Primary Cutaneous Nodular Amyloidosis Presenting As Violaceous Patches on Bilateral Plantar Feet

Primary localized cutaneous amyloidosis (PLCA) is characterized by amyloid deposition limited to the skin and is subdivided into macular, lichenoid, and nodular variants. Primary cutaneous nodular amyloidosis (PCNA) is the rarest subtype and typically presents as waxy, firm nodules or plaques composed of immunoglobulin light chain-derived (AL-type) amyloid. Plantar involvement is exceedingly uncommon. We report the case of a 64-year-old Hispanic man found incidentally to have bilateral, well-demarcated, flat violaceous patches on the plantar surfaces of both feet. The lesions were asymptomatic, non-nodular, and lacked overlying epidermal change. Histopathologic examination revealed amorphous eosinophilic deposits within the dermis, which stained positive with Congo red and exhibited apple-green birefringence under polarized light, confirming amyloid deposition. The patient was diagnosed with PCNA, presenting with atypical patch-like morphology, and managed conservatively with close clinical surveillance. This case represents an unusual clinical presentation of PCNA, diverging from the classic nodular phenotype and mimicking inflammatory or granulomatous dermatoses. To our knowledge, this is among the first reported cases of plantar PCNA presenting as flat violaceous patches rather than nodules. Given the potential risk of progression to systemic amyloidosis, accurate diagnosis and ongoing monitoring remain essential. Awareness of this expanded clinical spectrum underscores the importance of histopathologic evaluation in atypical acral dermatoses and may help prevent misdiagnosis or delayed recognition of this rare entity.