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An infectious disease caused by the fungus Blastomyces dermatitidis, primarily involving the lungs and occasionally spreading hematogenously, characteristically to the skin.
Etiology, Incidence, and Pathology
The environmental source is not established, but association with beaver huts has been suggested in a recent outbreak. Most reported cases are from the USA, chiefly in the southeastern states and the Mississippi River valley, and in men aged 20 to 40. A sufficient number of cases from widely scattered sites in Africa now precludes geographic limitation of the disease name. Disease occurs prominently in dogs and may be a harbinger of that in humans; it has been reported to follow dog bites. The disease is rare in patients with AIDS. Histopathologic characteristics include a combination of suppurative and granulomatous necrosis with polymorphonuclear, mononuclear, fibrous, and giant cells.
Symptoms and Signs
Pulmonary form: Primary pulmonary blastomycosis frequently forms patches of bronchopneumonia that appear, on chest film, to fan out from the hilum like a neoplastic growth. Onset is usually insidious. A dry hacking or productive cough, chest pain, fever, chills, drenching sweats, and dyspnea are initial symptoms. Pleural effusion occurs in lesser 10% of patients.
Disseminated form: Sites of hematogenous spread include skin, prostate, epididymis, testis, bone, subcutaneous tissue, and rarely, oral or nasal mucosa. The vertebrae, tibia, and femur are more commonly involved than other bones; swelling, heat, and tenderness are present over the lesion. Genital tract lesions are characterized by painful swelling, typically of the epididymis, or deep perineal discomfort from prostatitis.
Skin lesions begin as papules or papulopustules on exposed surfaces briefly and spread slowly. Painless miliary abscesses, varying from pinpoint to 1 mm in diameter, develop on the advancing borders. Irregular, wartlike papillae form on the surfaces. As the lesions enlarge, the center heals with a typical atrophic scar. A fully developed individual lesion appears as an elevated verrucous patch measuring > 2 cm with an abruptly sloping, purplish-red, abscess-studded border. Ulceration may occur if bacteria are present.
Diagnosis
Diagnosis is by culture and identification of B. dermatitidis but is almost as certain if thick-walled budding yeasts, about 15 mu in diameter and without a capsule, are seen on direct examination of pus, sputum, or exudate. The diagnosis can also be made histopathologically if forms suggestive of B. dermatitidis are seen in tissues stained with Gomori's methenamine-silver, periodic acid-Schiff, or Gridley's stain; the organism can be distinguished from C. neoformans, which may stain with Mayer's mucicarmine, whereas B. dermatitidis does not. Skin and serologic tests are of no value.
Pulmonary disease must be distinguished from TB, other fungus infections, and bronchogenic carcinoma. Skin lesions resemble sporotrichosis, TB, iodism, or especially, basal cell carcinoma. Genital involvement mimics TB. The early criteria for distinguishing progressive from nonprogressive pulmonary disease are not established.
Prognosis and Treatment
In most untreated patients, the disease is slowly and fatally progressive. Amphotericin B (see General Therapeutic Principles, above) is effective. Improvement begins within a week, with rapid disappearance of microorganisms from sites of specimens previously positive.
Hydroxystilbamidine isethionate is rarely used today. Ketoconazole (see General Therapeutic Principles, above) 400 to 800 mg orally given as a single daily dose is effective in about 75% of patients. Greater efficacy, but also toxicity, is associated with larger doses. Arguments for use of ketoconazole in preference to amphotericin B rest on the oral route of administration and milder side effects.
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