Pseudo-Lichenoid Onychodystrophy in AL Amyloidosis: A Case Report

Background

Systemic AL amyloidosis may involve the skin and mucosa, but nail involvement is uncommon and can mimic inflammatory or infectious nail disorders. This case describes diffuse pseudo-lichenoid onychodystrophy associated with systemic AL amyloidosis and highlights the diagnostic role of nail histopathology. Presentation of Case: A 64-year-old woman with newly diagnosed systemic AL amyloidosis and cardiac and renal involvement was referred for onychodystrophy affecting all 20 nails for more than four years. Examination showed longitudinal ridging, onychorrhexis, longitudinal melanonychia, trachyonychia, koilonychia, pachyonychia, and toenail xanthopachyonychia, together with sausage-like swelling of the fingers. Onychoscopy demonstrated splinter haemorrhages, and periungual dermoscopy showed thickened cuticles, reduced capillary density, dilated capillaries, fern-leaf branching, and a pseudo-Hutchinson sign. A longitudinal lateral nail biopsy demonstrated dermal amyloid deposits confirmed by Congo red staining and apple-green birefringence under polarised light, with a subepidermal lymphohistiocytic infiltrate. Mycological examination also identified Trichophyton rubrum onychomycosis.