Pneumocystis Pneumonia (PCP)
Summary
Pneumocystis Pneumonia (PCP), now technically Pneumocystis jirovecii Pneumonia (PJP), is a life-threatening fungal infection affecting immunocompromised hosts. It is the most common AIDS-Defining Illness. It also affects non-HIV patients on immunosuppression (chemotherapy, steroids). It presents as a progressive exertional dyspnoea with a non-productive cough. [1,2]
Clinical Pearls
The "Silent Chest": A classic exam finding. The patient is hypoxic and breathless, but when you listen to the chest, it sounds completely normal (no crackles/wheeze). This is because the pathology is interstitial, not alveolar filling.
Exercise Desaturation: If you suspect PCP in a patient with normal resting sats, walk them up and down the corridor. If sats drop from 98% to 92%, this is highly suggestive.
Steroids Save Lives: In severe PCP (Hypoxia pO2 less than 9.3 kPa), the dying fungus releases inflammatory antigens causing a "cytokine storm" that worsens respiratory failure. Giving steroids before or with antibiotics suppresses this reaction and reduces mortality by 50%.
Risk Factors
- HIV/AIDS: CD4 count < 200 cells/µL.
- Malignancy: Haematological (Leukaemia/Lymphoma).
- Transplant: Solid organ or Stem Cell recipients.
- Drugs: High dose steroids (>20mg Prednisolone for >4 weeks), Methotrexate, Anti-TNF agents.
Organism
- Pneumocystis jirovecii (formerly carinii).
- Classified as a fungus but shares biological properties with protozoa.
- Cannot be cultured.
Mechanism
- Inhaled trophic forms attach to Type I pneumocytes.
- Proliferate into cysts.
- Cause diffuse alveolar damage + interstitial inflammation.
- Thickened alveolar-capillary barrier blocks gas exchange -> Hypoxia.
Symptoms
Signs
- General: Looking for stigma of HIV/Immunosuppression (Oral Thrush, KS lesions, lymphadenopathy).
- Vitals: Oxygen saturation at rest AND exertion.
Imaging
- CXR:
- Normal (10-15%).
- Perihilar Interstitial Infiltrates ("Bat's Wing" appearance).
- Reticulonodular shadowing.
- HRCT Chest: Gold standard imaging. "Ground Glass Opacification" (100% sensitivity - if CT is normal, it is NOT PCP). cysts/pneumatoceles may be seen.
Microbiology
- Sputum: Induced sputum (nebulised hypertonic saline). Stain with Silver stain or Immunofluorescence.
- Bronchoalveolar Lavage (BAL): Gold standard diagnostic test (Sensitivity >90%).
- PCR: Highly sensitive but can't distinguish colonization from infection.
Bloods
- ABG: Essential to stratify severity (A-a gradient is widened).
- LDH: Elevated (>500 IU/L) in >90% of HIV-PCP (Tissue damage marker).
- Beta-D-Glucan: High negative predictive value (If negative, exclude PCP).
Management Algorithm
SUSPECTED PCP
(Hypoxia, Dry Cough, CD4 less than 200)
↓
ASSESS SEVERITY (ABG)
Mild: pO2 > 11 kPa
Mod: pO2 9.3 - 11 kPa
Sev: pO2 < 9.3 kPa
↓
START TREATMENT (Empiric)
Don't wait for bronchoscopy
High Dose Co-trimoxazole
↓
SEVERE HYPOXIA? (less than 9.3 kPa)
┌─────────┴─────────┐
YES NO
↓ ↓
ADD STEROIDS ANTIBIOTICS
(Prednisolone) ALONE
40mg BD x 5d
Pharmacotherapy
- First Line: Co-trimoxazole (Trimethoprim-Sulfamethoxazole / Septrin).
- Dose: High dose (120mg/kg/day) in divided doses.
- Route: IV if severe, Oral if mild.
- Duration: 21 days.
- Second Line (Sulpha Allergy or Failure):
- Clindamycin + Primaquine.
- Pentamidine (IV).
- Atovaquone (Mild cases).
Adjuvant Steroids
- Indication: pO2 < 9.3 kPa (70 mmHg) or A-a gradient > 35 mmHg.
- Dose: Prednisolone 40mg BD x 5 days, then 40mg OD x 5 days, then 20mg OD x 11 days.
- Pneumothorax: Rupture of pneumatocele (cysts). Difficult to treat (bronchopleural fistula).
- Respiratory Failure: ARDS.
- Drug Toxicity: Bone marrow suppression, Rash (Stevens-Johnson), Nephrotoxicity (Pentamidine).
- HIV-PCP: Mortality 10-20%.
- Non-HIV PCP: Mortality 30-60% (diagnostic delay and lower inflammatory reserve).
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| HIV Guidelines | BHIVA / EACS | Primary prophylaxis (Septrin) if CD4 less than 200. Treat for 21 days. |
| Pneumonia | BTS | Consider PCP in any immunocompromised patient. |
Landmark Evidence
1. The steroid trials (NEJM 1990)
- Consensus statement confirming adjunctive corticosteroids halve the mortality in severe PCP.
What is PCP?
It is a serious lung infection caused by a fungus that lives in the environment. Most healthy people have encountered it and cleared it without knowing. It only causes pneumonia in people with very weak immune systems (like HIV or cancer patients).
What are the symptoms?
A dry cough and shortness of breath that gets worse over weeks. You might feel fine sitting down but gasp for air after walking to the bathroom.
How is it treated?
High doses of an antibiotic called Co-trimoxazole (Septrin) for 3 weeks. If your oxygen levels are very low, we also give steroids to calm the inflammation in your lungs.
Is it contagious?
Technically yes, but only to other people with weak immune systems. You cannot catch it from someone if your immune system is normal.
Primary Sources
- BHIVA. Guidelines for the management of opportunistic infections in people living with HIV. 2020.
- Masur H, et al. Consensus statement on the use of corticosteroids as adjunctive therapy for pneumocystis pneumonia in the acquired immunodeficiency syndrome. N Engl J Med. 1990.
Common Exam Questions
- Investigation: "Ground glass opacities on CT?"
- Answer: PCP.
- Management: "Hypoxic PCP patient - add what?"
- Answer: Steroids (Prednisolone).
- Diagnosis: "Desaturation on exertion with normal chest sounds?"
- Answer: PCP.
- Stain: "Silver stain positive?"
- Answer: Pneumocystis jirovecii.
Viva Points
- Prophylaxis: Who gets it? Anyone with CD4 < 200. Co-trimoxazole 480mg or 960mg OD/MWF. It also protects against Toxoplasmosis.
- Pentamidine: Side effects? Severe hypotension (give lying down), hypoglycaemia, pancreatitis.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.