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Case Reports

Abstract

We report a diagnostically challenging case of a 27-year-old male with a complex medical history, including CTLA-4 haploinsufficiency, autoimmune enteropathy, gastrointestinal graft-versus-host disease, hypogammaglobulinemia, and prior gastric adenocarcinoma. He presented with fever, malaise, myalgia/arthralgia, right knee tenderness, and respiratory failure. Physical examination revealed multiple tender subcutaneous nodules. A punch biopsy of the right knee showed a mixed perivascular inflammatory infiltrate in the dermis with extension into subcutaneous fat, involving both lobules and septae. Key findings included fat necrosis, fibrin deposition, and necroinflammatory debris. Numerous cysts and trophozoite-like organisms were identified in the adipose tissue and highlighted by GMS and PAS-O stains.  A protozoal infection was suspected, with Acanthamoeba and Balamuthia mandrillaris in the differential. Molecular testing confirmed Balamuthia mandrillaris, a free-living amoeba rarely encountered in cutaneous infections. Systemic dissemination, including pulmonary involvement, was subsequently identified.  Further history revealed recent exposure to shallow, untreated water-an environmental risk factor for Balamuthia infection.  While Balamuthia and Acanthamoeba are primarily associated with granulomatous amebic encephalitis and Naegleria fowleri with necrotizing encephalitis, cutaneous manifestations are exceedingly rare and often the first clue to the diagnosis. Early skin biopsy and histopathologic recognition are critical before CNS involvement.  Despite aggressive therapy, the patient died after three months-reflecting the nearly 100% fatality rate of disseminated Balamuthia infection. This case emphasizes how dermatopathology can enable early detection and histologic distinction of rare amoebic pathogens.