Review Question - QID 103607

This patient presents with Pneumocystis pneumonia (PCP) which causes a diffuse interstitial pneumonia in immunocompromised hosts, typically with CD4+ counts < 200. It is characterized on histology by disc-shaped yeast as shown in Figure A.

Pneumocystis jirovecii is an opportunistic mycosis which causes PCP in immunocompromised hosts. While many infections are asymptomatic, those that are symptomatic often present with a subtle onset of dyspnea on exertion, non-productive cough, and low grade fever. On chest radiograph, diffuse interstitial infiltrates will be observed (Figure F), and chest CT scan can show ground glass opacities (Illustration A). On labs, patients will often have a lower PO2 than would be expected based on their clinical symptoms and a peripheral eosinophilia (Illustration B). Elevated LDH can also be observed. Diagnosis is made definitely by lung biopsy or lavage which yields the classic disc-shaped yeast forms on methenamine silver stain (Figure A). Prophylaxis for HIV patients should begin with TMP-SMX when CD4 count falls below 200.

Chu and Selwyn review the diagnosis and management of the complications and opportunistic infections observed in HIV patients. They state patients with human immunodeficiency virus (HIV) infection often develop multiple complications and comorbidities. Opportunistic infections should always be considered in the evaluation of symptomatic patients with advanced HIV/AIDS, although the overall incidence of these infections has decreased. Primary care of HIV infection includes the early detection of complications through screening at-risk and symptomatic patients with routine laboratory monitoring (e.g., comprehensive metabolic and lipid panels) and validated tools (e.g., the HIV Dementia Scale).

Esteves et al. assessed the usefulness of (1-3)-ß-d-glucan (BG), Krebs von den Lungen-6 antigen (KL-6), lactate dehydrogenase (LDH), and S-adenosyl methionine (SAM) as serologic biomarkers in the diagnosis of PCP. They found that the BG/KL-6 combination test was the most accurate serologic approach for PCP diagnosis, with 94.3% sensitivity and 89.6% specificity. Although less sensitive/specific than the reference standard classic methods based on bronchoalveolar lavage followed by microscopic or molecular detection of P. jirovecii organisms, the BG/KL-6 test may provide a less onerous procedure for PCP diagnosis, as it uses a minimally invasive and inexpensive specimen (blood), which may be also a major benefit for the patient's care.

Figures are described in the Incorrect Answer choice explanations below. Illustration A is a CT scan demonstrating the ground glass opacities that can be observed in PCP. Illustration B demonstrates eosinophilia which can occasionally be observed on a peripheral smear in PCP.

Incorrect Answers:
Answer 2: Figure B demonstrates Candida albicans which can causes systemic or superficial infections. In immunocompromised patients it typically causes oral and esophageal thrush. Note the pseudohyphae and budding yeast.

Answer 3: Figure C demonstrates Aspergillus fumigatus which typically presents as invasive aspergillosis in immunocompromised patients. Note the typical conidiophore with radiating chains of spores.

Answer 4: Figure D demonstrates Mucor, which is a fungal infection typically presenting in ketoacidotic diabetic and leukemic patients. Note the irregular, broad, non-septate hyphae branching at wide angles.

Answer 5: Figure E demonstrates histoplasmosis which can cause pneumonia in immunocompetent patients and is typically endemic in the Mississippi and Ohio river valleys. Note the macrophage filled with Histoplasma on histology.