Curious facial plaque diagnosed as nodular primary localised cutaneous amyloidosis

Nodular primary localised cutaneous amyloidosis (NPLCA) is the rarest form of cutaneous amyloidosis, with a predilection for facial and acral skin. We present a 63-year-old Caucasian with a 10-year history of an asymptomatic plaque on his left cheek, starting 2 years after being scratched by a cat in the same area. A biopsy showed nodules of eosinophilic material in the deep dermis and subcutaneous fat, with plasma cells in the dermis. Congo red staining displayed apple-green birefringence within the eosinophilic material. Immunohistochemistry for serum amyloid P was positive within the eosinophilic material and immunohistochemistry showed lambda light chain restriction within the plasma cells, consistent with NPLCA. The causal relationship of the cat scratch to NPLCA in our patient remains unclear. While trauma-induced amyloidosis has been recognised in papular and macular amyloid, few case reports indicate an association with nodular amyloidosis.