Disease/Syndrome

Histoplasmosis

Category

Infection, Occupational

Acute/Chronic

Subacute

Synonyms

Histoplasma capsulatum infection

Biomedical References

Search PubMed

Comments

INITIAL SYMPTOMS: Flu-like syndrome; dry cough; pleuritic chest pain; 99% are asymptomatic after a light inoculum, and 10-50% are asymptomatic after a heavy inoculum. [ID, p. 2220] 90% of infections are asymptomatic or cause mild flu-like symptoms; [CDC Travel] FINDINGS Infection is common, but chronic disease is rare. The five forms of the disease are asymptomatic, acute respiratory, acute disseminated, chronic disseminated, and chronic pulmonary. Most cases of histoplasmosis are detected as incidental radiographic findings such as enlarged mediastinal or hilar lymph nodes and pulmonary nodules. A high-dose exposure can cause an acute respiratory disease within 2 weeks of exposure. Complications of acute infection include arthralgias, erythema multiforme, erythema nodosum, mediastinal adenitis, pericarditis, and uveitis. Frank arthritis and pleural effusions are "distinctly uncommon." Splenic and liver calcifications are signs of resolved histoplasmosis. In severe cases, acute infection can precipitate respiratory failure. Chronic pulmonary disease resembles pulmonary tuberculosis with cavitation; it is found in patients with pre-existing emphysema. Immunocompromised patients are susceptible to the disseminated forms of histoplasmosis with the following complications: mucosal and skin lesions; hepatosplenomegaly and generalized lymphadenopathy; adrenal insufficiency; endocarditis; and infections of the GI tract, CNS, and bone marrow. GI infections may cause an abdominal mass. Patients with hilar lymphadenopathy may be asymptomatic or have dysphagia, chest pain, cough, and dyspnea. 5-10% of histoplasmosis patients present with a septic-shock syndrome with DIC. [Cohen, p. 329, 968] Histoplasmosis is one of the uncommon causes of nodular lymphangitis; [Am Fam Physician 2001;63:326-32] LABORATORY: Laboratory evidence of dissemination includes anemia, leukopenia, thrombocytopenia, and elevated hepatic transaminases. In acute and subacute pulmonary histoplasmosis, testing for antigens in urine and bronchoalveolar lavage fluid (BALF) makes the diagnosis in about 75% of the cases. The usefulness of serology is limited because the results remain positive for years after initial infection. 10% of residents in endemic areas have low levels of antibodies. False negatives are common in HIV infected patients. BALF should also be cultured and stained (Diff-Quick, Giemsa, and GMS). Antigen detection is a rapid test for diagnosis and monitoring response to treatment, but cross-reactivity in patients with blastomycosis, penicilliosis, and paracoccidioidomycosis. [CCDM, p. 285; Merck Manual, p. 1330; ID, p. 2220-1; Cecil, p. 1977-9; Harrison, p. 753-4; Guerrant, p. 573-575, 921;] DISSEMINATED DISEASE: Over 90% of histoplasmosis cases are subclinical. In an acute primary infection 7-21 days after exposure, the main findings are fever, headache, nonproductive cough, chest pain, rales, patchy infiltrates, and hilar adenopathy. About 6% of patients have acute pericarditis. Most cases of progressive disseminated histoplasmosis occur in immunosuppressed patients. Diarrhea, abdominal pain, and ulcers of GI tract are common; ulcers of the skin, mouth, and throat are also found. In disseminated disease in AIDS patients, skin findings include petechiae, ecchymoses, maculopapular rash, nodules, and pustules. [PPID, p. 2953-7] Findings in disseminated disease include meningitis, brain lesions, coagulopathy, rhabdomyolysis, mediastinitis, and loss of vision with unclear link to H. capsulatum infection. {Merck Manual, p. 1331] AFRICAN HISTOPLASMOSIS: African histoplasmosis is caused by H. capsulatum var. duboisii, which is a larger yeast form up to 15 microns in diameter. The organism is resistant to phagocytosis by macrophages. It causes osteolytic bone lesions and skin ulcers, nodules, and abscesses. [PPID, p. 2958]

Latency/Incubation

7-21 days, usually <15 days; [PPID]

Diagnostic

Tissue stains; Culture; Serology most useful in chronic forms (CF >1:32 is suggestive or 4-fold rise); Antigen detection: In AIDS patients, sensitivity is 95% (urine) and 85% (serum); [ABX Guide]

ICD-9 Code

115

Effective Antimicrobics

Yes

Reference Link

CDC - Histoplasmosis

X-Ray

eMedicine - Histoplasmosis, Thoracic : Article by Fahad M Alhameed, MD, FRCPC

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