Blastomycosis

SOURCE

Source: Carver PL. Invasive fungal infections. In: DiPiro JT, Talbert RL, Yee GC, Matzke GR, Wells BG, Posey LM. Pharmacotherapy: A Pathophysiologic Approach. 10th ed. New York, NY: McGraw-Hill; 2017. http://accesspharmacy.mhmedical.com/content.aspx?bookid=1861&sectionid=146073167. Accessed March 14, 2017.

DEFINITION

• Systemic fungal infection.

ETIOLOGY

• Systemic fungal infection caused by Blastomyces dermatitidis

PATHOPHYSIOLOGY

• Pulmonary infection probably occurs by inhalation of conidia, which convert to yeast form in lung.

• Inflammatory response, followed by cell-mediated immunity and formation of noncaseating granulomas.

EPIDEMIOLOGY

• B. dermatitidis considered to be soil inhabitant, though attempts to isolate it in nature have frequently been unsuccessful.

• Has been found in soil containing decayed vegetation, decomposed wood, and pigeon manure.

• Found in southeastern, south central, and midwestern United States as well as Canadian provinces that border the Great Lakes.

RISK FACTORS

• No sex, age, or occupational predilection.

• Review of sporadic cases suggests that people with outdoor occupations that expose them to soil at highest risk.

CLINICAL PRESENTATION

SIGNS AND SYMPTOMS

• Colonization does not occur.

• Can disseminate to virtually every other body organ, including skin, bones, and joints, or the genitourinary tract, without evidence of pulmonary disease.

• Acute pulmonary blastomycosis.

  • Generally asymptomatic or self-limited disease.

  • Characterized by fever, shaking chills, and productive, purulent cough, with or without hemoptysis in immunocompetent individuals.

  • Difficult to differentiate from other respiratory infections based on symptoms.

• Sporadic pulmonary blastomycosis.

  • More chronic or subacute disease.

  • Characterized by low-grade fever, night sweats, weight loss, and productive cough resembling that of TB rather than bacterial pneumonia.

• Chronic pulmonary blastomycosis.

  • Characterized by fever, malaise, weight loss, night sweats, chest pain, and productive cough.

  • Evidence of disseminated disease can appear 1–3 years after resolution of primary pneumonia.

    • 40% of patients with disseminated disease do not have reactivation of pulmonary disease.

    • Most common sites include skin and bony skeleton.

      • Male urogenital tract may also be involved.

DIAGNOSIS

MEANS OF CONFIRMATION AND DIAGNOSIS

• Direct microscopic visualization of large, multinucleated yeast with single, broad-based buds in sputum or other respiratory specimens, following digestion of cells and debris with 10% potassium hydroxide.

• No reliable skin test available.

LABORATORY TESTS

• Culture secretions: up to 30 days required to isolate and identify small inoculum.

• Complete blood count (CBC): leukocytosis and anemia may be present.

IMAGING

• Chest radiograph.

• CT scan.

DIAGNOSTIC PROCEDURES

• Histopathologic examination of tissue biopsies and culture of secretions.

DIFFERENTIAL DIAGNOSIS

• Tuberculosis

• Bacterial pneumonia.

• Malignancy.

• Other fungal infection.