Abstract
Primary systemic amyloidosis rarely has been reported to involve the sacrum. We describe a case of sacral ulcers which posed a diagnostic challenge until skin biopsy confirmed amyloidosis. A 56-year-old man with no prior medical history presented with fatigue, back pain, and painful ulcers involving the sacrum and buttocks. Upon admission, he was found to be in renal failure and had diffuse lytic bone lesions. His sacral and gluteal skin had well-demarcated ulcers within erythematous to hyperpigmented patches and thin plaques. He had no other areas of skin involvement. Infectious workup including HSV, mpox, syphilis, HIV, and tissue cultures for bacteria, fungi, and acid-fast bacilli were negative. A punch biopsy specimen from an ulcer edge revealed extensive superficial and deep dermal and perivascular amyloid deposition, which was highlighted with Congo red staining and demonstrated focal apple green birefringence. Serum protein electrophoresis demonstrated a monoclonal lambda band. Serum free lambda light chains were elevated to 19,603 mg/L with a free lambda/kappa ratio of 598 (multiple myeloma diagnostic criteria include one free light chain ≥10 mg/dL and free light chain ratio ≥100). Sacral cutaneous amyloidosis is rare, and prior cases have been described as hyperkeratotic brown patches and plaques. A bullous variant of cutaneous amyloidosis has been well described but differs in clinical presentation from our case. To our knowledge, prior cases of cutaneous amyloidosis presenting as sacral ulcerations have not been reported. This entity should be considered when patients with systemic light chain disease or multiple myeloma develop sacral ulcers.