Relapse of Sporotrichosis Presenting as Insidious Fungal Arthritis of the Knee After Treated Mucocutaneous Disease: A Case Report With a Protracted Course and Unsatisfactory Therapeutic Response

Sporotrichosis is an infection caused by fungi of the Sporothrix complex, usually acquired through cutaneous inoculation. While cutaneous forms are common, osteoarticular presentations are rare and challenging, especially in immunocompetent patients or those with chronic comorbidities. We report a case of fungal arthritis diagnosed late, probably representing recurrence of a previously treated infection. A 58-year-old woman with type 2 diabetes mellitus and chronic kidney disease (stage II–IIIa) was treated in 2022 for mucocutaneous sporotrichosis of the right thumb with oral itraconazole 400 mg/day for 8 months, achieving clinical remission. She remained asymptomatic until January 2024, when she was admitted for elective left knee arthroplasty. Intraoperatively, purulent discharge and material suggestive of fungal infection were observed, the procedure was aborted, and antibiotic-loaded cement was placed. Direct exam revealed structures compatible with Sporothrix spp., and bone culture confirmed infection by the Sporothrix schenckii complex, establishing the diagnosis of osteoarticular sporotrichosis. A new course of oral itraconazole 400 mg/day was started, later combined with liposomal amphotericin B (April 2025) due to lack of clinical improvement. Antifungal therapy was initially given daily, but after deterioration of renal function (14/05/2025), an intermittent regimen (three times per week) was adopted, with day-hospital follow-up. Despite more than one year of antifungal treatment, the patient continues to experience pain, swelling, and radiologic findings consistent with chronic osteomyelitis, showing only a partial clinical response and significant functional limitation. This case represents an unusual recurrence of sporotrichosis with insidious monoarticular involvement, with diagnosis made only intraoperatively. Persistent infection despite prolonged and adequate antifungal regimens underscores the therapeutic challenges of osteoarticular sporotrichosis, particularly in patients with chronic comorbidities that limit optimal therapy. Recurrence of sporotrichosis, even after successful treatment of mucocutaneous forms, should be considered in patients with subacute osteoarticular manifestations. This case reinforces the importance of long-term surveillance, microbiological assessment during surgery, and individualized therapeutic strategies in atypical presentations of this mycosis.