What is the diagnosis and treatment for a painless blackish and atrophied nail?

Diagnosis and Management of Painless Blackish Atrophied Nail

The most likely diagnosis is onychomycosis (fungal nail infection), which requires laboratory confirmation before initiating systemic antifungal therapy with terbinafine or itraconazole. 1, 2

Differential Diagnosis

The painless blackish discoloration with nail atrophy requires consideration of several etiologies:

Primary Considerations

• Onychomycosis - Fungal infection presents with thickening, discoloration (including black), and friable texture of the nail plate, with toenails affected more commonly than fingernails (80% vs 20%) 1, 3

• Bacterial infection - Pseudomonas aeruginosa or Proteus species can cause green or black discoloration of nails, though this typically presents with moisture exposure history 1, 4

• Subungual melanoma - Must be excluded in any case of longitudinal melanonychia or persistent dark pigmentation, particularly as this accounts for 50% of melanomas in persons with dark skin 1, 5

Other Non-Infectious Causes

• Chronic trauma, psoriasis, lichen planus, and onycholysis can produce nail dystrophy mimicking fungal infection, though the nail surface typically does not become soft and friable as in onychomycosis 1

Diagnostic Workup

Laboratory confirmation is mandatory before treatment - never diagnose fungal infection based on appearance alone, as 50% of dystrophic nails are non-fungal despite similar clinical presentation. 4

Essential Investigations

• Potassium hydroxide (KOH) preparation with direct microscopy - Calcofluor white staining enhances visualization of fungal elements and increases sensitivity compared to standard KOH 1, 4

• Fungal culture on Sabouraud's glucose agar - Provides definitive identification of dermatophytes, Candida species, or non-dermatophytic molds, with results in 2-6 weeks 1, 4

• Nail biopsy with periodic acid-Schiff (PAS) staining - More sensitive than direct microscopy or culture, though not routinely available in most settings 1

Critical Pitfall to Avoid

• Do not assume fungal infection without laboratory confirmation, as approximately 50% of dystrophic nails have non-fungal etiologies requiring different management 4

• If melanoma is suspected based on pigmentation pattern, refer immediately to dermatology for nail biopsy 5

Treatment Algorithm

For Confirmed Onychomycosis

Systemic antifungal therapy is the treatment of choice for nail involvement:

• Terbinafine 250 mg daily - FDA-approved regimen: 6 weeks for fingernails, 12 weeks for toenails, with 70% mycological cure rate and 38% complete cure (mycological cure plus 0% nail involvement) 2

• Pulse itraconazole - Alternative regimen: 5 mg/kg/day for 1 week every month, for 2 months (fingernails) or 3 months (toenails), with 94-100% clinical cure rates 4

• Baseline liver function tests (ALT and AST) must be obtained before initiating terbinafine, with patient counseling to report symptoms of hepatotoxicity (persistent nausea, anorexia, fatigue, right upper abdominal pain, jaundice, dark urine, pale stools) 2

Adjunctive Measures

• Topical amorolfine 5% lacquer applied 1-2 times weekly for 6-12 months after gentle filing can be effective in approximately 50% of cases when less than 80% of nail plate is affected 3

• Mechanical debridement by expert podiatrist combined with urea-based keratolytic cream can reduce nail thickness 3

For Bacterial Infection (If Confirmed)

• Keep affected area dry and apply topical povidone iodine 2% twice daily 6, 4

Expected Timeline and Follow-Up

• Mean time to overall success is approximately 10 months for toenails and 4 months for fingernails after completing therapy 2

• Optimal clinical effect occurs months after mycological cure due to time required for outgrowth of healthy nail 2

• Clinical relapse rate is approximately 15% when evaluated at least 6 months after achieving clinical cure 2

Key Clinical Pearls

• Examine family members for fungal infections, as household transmission is common 4

• Check for concomitant infections such as tinea pedis or tinea capitis 4

• Advise patients to minimize exposure to natural and artificial sunlight during terbinafine treatment due to photosensitivity risk 2

• Discontinue treatment immediately if signs of serious adverse reactions develop, including hepatotoxicity, taste/smell disturbance, depressive symptoms, or severe cutaneous reactions 2