12th January 2024

Pneumocystis Pneumonia (PCP)

Background

Pneumocystis pneumonia (PCP) is a potentially life-threatening condition caused by the fungus Pneumocystis jirovecii (previously called Pneumocystis Carinii). PCP predominantly affects immunocompromised individuals, and it remains a leading AIDS-defining opportunistic infection in individuals infected with HIV.

Presentation

PCP usually occurs in individuals who are known to be immunocompromised, yet it may also be the first presentation of an underlying condition such as HIV.

Symptoms of PCP include:

• Progressive shortness of breath
• Cough, which is usually dry
• Fever
• Chest pain
• Decreasing exercise tolerance

Signs on respiratory examination are variable and can be normal. Patients may have fine crackles on auscultation. Measuring oxygen saturations during mobilisation can be very useful, as patients with PCP will classically demonstrate a drop in saturations on exertion.

Symptoms and signs of HIV should also be assessed if PCP is suspected; weight loss, lymphadenopathy or evidence of thrush or Kaposi’s sarcoma would all raise suspicion for underlying HIV.

Investigations

Patients with PCP usually have multiple tests performed before a diagnosis is confirmed. If PCP is suspected, blood tests to consider include:

• Inflammatory markers (WCC, CRP)
• HIV testing
• Lactate dehydrogenase – if elevated, this is indicative of PCP and can also be used to predict inpatient mortality in PCP patients
• β-D-Glucan – part of the fungal cell wall and therefore can be used in diagnosis (this should be discussed with the microbiology or respiratory team before requesting).

Chest X-rays in PCP can be normal but typically show diffuse bilateral peri-hilar interstitial infiltrates. A subsequent high resolution CT chest can be helpful.

Pneumocystis jirovecii cannot be routinely cultured but can be detected by staining the cyst wall using silver-based stains or by polymerase chain reactions. Repeated sputum samples may need to be taken to confirm the diagnosis. Bronchoalveolar lavage may be required to acquire samples if the patient is unable to expectorate or if their sputum is negative.

Image Source: Wikimedia Commons (2010). CT of infiltrates of pneumocystis pneumonia, Licensed under a creative commons licence. Available for free at: https://upload.wikimedia.org/wikipedia/commons/3/32/CT_of_infiltrates_of_pneumocystis_pneumonia.jpg (Accessed: 1 March 2022).

Management

High-dose co-trimoxazole is the first line management in PCP and can be given by mouth or as an intravenous infusion. In patients who cannot tolerate co-trimoxazole, alternatives in mild-to-moderate PCP include atovaquone, a combination of dapsone and trimethoprim, or a combination of clindamycin and primaquine; of these, only atovaquone is licensed for this indication in the United Kingdom.

In severe PCP, in which patients have breathlessness at rest or a PₐO₂ <8 kPa/SₐO₂ <91%, IV pentamidine isethionate is an alternative for patients who cannot tolerate co-trimoxazole or who have not responded to it.

Corticosteroids are given as an adjunct in patients with moderate or severe PCP associated with HIV and can be life-saving in severe PCP. Oral prednisolone or parenteral hydrocortisone can be used, and they are usually given in high dosage for 5 days before the dose is reduced to complete a 21-day course.

Prophylaxis against PCP should be given to all patients with a history of the infection and also for severely immunocompromised patients (in HIV-positive individuals, this is once their CD4 T-cell count falls below 200 cells/mm³). Oral co-trimoxazole is the drug of choice for prophylaxis.

Complications

Pneumothorax is a common complication seen in PCP, with a prevalence ranging from 13-61% in PCP patients in various studies.

Additional complications of PCP include:

• Respiratory failure
• Extra-pulmonary infection
• Acute respiratory distress syndrome (ARDS)