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For further information, see CMDT Part 36-03: Histoplasmosis

Key Features

Essentials of Diagnosis

  • Exposure to bird and bat droppings; common along river valleys (especially the Ohio River and the Mississippi River valleys)

  • Most patients are asymptomatic; respiratory illness is the most common clinical problem

  • Disseminated disease is common in AIDS or other immunosuppressed states; poor prognosis

  • Blood and bone marrow cultures and urine polysaccharide antigen are useful in diagnosis of disseminated disease

General Considerations

  • Acute histoplasmosis frequently occurs in epidemics, often when soil containing infected bird or bat droppings is disturbed

  • Infection presumably occurs by inhalation of conidia

  • These convert into small budding cells that are engulfed by phagocytes in the lungs

  • The organism then proliferates and undergoes lymphohematogenous spread to other organs

  • Progressive disseminated histoplasmosis is commonly seen in patients with underlying HIV infection (with CD4 cell counts usually < 100 cells/mcL) or other conditions of impaired cellular immunity

Demographics

  • Endemic areas

    • Central and eastern United States (especially Ohio River and Mississippi River valleys)

    • Eastern Canada

    • Mexico

    • Central America

    • South America

    • Africa

    • Southeast Asia

  • Cases are increasingly being recognized outside of endemic areas

  • Chronic progressive pulmonary histoplasmosis occurs in older patients with chronic obstructive pulmonary disease

Clinical Findings

Symptoms and Signs

  • Most cases are asymptomatic with no pulmonary symptoms or signs even in those who later have calcifications on chest radiograph

  • Mild symptomatic illness: influenza-like illness, often lasting 1–4 days

  • More severe illness: presents as atypical pneumonia, with fever, cough, and mild central chest pain for 5–15 days

  • Physical examination is usually normal

  • Acute pulmonary histoplasmosis: clinical manifestations can vary from a mild influenza-like illness to life-threatening pneumonia

  • Progressive histoplasmosis

    • Fever, weight loss, prostration

    • Dyspnea, cough

    • Ulcers of the mucous membranes of the oropharynx

    • Liver and spleen are nearly always enlarged

    • All organs of the body are involved, particularly the adrenal glands, though this infrequently results in adrenal insufficiency

    • Gastrointestinal involvement may mimic inflammatory bowel disease

    • Central nervous system (CNS) invasion occurs in 5–10% of individuals with disseminated disease

  • Disseminated histoplasmosis occurs mainly in immunocompromised patients

    • Fever and multiple organ system involvement

    • Presentation may be fulminant, simulating septic shock

Differential Diagnosis

  • Influenza

  • Atypical pneumonia

  • Tuberculosis

  • Coccidioidomycosis

  • Sarcoidosis

  • Blastomycosis

  • Pneumoconiosis

  • Pneumocystis jirovecii pneumonia

  • Lymphoma (including lymphocytic interstitial pneumonia)

Diagnosis

Laboratory Tests

  • Elevations of serum lactate dehydrogenase (marked) and ferritin are common

  • Serum aspartate aminotransferase levels are mildly elevated

  • Anemia of chronic disease occurs in chronic pulmonary histoplasmosis

  • Sputum culture is rarely positive except in chronic pulmonary histoplasmosis

  • Antigen testing of bronchoalveolar lavage fluid may be helpful in acute disease

  • Blood or bone marrow cultures are positive in > 80% of disseminated disease in immunocompromised individuals

  • Bone marrow involvement with pancytopenia may be prominent in ...

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