Pseudo-Lichenoid Onychodystrophy in AL Amyloidosis: A Case Report

Abstract

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. Discussion: The presentation closely resembled nail lichen planus, illustrating the non-specific clinical appearance of nail amyloidosis and the potential contribution of concomitant fungal infection to nail dystrophy. Histopathological examination was decisive for diagnosis. Conclusion: In patients with systemic AL amyloidosis and chronic atypical twenty-nail dystrophy, nail biopsy may help distinguish amyloid-related changes from clinically similar nail disorders and clarify the cause of persistent onychodystrophy.