Foot Ulcers
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.
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.
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).
References:
Chapman
SW. Blastomyces dermatitidis. In: Mandell CL, Bennell JE, Dolin R,
editors. Principles and practice of infectious diseases. 6th ed.
Philadelphia: Churchill Livingston; 2005. p. 3027-40.
Crampton TL,
Light RB, Berg GM, et al. Epidemiology and clinical spectrum of
blastomycosis diagnosed at Manitoba hospitals. Clin Infect Dis 2002; 34:
1310-6.[CrossRef][Medline]
Chapman SW, Bradsher RW Jr, Campbell GD
Jr, et al. Practice guidelines for the management of patients with
blastomycosis. Infectious Diseases Society of America. Clin Infect Dis
2000;30:679-83.[CrossRef][Medline]
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