: 1.6 mcg/kg/day achieves target TSH in most patients [23]
2. T4/T3 combination therapy: Multiple RCTs (Cochrane review) show no benefit over T4 monotherapy for quality of life [25]
3. Pregnancy: Maternal hypothyroidism (even subclinical) associated with impaired fetal neurodevelopment if untreated [7]
4. Subclinical hypothyroidism: Treatment beneficial if TSH > 10 mU/L or Anti-TPO positive [24]

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12. Examination Focus

Common Viva Questions

Viva Point: Q1: "What is Hashimoto's thyroiditis?"

Model Answer: "Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is an organ-specific autoimmune disease and the most common cause of hypothyroidism in iodine-sufficient regions. It is characterised by lymphocytic infiltration of the thyroid gland, progressive destruction of thyroid follicles, and the presence of anti-thyroid antibodies—particularly Anti-TPO antibodies in over 90% of cases. The condition has a strong female predominance with a 7:1 to 15:1 female-to-male ratio and typically presents in the 30-50 age group. Patients develop progressive hypothyroidism requiring lifelong levothyroxine replacement."

Viva Point: Q2: "How would you investigate a patient presenting with symptoms of hypothyroidism?"

Model Answer: "I would adopt a systematic approach. First-line investigation is serum TSH, which is the most sensitive screening test for primary hypothyroidism. If TSH is elevated, I would check Free T4 to distinguish between subclinical hypothyroidism—where TSH is raised but Free T4 is normal—and overt hypothyroidism where both TSH is elevated and Free T4 is low. To confirm an autoimmune aetiology, I would check Anti-Thyroid Peroxidase antibodies, which are positive in over 90% of Hashimoto's cases. Supportive tests include lipid profile, which often shows hypercholesterolaemia, creatine kinase which may be elevated, and full blood count to look for anaemia. If there is a palpable nodule or asymmetric thyroid enlargement, I would arrange a thyroid ultrasound and consider fine-needle aspiration if indicated."

Viva Point: Q3: "How would you manage a 35-year-old woman with newly diagnosed hypothyroidism due to Hashimoto's thyroiditis?"

Model Answer: "Management centres on levothyroxine replacement. In a young, healthy woman, I would start levothyroxine at a dose of approximately 1.6 micrograms per kilogram per day, which typically equates to 100-125 micrograms daily. I would advise her to take it first thing in the morning, 30-60 minutes before breakfast, with water, to ensure optimal absorption. I would counsel her on drug interactions—particularly calcium, iron, and proton pump inhibitors, which should be separated by at least four hours. I would arrange follow-up thyroid function tests in 6-8 weeks to assess response and adjust the dose if necessary, aiming for a TSH between 0.5 and 2.5 milliunits per litre. Once stable, annual monitoring of TSH is appropriate. Importantly, if she is planning pregnancy or becomes pregnant, she should inform me immediately as the levothyroxine dose will need to be increased by 25-30% and TSH should be kept below 2.5 in the first trimester to ensure optimal fetal neurodevelopment. I would also screen for associated autoimmune conditions such as coeliac disease and pernicious anaemia given the polyautoimmune associations."

Viva Point: Q4: "What is myxoedema coma and how would you manage it?"

Model Answer: "Myxoedema coma is a life-threatening endocrine emergency representing severe decompensated hypothyroidism with altered mental status and hypothermia. It has a mortality rate of 20-40% even with treatment. Triggers include infection, cold exposure, medications such as sedatives, and acute illness. Clinical features include core temperature below 35 degrees Celsius, altered mental status ranging from confusion to coma with a GCS less than 8, severe bradycardia, hypotension, hypoventilation with hypercapnia, and often severe hyponatraemia. Management requires ICU admission. I would give intravenous levothyroxine as a loading dose of 200-400 micrograms followed by 50-100 micrograms daily. I would also administer intravenous liothyronine—T3—which has a faster onset of action, at a dose of 5-20 micrograms bolus then 2.5-10 micrograms every 8 hours. Critically, I would give intravenous hydrocortisone 100 milligrams every 8 hours to cover possible co-existent adrenal insufficiency until this is ruled out. Supportive measures include passive rewarming to avoid cardiovascular collapse, mechanical ventilation if needed for hypoventilation, and treating the precipitant such as infection with antibiotics. Sedatives must be avoided due to extreme sensitivity in hypothyroid patients."

Common Mistakes to Avoid

❌ Failing to recognize subclinical hypothyroidism in pregnancy: Even mildly elevated TSH (> 2.5 mU/L) in pregnancy requires treatment to prevent fetal harm.

❌ Checking TSH too soon after dose change: TSH takes 6-8 weeks to stabilize; earlier testing is misleading.

❌ Starting full-dose levothyroxine in elderly or cardiac patients: Risk of precipitating acute coronary syndrome or atrial fibrillation; start low (12.5-25 mcg) and titrate slowly.

❌ Overlooking drug interactions: Calcium, iron, and PPIs significantly reduce levothyroxine absorption.

❌ Failing to increase levothyroxine in pregnancy: Dose needs to increase by 25-30% immediately upon confirmation.

❌ Using antithyroid drugs for Hashitoxicosis: This is a destructive process (hormone release), not active synthesis; use beta-blockers for symptom control only.

❌ Missing rapidly enlarging goitre: This is a red flag for thyroid lymphoma requiring urgent investigation.

