Makindo Medical Notes.com

Related Subjects: |Adrenal Physiology |Addisons Disease

About

• Infection due to dimorphic fungus Histoplasma capsulatum
• Carried in bat (avoid caves) and bird and spread by droppings onto the soil
• May be found in the soil in endemic areas of the USA and Eastern Europe
• Endemic in central river valleys of midwestern and south-central USA
• Affects cavers, bird handlers, cleaning up after birds/bats

Aetiology

• Lesions are calcified fibrinous granulomas with areas of caseous necrosis
• Initial pulmonary infection can spread systemically with extrapulmonary manifestations

Risk of disseminated infection

• AIDS with a CD4 count of less than 150 cells
• Use of corticosteroids
• Haematologic malignancy
• Solid organ transplantation
• Tumour necrosis factor antagonists (eg, etanercept, infliximab)

Clinical

• Most exposures to infection are asymptomatic
• Clinical infections in the immunocompromised
• Acute exposure after an incubation period of 2 to 3 weeks
• Erythema nodosum, fever, malaise and BHL on CXR
• Chronic infection may be seen mainly in male smokers often with COPD
• Fibrosing mediastinitis which has been quoted as causing SVC obstruction
• Histoplasmosis is a rare cause of Adrenal failure
• Disseminated infection ? pancytopenia, hepatomegaly, lymphadenopathy

Investigations

• CXR/CT - Bihilar lymphadenopathy, fibrosis and cyst formation and lung destruction. BHL usually resolves. Nodules of pulmonary calcification may be seen.
• Cortisol and Short Synacthen may show hypoadrenalism
• Blood cultures in disseminated disease
• Positive serology (False-positive tests lymphoma, tuberculosis, or sarcoidosis)
• Anti-M and Anti-G glycoprotein antibodies
• Serum and urine antigen detection

Management

• Itraconazole or amphotericin B may be needed
• Depends on the severity of the infection
• Mild disease resolves spontaneously