Nail disorders affect 10% of the population and are among the most clinically underappreciated conditions — both because they are often misdiagnosed (50% of dystrophic nails diagnosed as onychomycosis are actually other conditions — psoriasis, trauma, or lichen planus) and because they can be the first visible sign of significant systemic disease. A systematic approach to nail assessment — both for cosmetic conditions and as part of a comprehensive physical examination — adds clinical value disproportionate to the time invested.
Onychomycosis: Diagnosis and Treatment
Nail fungal infection (predominantly Trichophyton rubrum) affects 5.5% of the general population and 20% of adults >60. The critical first step: confirm diagnosis before treating. Culture, PAS-stained nail clipping, or PCR (highest sensitivity/specificity) — do not treat empirically as 50% of "thick yellow nails" are not onychomycosis and will not respond to antifungals. Oral terbinafine (Lamisil): 250mg daily × 6 weeks (fingernails) or 12 weeks (toenails). Mycological cure rates: 76–80% for fingernails, 59–70% for toenails — the most effective oral antifungal option. Drug interaction: inhibits CYP2D6 — check interactions before prescribing. Liver toxicity rare but requires monitoring in at-risk patients. Efinaconazole 10% topical (Jublia): FDA-approved topical antifungal for mild-moderate toenail onychomycosis. Mycological cure 53% at 52 weeks versus 17% vehicle — significantly more effective than older topicals (ciclopirox 8% cure rate ~30%). Laser therapy: Nd:YAG laser for onychomycosis — meta-analysis shows modest but real improvement, generally inferior to systemic antifungals but useful when systemic agents are contraindicated.
Nail Signs of Systemic Disease
Terry's nails (2/3 white, 1/3 pink-red distal band): cirrhosis, CHF, DM, aging. Beau's lines (transverse grooves): systemic illness, chemotherapy, zinc deficiency — time the illness by calculating nail growth rate (3mm/month fingernail). Lindsay's nails (half-and-half: proximal white, distal red-brown): chronic kidney disease. Mees' lines (transverse white bands): arsenic poisoning, chemotherapy. Yellow nail syndrome (thickened, yellow-green, slow-growing): lymphedema, pleural effusion, bronchiectasis. Clubbing: chronic hypoxic lung disease, cyanotic congenital heart disease, IBD, hepatic cirrhosis. Nail pitting: psoriasis (>50 pits is highly specific). Longitudinal melanonychia: normally present in darker skin (Fitzpatrick V-VI); new in lighter skin types requires dermoscopy to rule out subungual melanoma. For clinical facilities managing dermatological and systemic conditions, our laboratory supplies section supports nail culture collection and specimen processing.
