P0656 - That 'Blast'ed Knee Pain

Introduction
Blastomycosis, formerly Chicago Disease, is an endemic fungus to the Ohio and Mississippi River Valleys and Great Lakes region. Although Illinois has the second highest rate of hospitalizations due to blastomycosis, its relative infrequency continues to make infections due to this pathogen a diagnostic challenge.1 Commonly a pulmonary pathogen; here, we present a case of blastomycosis with osteomyelitis and penile lesions.

Case Presentation:
A 15-year-old male with mild intermittent asthma presented to his pediatrician with 6 weeks of atraumatic, waxing and waning, right knee pain. Symptoms were exacerbated with activity and associated with decreased range of motion. He recalled self-resolving penile lesions 2 months prior to presentation and a febrile illness ~3 weeks prior to pain onset. He denied sexual activity and reported testing for STIs was negative.

Evaluation:
MRI demonstrated right medial femur condyle lesion, concerning for infection versus tumor. The patient was admitted for open biopsy and curettage. Intraoperatively, gross purulence was noted upon opening the cortex. Bone and tissue cultures were sent for anaerobic, aerobic, and acid-fast bacilli evaluation. The patient was started on IV clindamycin for empiric osteomyelitis coverage.

Hospital Course:
The patient remained afebrile. CBC revealed a mild leukocytosis (WBC 11) with neutrophil predominance (85.7%) and CRP was within normal limits. Initial microbiology was unremarkable, with no growth isolated on peripheral blood cultures or MRSA isolated from intraoperative samples.

Intraoperative tissue culture and bone biopsy results revealed acute, granulomatous inflammation with Blastomyces dermatitidis growth. Antimicrobial therapy was transitioned to itraconazole.

Discussion:
Inhalation of airborne conidia introduces blastomyces to the host’s alveoli. Lymphohematogenous spread then causes systemic disease. After pulmonary and cutaneous infections, osseous and genitourinary manifestations are the next most common sites of blastomycosis.2

The subacute osteomyelitis of blastomycosis develops indolently, and often without associated systemic symptoms.3 Localized mass symptoms and initial imaging can be suspicious for tumor, delaying diagnosis.4 In pediatric patients, trauma is the most prevalent mode of infection as compared to adults, more commonly infected through prior surgeries. Like this patient, lower limbs and knees are commonly affected in pediatrics.

Fifteen to 30% of blastomycosis cases involve the genitourinary system.5 Often presenting with urethritis, cystitis, epididymitis, or prostatitis symptoms, blastomyces can also infect the penile skin.6 While our patient’s penile lesions were not sampled, they may represent the first manifestation of his systemic fungal infection.

This case represents an uncommon presentation of a common pathogen, emphasizing the importance of familiarity with uncommon presentations of endemic fungal infections.