Histoplasmosis

SOURCE

Source: Carver PL. Invasive fungal infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM, eds. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146073167. Accessed February 23, 2017.

DEFINITION

• Systemic fungal infection.

ETIOLOGY

• Inhalation of dust-borne Histoplasma capsulatum

• Acute histoplasmosis may occur in epidemics when soil disturbed.

PATHOPHYSIOLOGY

• Aerosolized H. capsulatum is inhaled and settles in lungs.

• Tissue granulomas form over 2–4 months.

  • Foci become encapsulated and calcified over several years.

• Low-inoculum exposure results in benign disease course.

• Higher-inoculum exposure results in acute, self-limited illness.

  • Fever.

  • Chills.

  • Headache.

  • Myalgia.

  • Nonproductive cough.

• Chronic pulmonary histoplasmosis.

  • Progressive disease over period of years.

    • Cavitation.

    • Bronchopleural fistulas.

    • Involvement of both lungs.

    • Pulmonary insufficiency.

    • Death.

• Immunocompromised hosts.

  • Progressive, disseminated histoplasmosis.

• Acute disseminated histoplasmosis.

  • Infants and young children: fatal in 1–2 months if untreated.

  • Adults: untreated patients ill for 10–20 years, with long asymptomatic periods.

• Histoplasmosis in HIV-infected patients.

  • Progressive disseminated histoplasmosis (PDH) serves as the first manifestation of AIDS in 50% of HIV-infected patients.

  • Symptoms include fever, weight loss, chills, night sweats, enlargement of spleen, liver, or lymph nodes, and anemia.

EPIDEMIOLOGY

• Localized along Ohio and Mississippi River valleys in United States.

• Found in nitrogen-enriched soils, particularly those contaminated by avian or bat guano.

RISK FACTORS

• Immunosuppression (eg, AIDS)

CLINICAL PRESENTATION

• Immunocompromised hosts.

  • Adults with AIDS present with acute form of disseminated disease that resembles syndrome seen in infants and children.

SIGNS AND SYMPTOMS

• Chronic pulmonary histoplasmosis.

  • Chronic pulmonary symptoms.

  • Apical lung lesions.

• Acute disseminated histoplasmosis.

  • Infants and young children.

    • Unrelenting fever.

    • Anemia.

    • Leukopenia or thrombocytopenia.

    • Enlargement of liver, spleen, and visceral lymph nodes.

    • Gastrointestinal (GI) symptoms: nausea, vomiting, diarrhea.

  • Adults.

    • Long asymptomatic periods interrupted by.

      • Weight loss.

      • Weakness.

      • Fatigue.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Serologic testing.

  • Complement fixation.

  • Immunodiffusion.

  • Enzyme immunoassay (EIA)

LABORATORY TESTS

• Culture.

  • Identification of mycelial isolates from clinical cultures can be made by conversion of mycelium to yeast form (requires 3–6 weeks) or by more rapid (2 hours) and 100%-sensitive DNA probe that recognizes ribosomal DNA.

IMAGING

• Chest radiograph.

DIAGNOSTIC PROCEDURES

• Bone marrow biopsy and culture is the best method to establish diagnosis in AIDS patients with progressive disseminated histoplasmosis.

DIFFERENTIAL DIAGNOSIS

• Influenza

• Atypical pneumonia.

• Tuberculosis

• Lymphoma.

• Other fungal infection.

DESIRED OUTCOMES

• Resolution of clinical abnormalities.

• Prevention of relapse.

• Eradication of infection.

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