What causes dark nail tips and how are they treated?

Dark Nail Tips: Causes and Treatment

Immediate Diagnostic Priority

The primary concern with dark nail tips is ruling out nail unit melanoma, which requires nail matrix biopsy by a practitioner skilled in nail apparatus procedures for any suspicious lesions. 1 Delaying biopsy in suspicious lesions can impact survival outcomes, and early detection is critical. 1

Differential Diagnosis by Color Pattern

Brown-Black Pigmentation (Melanonychia)

• Malignant melanoma presents with irregular borders, width >5mm, progressive darkening, nail dystrophy, or pigment extending onto periungual skin (Hutchinson's sign) 2, 3
• Benign melanocytic lesions (nevi, lentigines) typically show regular borders, stable appearance, and width <5mm 3
• Inflammatory causes including psoriasis and lichen planus can produce longitudinal pigmentation with associated nail thinning and ridging 1, 4

Green-Black Discoloration

• Bacterial infection (Green Nail Syndrome) from Pseudomonas aeruginosa or Proteus species presents with greenish-black hue, typically confined to lateral nail edges 2, 1
• Treatment requires keeping the area dry and applying topical povidone iodine 2% twice daily 5, 1

Yellow-Brown-Black Discoloration

• Fungal infection (onychomycosis) causes thickening, discoloration, and friable texture, most commonly affecting toenails 6
• Distal and lateral subungual onychomycosis (DLSO) is the most common pattern, with fungus invading through distal or lateral margins 6

Diagnostic Algorithm

Step 1: Clinical Assessment

• Measure band width (>5mm suggests malignancy) 2
• Check for Hutchinson's sign (periungual pigment extension) 2
• Assess for nail dystrophy, bleeding, or irregular borders 2
• Examine all nails and check family members for fungal infections 5

Step 2: Laboratory Confirmation

• For suspected fungal infection: Direct microscopy with potassium hydroxide (KOH) preparation and fungal culture on Sabouraud's glucose agar are essential, as 50% of dystrophic nails are non-fungal despite similar appearance 5, 1
• For suspected melanoma: Nail matrix tangential excisional biopsy is the gold standard 3
• For bacterial infection: Culture if infection suspected 6

Step 3: Onychoscopy (if available)

• Useful initial diagnostic tool to aid in biopsy planning and patient triage 3
• Can help differentiate benign from malignant lesions before invasive procedures 3

Treatment Based on Confirmed Etiology

Fungal Infection (After Mycological Confirmation)

First-line treatment options:

• Terbinafine: Weight-based dosing: <20kg = 62.5mg daily; 20-40kg = 125mg daily; >40kg = 250mg daily 5, 7

  • Duration: 6 weeks for fingernails, 12 weeks for toenails 5, 7
  • Cure rate: 88% 5
  • Mycological cure demonstrated in 70-79% of patients 7

• Itraconazole pulse therapy: 5mg/kg/day for 1 week per month 5

  • Duration: 2 pulses (2 months) for fingernails, 3 pulses (3 months) for toenails 5
  • Cure rate: 94-100% 5, 1

Monitoring requirements:

• Baseline liver function tests and complete blood count before starting terbinafine 5
• Monitor liver function tests for patients on itraconazole, particularly with continuous therapy >1 month 5

Bacterial Infection

• Keep affected area dry 5, 1
• Apply topical povidone iodine 2% twice daily 5, 1
• Oral antibiotics if grade 2 or higher severity 6

Inflammatory Conditions (Psoriasis, Lichen Planus)

• For <3 nails affected: Intralesional triamcinolone acetonide 5-10mg/cc for nail matrix involvement 4, 1
• Topical steroids with or without vitamin D analogs for nail bed involvement 4, 1

Malignant Melanoma

• Excision with appropriate margins based on staging 1
• Longitudinal excision recommended for high-likelihood invasive melanoma to assess tumor extension 3

Critical Pitfalls to Avoid

• Never diagnose fungal infection based on appearance alone - 50% of dystrophic nails are non-fungal, requiring KOH and culture confirmation 5, 1
• Never delay biopsy in suspicious melanonychia - inadequate or delayed biopsy can miss invasive melanoma and impact survival 1
• Never overlook family examination - household transmission of fungal infections is common 5
• Never use superficial sampling technique for suspected melanoma - ensure practitioner expertise in nail apparatus procedures 1

Preventive Measures

• Apply daily topical emollients to cuticles and periungual tissues 6, 4
• Use protective nail lacquers to limit water loss 6
• Avoid nail trauma, biting, prolonged water soaking, and harsh chemical exposure 6, 4
• Wear comfortable well-fitting shoes and cotton socks 6
• Apply regular antifungal powder inside shoes for fungal prevention 5