Histoplasmosis - Pulmonary
Classical histoplasmosis is endemic to the Ohio/Mississippi River Valley and South and Central America. Bird and bat excrement enhance the growth of the organism in the soil. Initially, microconidia are inhaled into the lungs where they transform into yeast forms.
There are 3 forms of the disease: pulmonary (acute and chronic), disseminated (acute and chronic), and primary cutaneous histoplasmosis. The clinical presentation depends upon the patient's immune status, the intensity of exposure, and previous immunity. A low-intensity exposure will result in asymptomatic infection 90% of the time. A heavy exposure results in symptomatic disease a majority of the time.
In acute pulmonary histoplasmosis, the patient presents with cough, chest pain, fever, and occasionally a rash caused by immune complexes (erythema multiforme, toxic erythema, or erythema nodosum). Chronic pulmonary histoplasmosis resembles pulmonary tuberculosis and is not usually associated with skin findings. Pericarditis may develop (in 5% of cases).
Progressive pulmonary histoplasmosis results in 1:100,000 cases per year following acute infection or activation of prior disease. The clinical presentation includes pulmonary symptoms consistent with apical lung cavities and fibrosis resulting from an immune response. Symptoms resemble granulomatous disease. In 50% of cases, a chronic infection and fibrosis results. The immunosuppressed and those with pre-existing lung disease are at greatest risk.
In patients with acute disseminated histoplasmosis, the fungus spreads to other organs such as the liver, spleen, and bone marrow. This form commonly is seen in immunocompromised patients. Skin rash is more common in the disseminated form. Severe weight loss, fever, anemia, and hepatosplenomegaly can result.
Chronic disseminated histoplasmosis commonly appears months after a patient has left an endemic area. Patients may present with oral or pharyngeal ulcerations or with adrenal insufficiency after adrenal infiltration. Disseminated histoplasmosis may be complicated by central nervous system infection in 5–10% of cases and can manifest as meningitis, endocarditis, or pericarditis.
Primary cutaneous histoplasmosis is rare and occurs after trauma to the skin with an infected instrument. This may present as a nodule or indurated ulcer with associated lymphadenopathy.
In general, people at higher risk of exposure to infected soils include spelunkers, construction workers, and agricultural workers. Risk factors for systemic histoplasmosis include many immunosuppressed states. Disseminated histoplasmosis is considered as an AIDS-defining illness. AIDS patients with histoplasmosis usually present with weight loss and fever.
B39.9 – Histoplasmosis, unspecified
12962009 – Histoplasmosis
The differential diagnosis of pulmonary histoplasmosis is the same list of diseases that can induce either erythema multiforme or erythema nodosum. These include the following infections: