Abstract
Systemic amyloid light-chain (AL) amyloidosis is a multisystem disorder caused by extracellular deposition of monoclonal immunoglobulin light chains. Cutaneous manifestations are diverse, but nail involvement is uncommon and may lead to diagnostic delay. We report the case of a 53-year-old man presenting with progressive dystrophy affecting all 20 nails for 18 months. Clinical examination revealed marked nail plate atrophy and onychorrhexis. Dermoscopy demonstrated nail plate atrophy, subungual hyperkeratosis, and splinter hemorrhages. A longitudinal lateral nail-bed biopsy revealed abundant amorphous eosinophilic deposits in the papillary dermis on hematoxylin and eosin staining. Congo red staining confirmed amyloid deposition. Subsequent systemic evaluation revealed markedly elevated free lambda light chains and bone marrow plasmacytosis, establishing the diagnosis of systemic AL amyloidosis associated with multiple myeloma. This case highlights that unexplained progressive pan-ungual dystrophy may represent an early manifestation of systemic amyloidosis. Early recognition and nail-unit biopsy can facilitate prompt diagnosis of this potentially fatal systemic disease.