Sporotrichosis is a fungal infection caused by species of the genus Sporothrix , with S. brasiliensis being the most prevalent in Brazil due to zoonotic transmission. Although it is primarily recognized for its cutaneous manifestations, especially the lymphocutaneous form, its simultaneous occurrence with erythema nodosum—a hypersensitivity reaction characterized by painful, erythematous nodules with a self-limited course—is considered relatively rare. The frequency of this association in clinical settings is not extensively documented; however, case reports and studies provide important insights into this coexistence. The present study describes a clinical case that illustrates this rare concomitance. A 10-year-old male patient presented with a pruritic ulcerative lesion with purulent secretion in the lower left quadrant of the right abdomen. Concomitantly, diffuse erythematous and violaceous lesions developed on the upper and lower limbs, which were indurated and thickened. The condition was accompanied by headache, fever, and loss of appetite. The patient’s mother had ulcerative lesions on the trunk, and at the time, five cats raised by the family were diagnosed with sporotrichosis. On physical examination, a single abdominal lesion on the right side was observed, with irregular borders and no active secretion; the limb lesions remained diffuse, indurated, and thickened, with no lymphadenopathy. Treatment with itraconazole 100 mg was initiated. Direct mycological examination was negative, but culture was positive for Sporothrix , with significant clinical improvement. The concomitant occurrence of erythema nodosum and sporotrichosis is an uncommon finding in the global literature, with most reports originating from Brazil. Although it may be considered an incidental finding, authors such as Galhardo and Gutierrez (2002) have already documented this association in similar cases, reporting three occurrences, particularly in endemic areas of sporotrichosis, suggesting that it is not coincidental. The fungal infection triggers an immune response which, influenced by host immunity, fungal inoculum, and strain characteristics, may result not only in typical ulcerated lesions but also in a hypersensitivity reaction manifesting as erythema nodosum, highlighting the complex interaction between the pathogen and the host immune response.
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