Classical histoplasmosis is endemic to the Ohio / Mississippi River Valley, South and Central America, northern South America, Brazil, Argentina, Uruguay, and Paraguay.
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.
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.
In patients with acute disseminated histoplasmosis, the fungus spreads to other organs such as the liver, spleen, and bone marrow. This form is commonly 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.
Immunocompromised patients have a high risk of dissemination, particularly those with human immunodeficiency virus (HIV) or lymphoma. The severity of disease is often influenced by other predisposing factors such as corticosteroid use, diabetes, malignancy, and connective tissue disease.
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-infected 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:
- Pneumonic plague
- Molluscum contagiosum
- Pseudomonas folliculitis
- Guttate psoriasis
- Cutaneous tuberculosis
- Aphthous ulcers
- Herpes simplex virus
- Squamous cell carcinoma