Makindo Medical Notes

Related Subjects: |Adrenal Physiology |Addison's Disease

About Histoplasmosis

• Caused by the dimorphic fungus Histoplasma capsulatum.
• Found in soil contaminated with bat or bird droppings, particularly in the USA's midwestern and south-central river valleys and some parts of Eastern Europe.
• People at higher risk include cavers, bird handlers, and those cleaning areas with bat or bird droppings.

Aetiology

• Infection creates calcified fibrinous granulomas with caseous necrosis.
• Initial pulmonary infections can spread systemically, particularly in immunocompromised individuals.

Risk of Disseminated Infection

• AIDS patients with a CD4 count <150 cells/μL.
• Patients using corticosteroids, tumor necrosis factor (TNF) antagonists (e.g., etanercept, infliximab).
• People with hematologic malignancies or recent solid organ transplants.

Clinical Features

• Most exposures are asymptomatic, though clinical infections are more likely in immunocompromised individuals.
• Initial infection symptoms appear after 2-3 weeks, including fever, malaise, and erythema nodosum.
• Chronic infection may occur in male smokers, especially those with COPD, with features like fibrosing mediastinitis, which may obstruct the superior vena cava (SVC).
• Histoplasmosis can cause adrenal failure, and in disseminated cases, symptoms may include pancytopenia, hepatomegaly, and lymphadenopathy.

Investigations

• CXR/CT Imaging: Shows bihilar lymphadenopathy, fibrosis, cyst formation, and sometimes nodules of pulmonary calcification.
• Adrenal Function Tests: Cortisol levels and Short Synacthen test can indicate hypoadrenalism in affected patients.
• Blood Cultures: Useful in disseminated histoplasmosis.
• Serology: Tests for Anti-M and Anti-G glycoprotein antibodies, although false positives may occur (e.g., in lymphoma, tuberculosis, or sarcoidosis).
• Antigen Detection: Serum and urine antigen tests are beneficial in diagnosing disseminated cases.

Management

• Treatment varies by severity: mild cases often resolve spontaneously.
• For moderate to severe cases, antifungal therapy with Itraconazole or Amphotericin B may be required.
• Prolonged treatment may be needed in cases of disseminated infection or in immunocompromised patients.