Pathophysiology
1) caused by infection with opportunistic fungi Pneumocystis carinii 2) main habitat is the lung but can have systemic spread to lymph nodes, bone marro, liver, and spleen 3) exists in trophozoite (asexual reproduction), precyst, and cyst (sexual reproduction) forms
Signs and Symptoms
1) fever 2) dyspnea 3) nonproductive cough (i.e, dry cough) 4) tachypnea 5) tachycardia
Characteritistic Test Findings
Laboratory – 1) hypoxia 2) increased alveolar-arterial gradient (A-a gradient) 3) respiratory alkalosis 4) increased LDH 5) diagnosis is on identification of organism under histopathologic staining (toluidine blue, methanamine silver, and cresyl violet) Radiology – 6) classic finding on chest radiograph is bilateral diffuse infiltrates beginning in perihilar nodes (but can also have nodular densities and cavitary lesions
Histology/Gross Pathology
1) alveoli with foamy, vacuolated exudates, interstitial edema, hyaline membrane formation, and fibrosis 2) plasma cell infiltrates in malnourished patients
Associated Conditions
1) HIV 2) immunosuppressive therapy (esp. glucocorticoids) 3) cancer patients 4) malnourished premature infants 5) primary immunodeficiency disorder 6) use of aerosolized pentamidine causes increase pneumothorax, upper lobe infiltrates, and disseminated disease
Biochemistry
1) prominent antigen groups are major surface glycoproteins 2) organism lacks ergosterol (unlike most fungi that do contain this substance) 3) prinicipal host defense is alveolar macrophages 4) after inhalation, organism attaches to type 1 lung cells and type 2 lung cells hypertrophy 5) decreased bronchoalveolar lavage fluid and increased surfactant proteins A and D
Inheritance/Epidemiology
1) worldwide distribution 2) most children are exposed by age 3 years 3) incubation is 4-8 weeks 4) transmission is via inhalation
Treatment
1) trimethoprim-sulfamethoxazole (Bactrim) which inhibits folic acid synthesis 3-4 times/dau for 220 days 2) if Bactrim side effects are too severe can try trimethoprim and dapsone or clindamycin and primaquine or atovaquone 3) in very severe cases can try pentamidine IV or aerosol or trimetrexate and folinic acid 4) in moderate to severe disease, glucocorticoids are used in first 2 weeks of treatment to prevent the initial worsening with anti-Pneumocystis therapy 5) prophylactic treatment for high-risk patients is a low dose of trimethoprim-sulfamethoxazole daily
Tips for USMLE
1) traditional antifungal drugs are not effective against Pneumocystis 2) laboratory abnormalities are less pronounced in HIV related pneumocystis than non-HIV related pneumocystis
Leave a Reply