Blastomycosis is a systemic mycosis, principally found in North America but also reported in the river valleys of Africa, India, and the Middle East. Sporadic cases and a small number of epidemics suggest this mycosis is endemic to the Mississippi and St. Lawrence River valley basins. Blastomyces dermatitidis may be isolated from soil rich in decaying organic matter and has been associated with the woodland areas along waterways. Sporadic cases are most closely associated with outdoor occupations, but analysis of epidemics does not demonstrate differences in sex, age, race, or occupation (1,4,5).

Blastomyces dermatitidis almost always enters the body through the lungs although direct inoculation of the skin is possible. Approximately 30 to 45 days after exposure half of the patients infected will develop the myalgias, arthralgia, chills, fevers, and dry cough associated with the acute pulmonary phase. From the lung the mycosis may spread hemotogenously to any organ of the body with preference for skin (40% to 89%), the prostate (10% to 30%) and the bones and joints (10% to 30%) (4,5).

Chronic pulmonary disease may manifest with a productive cough or hemoptysis, weight loss, and pleuritic chest pain. Chest x-rays may demonstrate lobar pneumonis, cavitation, mass lesions, fibronodular changes, or miliary patterns. Large pleural effusions are rare (4,5).

Disseminated skin lesions occur in three forms, and a single patient may have all manifestations. The more common lesion is a gray to violet verruci-form plaque, with central scarring and hypopigmentation possible. An exudate may reveal diagnostic yeast. The second form of the skin lesion begins as a pustule and spreads as a superficial ulcer characterized by raised borders and central granulated tissue that bleeds easily with minor trauma. Subcutaneous nodules may appear that represent microabscesses and may also yield diagnostic yeast. Skin disease that results from direct inoculation demonstrates only regional adenitis (2,4,5).

While any bone may become infected, the long bones, vertebrae, and ribs are the most common sites involved. Bony lesions are well-circumscribed osteolytic lesions with contiguous soft tissue spread or draining sinus tracts. Vertebral involvement may manifest as a paravertebral abscess mimicking tuberculosis (2,4,5).

Blastomycosis of the genitourinary tract generally involves the prostate and epididymis, resulting in symptoms of prostatitis and pyuria. Diagnostic yeast may often be recovered from the urine after prostate massage. Treatments for blastomycosis may not effectively penetrate the prostate, which can serve as a nidus for reoccurrence (2,4,5).

Blastomycosis has been reported in the liver, spleen, gastrointestinal tract, thyroid gland, pericardium, and adrenal glands. The central nervous system is seldom directly involved unless the host is immunocompromised, such as in HIV infection.

Identification of the distinctive yeast phase from tissue using KOH prep or silver stain is diagnostic of blastomycosis. DNA probe assay can provide specific and rapid identification of cultures (6).

An immunocompetent host with mild or moderate disease can be treated with ketoconazole or itraconazole. Immune impaired hosts and those with severe disease should be treated with amphotericin B (5).

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