What is the best course of treatment for a patient with horizontal nail deformities, potentially caused by fungal infections, nail plate trauma, or underlying systemic conditions such as psoriasis or eczema?

Horizontal Nail Deformities: Treatment Approach

For horizontal nail deformities, first confirm the underlying cause through mycological testing (KOH preparation and fungal culture) if fungal infection is suspected, then treat accordingly: systemic terbinafine 250 mg daily for 6 weeks (fingernails) or 12 weeks (toenails) for confirmed onychomycosis, or intralesional triamcinolone 5-10 mg/cc for inflammatory conditions like psoriasis affecting the nail matrix. 1, 2, 3

Diagnostic Approach

The critical first step is distinguishing between infectious and non-infectious causes, as approximately 50% of dystrophic nails are non-fungal despite similar clinical presentation 4:

• Examine nail texture carefully: Soft, friable texture with thickening and yellow-brown discoloration suggests fungal infection (onychomycosis), while hard, brittle texture indicates non-infectious causes like psoriasis or lichen planus 1, 2, 4

• Assess for paronychia: Swelling and erythema of the nail fold suggests Candida infection, particularly in patients with occupational moisture exposure 1, 2

• Look for associated findings: Green or black discoloration indicates bacterial superinfection (typically Pseudomonas), while pitting and subungual hyperkeratosis suggest psoriasis 1, 2

• Obtain mycological confirmation before treatment: Collect specimens from discolored, dystrophic, or brittle parts of the nail, cutting through the entire thickness including crumbly material, for KOH preparation and fungal culture on Sabouraud's glucose agar 1, 2, 4

Critical pitfall: Never assume fungal infection without laboratory confirmation—clinical diagnosis alone is insufficient to distinguish infection from dermatological diseases like psoriasis or trauma 2, 4, 5

Treatment Algorithm by Etiology

Confirmed Fungal Infection (Onychomycosis)

Systemic therapy is the gold standard for horizontal nail deformities caused by dermatophyte infection:

• Terbinafine 250 mg orally once daily: 6 weeks for fingernail infections (79% mycological cure rate) or 12 weeks for toenail infections (70% mycological cure rate) 3

• Monitor liver function: Measure serum transaminases (ALT and AST) before initiating treatment, as hepatotoxicity occurs in approximately 1 in 2000 patients 3, 6

• Set realistic expectations: Optimal clinical effect occurs months after treatment completion due to time required for healthy nail outgrowth—approximately 10 months for toenails and 4 months for fingernails 3

• Topical therapy limitations: Amorolfine 5% lacquer or ciclopirox 8% lacquer applied once or twice weekly achieves only 30-50% cure rates and should be reserved for early disease affecting <80% of nail plate without lunula involvement 1, 6

Inflammatory Conditions (Psoriasis, Lichen Planus)

For horizontal ridging, pitting, and dystrophy from inflammatory dermatoses:

• Intralesional triamcinolone acetonide 5-10 mg/cc for nail matrix involvement when fewer than 3 nails are affected 2, 7

• Topical corticosteroids with or without vitamin D analogs for nail bed involvement 2, 8

• Consider systemic therapy (cyclosporine or biologic agents) for extensive disease affecting multiple nails 8

Important distinction: Lichen planus produces thinning of the nail plate with subungual hyperkeratosis and longitudinal ridging, which can progress to twenty-nail dystrophy requiring prolonged treatment (12 months for toenails, 6 months for fingernails to grow out completely) 2, 7

Candida Infections

Candida paronychia with secondary nail involvement requires different management:

• Topical povidone iodine 2% twice daily for localized paronychia 1, 2

• Oral azoles (ketoconazole, itraconazole) are more effective than terbinafine for Candida nail infections, though they carry risk of serious adverse effects and drug interactions 6

• Address occupational factors: Patients with chronic moisture exposure need guidance on protective measures like wearing gloves while cleaning 2

Supportive Care Measures (All Etiologies)

Regardless of underlying cause, implement these protective strategies:

• Apply daily topical emollients to periungual folds, nail matrix, and nail plate to maintain hydration 1, 2

• Use protective nail lacquers to limit water loss from the nail plate 1, 2

• Gently file nail surfaces with an emery board after softening in warm water to reduce thickness 2

• Avoid trauma: No nail biting, using nails as tools, prolonged water soaking, or exposure to harsh chemicals 1, 2

• Apply urea-based keratolytic cream daily to reduce nail thickness if needed 2

Medication-Induced Horizontal Ridges

For chemotherapy-related nail changes (particularly taxanes):

• Daily dilute vinegar soaks to nail folds twice daily for 10-15 minutes 2

• Mid to high potency topical steroid ointment to nail folds twice daily 2

• Consider temporary dose adjustment of causative medication in consultation with prescribing physician 2

• Prophylactic measures: Daily emollients, protective nail lacquers, and cotton gloves before starting taxane therapy 1

Key caveat: Taxane-related onycholysis is dose-dependent and more common with weekly paclitaxel regimens, with all-grade incidence of 43.7% for paclitaxel and 34.9% for docetaxel 1

When to Suspect Non-Dermatophyte Moulds

Consider non-dermatophyte moulds (accounting for 5% of UK cases, 20% of North American cases) when 1, 2:

• Previous antifungal treatment has failed repeatedly
• Direct microscopy is positive but no dermatophyte isolated
• No associated skin infection is present

These infections do not respond to conventional antifungal drugs and require specific identification for appropriate treatment 5