Pneumocystis jirovecii pneumonia (PCP)

This page works the case through in full, answer included. If you would rather reason it out yourself: Play this case

How the diagnosis is reached

A chest that sounds normal has no business belonging to a man who desaturates crossing the corridor and whose room-air PaO₂ is 62 mmHg. That mismatch, profound hypoxia against an unremarkable examination, is the classic tell of Pneumocystis, and it is what separates this from the bacterial pneumonia six weeks of cough might otherwise suggest. Oral candidiasis with weight loss and night sweats points to underlying immunosuppression, and a CD4 count below 200 cells/µL is the threshold at which Pneumocystis becomes a real risk. A raised LDH is sensitive though non-specific, and beta-D-glucan supports the diagnosis. Radiographically, bilateral perihilar interstitial shadowing without effusion, cavitation or lymphadenopathy fits, and helps separate this from tuberculosis, which typically shows upper zone changes with cavitation. Treatment should never wait on bronchoalveolar lavage, because organism burden persists for days after therapy starts, so a sample taken later still yields the diagnosis. High-dose trimethoprim-sulfamethoxazole for 21 days is the treatment, given intravenously at this severity. The PaO₂ of 62 mmHg also settles the second decision: below 70 mmHg, or with an alveolar-arterial gradient above 35 mmHg, adjunctive corticosteroids improve survival. The reason is counterintuitive. Killing the organism releases antigen and provokes an inflammatory deterioration around day three, so patients get worse on effective treatment; steroids blunt that and are started with the antibiotic rather than in response to it. The negative AFB smear matters too, since tuberculosis is the other diagnosis a CD4 of 84 invites and steroids without cover would be the wrong move there.

Key clinical clues

• Marked exertional desaturation with an essentially normal chest examination
• Oral candidiasis, weight loss and night sweats indicating immunosuppression
• Raised LDH and beta-D-glucan with lymphopenia
• Bilateral perihilar interstitial change without effusion, cavitation or nodes
• CD4 of 84 cells/µL, below the threshold where this organism becomes a risk

The case in full

1

Presenting complaint

Patient history

A 34-year-old man reports six weeks of worsening breathlessness and a persistent dry cough. He can no longer manage one flight of stairs. He has lost 8 kg and has intermittent night sweats.

2

Examination

Physical examination

He has white plaques on the tongue and buccal mucosa that scrape off to leave a raw base. Chest auscultation is unremarkable. There is no lymphadenopathy or rash.

3

Oxygenation on exertion

Vital signs

Saturations are recorded at rest, then during a supervised walk along the corridor.

4

Laboratory results

Laboratory results

Bloods are sent, including a serum marker requested by the respiratory team.

Measurements

Parameter	Value	Reference
LDH	684 U/LRef 140–280	140–280
White blood cells	4.1 ×10⁹/LRef 4.5–11.0	4.5–11.0
Lymphocytes	0.5 ×10⁹/LRef 1.0–4.0	1.0–4.0
C-reactive protein	38 mg/LRef <5	<5
Beta-D-glucan	412 pg/mLRef <80	<80
PaO₂ (room air)	62 mmHgRef 80–100	80–100

5

Chest radiograph

Imaging

A chest radiograph is taken.

6

Further investigations

Laboratory results

A rapid point-of-care test and lymphocyte subsets are sent after counselling.

Measurements

Parameter	Value	Reference
HIV antigen/antibody	ReactiveRef Non-reactive	Non-reactive
CD4 count	84 cells/µLRef >500	>500
HIV viral load	412,000 copies/mLRef Not detected	Not detected
Sputum AFB smear	NegativeRef Negative	Negative