❌ Routine use of T3 combination therapy: Not supported by evidence; should not be offered routinely.

Examination Pearls

✅ Delayed relaxation of ankle jerks (Woltman's sign): Highly specific clinical sign of hypothyroidism.

✅ Anti-TPO antibodies > 90% sensitive: Gold standard for confirming autoimmune aetiology.

✅ 1.6 mcg/kg/day levothyroxine: Standard replacement dose for most adults.

✅ Pregnancy: TSH less than 2.5 in 1st trimester: Critical for fetal neurodevelopment.

✅ Hashimoto's increases thyroid lymphoma risk 40-80 fold: Vigilance for rapid goitre growth.

✅ Myxoedema coma requires IV T4 + IV T3 + IV hydrocortisone: Cover co-existent adrenal insufficiency.

✅ Polyautoimmunity: Screen for Type 1 diabetes, coeliac disease, pernicious anaemia, Addison's disease.

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13. Patient and Layperson Explanation

What is Hashimoto's Thyroiditis?

Hashimoto's thyroiditis is a condition where your body's immune system—which normally fights infections—mistakenly attacks your thyroid gland. Your thyroid is a small butterfly-shaped gland in your neck that produces hormones controlling your body's metabolism (how your body uses energy). Over time, this immune attack damages the thyroid so it cannot make enough thyroid hormone, leading to an underactive thyroid or "hypothyroidism."

Why Does It Happen?

Hashimoto's is an autoimmune disease. Your immune system gets confused and starts attacking the thyroid as if it were a foreign invader. We don't fully understand why this happens, but it runs in families and is much more common in women than men. It is often associated with other autoimmune conditions like Type 1 diabetes or coeliac disease.

What Are the Symptoms?

Because thyroid hormone acts like your body's "accelerator pedal" for metabolism, a lack of it slows everything down. Common symptoms include:

• Extreme tiredness: Feeling exhausted even after a full night's sleep
• Weight gain: Gaining weight even though you're not eating more
• Feeling cold: Needing to wear extra layers when others are comfortable
• Dry skin and hair: Skin becomes dry and rough; hair may thin
• Constipation: Bowel movements become sluggish
• Brain fog: Difficulty concentrating and remembering things
• Low mood: Feeling down or depressed

Some people also develop a swelling in the neck called a goitre, which is the enlarged thyroid gland.

How Is It Diagnosed?

Your doctor will order a simple blood test to check:

1. TSH (Thyroid Stimulating Hormone): This goes up when your thyroid isn't working properly
2. Free T4 (thyroxine): This goes down when your thyroid is underactive
3. Anti-TPO antibodies: These are present in over 90% of people with Hashimoto's and confirm it's an autoimmune problem

How Is It Treated?

The good news is that Hashimoto's is very treatable. You will take a daily tablet called levothyroxine, which is an exact replacement for the thyroid hormone your body is no longer making. Most people feel much better within a few weeks to months of starting treatment.

How to take levothyroxine:

• Take it first thing in the morning, on an empty stomach
• Wait at least 30 minutes before eating breakfast
• Avoid taking it with calcium, iron supplements, or antacids (these interfere with absorption)

Your doctor will monitor your thyroid levels with blood tests every 6-8 weeks initially, then once a year once your dose is stable.

Will I Need to Take It Forever?

In most cases, yes—you will need to take levothyroxine for life. The immune damage to the thyroid is permanent, so your body cannot recover its ability to make thyroid hormone on its own. However, the tablet is very safe, has no serious side effects when taken at the correct dose, and allows you to live a completely normal, healthy life.

What If I Want to Get Pregnant?

Levothyroxine is completely safe during pregnancy—in fact, it is essential. Your developing baby relies on your thyroid hormone for brain development, especially in the first three months. If you are planning to get pregnant or find out you are pregnant, tell your doctor immediately because you will need a higher dose during pregnancy. With proper treatment and monitoring, you can have a healthy pregnancy and baby.

What Happens If I Don't Treat It?

Untreated hypothyroidism can lead to serious problems:

• Heart problems and high cholesterol
• Difficulty getting pregnant or increased risk of miscarriage
• Severe tiredness affecting quality of life
• In extreme cases, a life-threatening condition called "myxoedema coma"

Can I Prevent It?

Unfortunately, there is no proven way to prevent Hashimoto's if you are genetically predisposed. However, ensuring adequate iodine in your diet (through iodized salt, dairy products, and seafood) supports thyroid health.

Living Well with Hashimoto's

• Take your medication regularly: Consistency is key
• Attend follow-up appointments: Regular blood tests ensure your dose is correct
• Healthy lifestyle: Balanced diet, regular exercise, and adequate sleep support overall well-being
• Be aware of other conditions: Hashimoto's is linked to other autoimmune conditions, so mention any new symptoms to your doctor

Key Takeaway

Hashimoto's thyroiditis is a lifelong condition, but with daily levothyroxine replacement, you can live a completely normal, healthy, and active life. The most important thing is to take your medication consistently and have regular check-ups with your doctor.

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Document Metadata:

• Citation Count: 20 peer-reviewed PubMed sources
• Line Count: 1,205 lines
• Target Audience: Postgraduate medical trainees (MRCP, endocrinology candidates)
• Evidence Level: High (multiple systematic reviews, RCTs, international guidelines)
• Last Updated: 2026-01-06

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