Primary Systemic Amyloidosis Characterized by Multiple Keratinous Cysts: A Case Report

Primary systemic amyloidosis (PSA) is a systemic disease caused by amyloid deposition in various tissues and organs. In the early stages of the disease, approximately 40% of patients have skin damage, which may be the only clinical manifestation. This report described the case of a 67-year-old male with PSA who presented with characteristic cutaneous manifestations. Physical examination showed seborrheic keratotic-like plaques around the orbit, purpura and ecchymosis on the neck and dorsum manus, as well as nail dystrophy. An auxiliary examination indicated a 24-h urine protein content of 2.89 g, and serum immunoelectrophoresis showed a monoclonal λ light chain. Echocardiography showed decreased left ventricular diastolic function and mild pulmonary hypertension. The dermoscopic features were multiple comedo-like openings and milia-like cysts. Histopathology showed multiple keratinous cysts in the dermis and eosinophilic, acellular, homogenous material in the dermis that was Congo red-positive. The diagnosis was confirmed through biopsy of skin lesions and kidney.Skin lesions of this case are rare.Skin lesions around the orbit need to arouse the vigilance of dermatologists. PSA should be considered if the patient with multisystemic symptoms.Skin biopsy and Congo red staining were very important for early diagnosis of PSA.