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A 31-year-old man from northern Ontario had acute swelling, purpura and pain in his left lateral forefoot region, which increased progressively over 10 weeks until he became bedridden. A clinical diagnosis of gout was made, but the pain did not improve with NSAIDs. One month later, a small pustule developed that progressed to an ulcer with purulent drainage. On presentation 1 month later, his left foot was swollen, and the lateral forefoot was exquisitely tender to palpation. A 2-cm ulcer, which probed to bone, was present on the lateral aspect of the foot (Fig. 1). The patient was afebrile, and findings on general medical and pulmonary examinations were unremarkable. A plain radiograph of the foot revealed dystrophic calcification in the soft tissues, with osteopenia and periosteal reaction along the fifth metatarsal bone consistent with active osteomyelitis (Fig. 2). The chest radiograph appeared normal.
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Intravenous therapy with ciprofloxacin and clindamycin was started empirically. Staphylococcus aureus and Streptococcus agalactiae (group B streptococcus) were recovered from the deep wound swab. The patient's condition did not improve after a week of parenteral antibacterial therapy. Surgical débridement revealed a pocket of grossly necrotic tissue that had replaced part of the fifth metatarsal. Histologic examination revealed broad-based budding yeast consistent with Blastomyces dermatitidis (Fig. 3). The antibiotic therapy was replaced by treatment with amphotericin B (40 mg intravenously once daily) for 1 week followed by itraconazole (400 mg orally once daily) to complete a 12-month course. The patient had prompt relief of pain, with healing of the wound and radiographic evidence of bone reconstitution occurring within 6 months.
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Blastomycosis is an uncommon granulomatous systemic fungal infection caused by the thermally dimorphic fungus B. dermatitidis.1 Areas in North America in which this fungus is endemic include the Ohio and Mississippi River basins and the regions that border the Great Lakes.1 The annual incidence of blastomycosis is greater in the district of Kenora, Ont., than in all of Manitoba (7.1 v. 0.6 cases per 100 000 people).2
B. dermatitidis exists in a mycelial form in the soil, but when disturbed, the released conidia are inhaled and converted to thick-walled budding yeasts that cause respiratory infection and hematogenous dissemination producing extrapulmonary disease.2 The median incubation period is 30–45 days. Pulmonary disease may be acute or chronic and can mimic infection from other fungi, malignant disease or infection from pyogenic bacteria or Mycobacterium tuberculosis. Extrapulmonary sites most commonly involve the skin, bone and genitourinary system1 and occur most likely at the time of the primary infection, with potential for later relapse.
Patients with blastomycosis osteomyelitis most frequently present with pain and swelling of the affected area, often accompanied with an overlying skin abscess.1 Most cases respond to treatment with antifungal drugs (amphotericin B and agents from the azole class), but some may also require surgical débridement.3 Blastomycosis was suspected in our patient because of his history of residence in an area where the fungus is endemic, an unusual protracted course and an atypical location of the foot lesion. Furthermore, he did not have evidence of the more common causes of ulcers on the lower extremities, such as diabetic neuropathy (ulcer on weight-bearing surface, or areas of bony or shoe pressure), venous stasis disease (leg ulcer and venous stasis changes), gout (ulcer adjacent to joints and tophaceous debris) or lymphedema (ulcer with serous drainage and diffuse limb swelling).
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