Nail dystrophy is a broad term for any structural abnormality of the nail apparatus, encompassing changes in the nail plate (pitting, ridging, splitting, thickening, thinning), nail bed (onycholysis, subungual hyperkeratosis, hemorrhage, color change), and nail matrix (proximal nail plate disturbances, pterygium, anonychia). Etiology spans inflammatory dermatoses, infections, trauma, systemic disease, drug-induced, and congenital/genetic disorders.
Pattern recognition guides diagnosis. Psoriasis causes pitting (deep, irregular), oil drops/salmon patches, subungual hyperkeratosis, and onycholysis. Lichen planus produces longitudinal ridging, thinning, and pterygium (forward growth of cuticle scarring matrix). Alopecia areata causes trachyonychia (rough sandpaper appearance, 20-nail dystrophy in children). Onychomycosis shows distal-lateral subungual yellowish discoloration, hyperkeratosis, and onycholysis. Trauma produces subungual hematomas, splinter hemorrhages, and onychomadesis. Systemic diseases cause Beau lines (transverse depressions from systemic illness or chemotherapy), koilonychia (spoon-shaped, iron deficiency), Terry's nails (proximal white in cirrhosis), Lindsay's nails (half-and-half in renal failure), and clubbing (cardiopulmonary disease).
Diagnosis uses dermoscopy (onychoscopy) for capillary patterns and trichoscopic features, KOH preparation with fungal culture or PCR for onychomycosis, and nail unit biopsy (matrix or bed punch biopsy) when diagnosis is uncertain or for tumor exclusion. Treatment is etiology-specific: topical or intralesional corticosteroids and topical calcipotriol for psoriasis; intralesional triamcinolone for lichen planus; oral terbinafine or itraconazole for onychomycosis; iron supplementation for koilonychia; nail care education (avoid trauma, moisturize cuticles). Cosmetic camouflage (nail polish, prosthetic nails) can be used during treatment. Improvement requires months due to slow nail growth (fingernails 0.1 mm/day, toenails slower).