What are the causes and treatment options for brown line pigmentation of the nail, also known as melanonychia?

Brown Line Pigmentation of the Nail (Melanonychia)

When evaluating brown line pigmentation of the nail, the primary concern is ruling out nail unit melanoma, which requires nail matrix biopsy by a practitioner skilled in nail apparatus procedures for any suspicious lesions. 1

Causes of Melanonychia

Benign Causes - Melanocytic Activation

• Ethnic/physiologic melanonychia is the most common cause in dark-skinned individuals and typically affects multiple nails 2
• Medication-induced pigmentation from chemotherapy agents, antimalarials, or other systemic drugs 2
• Inflammatory conditions including psoriasis and lichen planus can cause longitudinal pigmentation 3
• Trauma-related chronic local trauma to the nail matrix 2
• Systemic conditions such as pregnancy, endocrine disorders, Addison's disease, and syndromes like Peutz-Jeghers or Laugier-Hunziker 2

Benign Causes - Melanocytic Hyperplasia

• Nail matrix nevus presents as a stable, well-demarcated brown band 4
• Nail lentigo shows uniform pigmentation with regular borders 2

Malignant Cause

• Nail unit melanoma (subungual melanoma) is the critical diagnosis to exclude, as delayed recognition significantly impacts mortality 1

Non-Melanin Causes

• Fungal infections cause thickening, discoloration, and friable texture requiring KOH preparation and fungal culture for confirmation 3, 5
• Bacterial infections (Green Nail Syndrome from Pseudomonas) present with green-brown discoloration 3, 5
• Blood/hematoma from trauma shows characteristic evolution over time 6

Red Flags for Nail Unit Melanoma

The following features mandate biopsy evaluation: 2, 7

• Hutchinson sign - periungual spread of pigmentation onto cuticle, proximal or lateral nail folds
• Age and onset - abrupt appearance after age 50 or rapid change in existing band
• Band characteristics:
  • Width >3 mm
  • Irregular borders (blurry or variegated)
  • Color variegation within the band
  • Proximal widening (triangular shape)
• Single digit involvement in adults (multiple digits more likely benign)
• Associated nail dystrophy or irregular surface elevation
• Personal or family history of melanoma

Diagnostic Approach

Initial Evaluation

• Dermoscopy/onychoscopy is a useful screening tool to assess pigment pattern, though it cannot definitively rule out melanoma 4, 8
• Nail clipping histopathology can provide initial diagnostic information and aid in biopsy planning 4
• Examine for concomitant infections in other nails and family members if fungal etiology suspected 5

When to Biopsy

Any suspicious nail lesion (melanonychia striata, diffuse pigmentation, or amelanotic changes) requires nail matrix sampling by a practitioner skilled in nail apparatus biopsy. 1

• Nail matrix tangential excisional biopsy is recommended for suspicious lesions to obtain adequate tissue for diagnosis 4
• Longitudinal excision is preferred when high likelihood of invasive melanoma exists, as it provides information on tumor extension 4
• The nail plate must be sufficiently removed to expose the underlying lesion 1
• Avoid superficial shave biopsies as they may underestimate depth and stage 1

Pediatric Considerations

In children, a conservative wait-and-see approach with close follow-up is recommended for benign-appearing melanonychia, as pediatric lesions may exhibit features resembling adult melanoma but are rarely malignant. 4, 2

Treatment Based on Etiology

Benign Melanonychia

• Observation with serial photography for stable, benign-appearing lesions, especially in children and dark-skinned individuals 2
• Avoid trauma to the nail matrix area 2
• For inflammatory causes (psoriasis/lichen planus affecting <3 nails): intralesional triamcinolone acetonide 5-10 mg/cc for nail matrix involvement, or topical steroids with/without vitamin D analogs for nail bed involvement 3

Fungal Infection (if confirmed by culture)

• Pulse itraconazole 5 mg/kg/day for 1 week per month: 2 months for fingernails, 3 months for toenails (94-100% cure rate) 5
• Daily terbinafine for 6 weeks (fingernails) or 12 weeks (toenails): 62.5 mg/day if <20 kg, 125 mg/day for 20-40 kg, 250 mg/day if >40 kg (88% cure rate) 5
• Azoles are preferred when Candida species confirmed 5

Bacterial Infection

• Keep area dry and apply topical povidone iodine 2% twice daily for Green Nail Syndrome 3, 5

Malignant Melanoma

• Excision with appropriate margins based on staging, following melanoma management guidelines 1

Critical Pitfalls to Avoid

• Never diagnose fungal infection based on appearance alone - 50% of dystrophic nails are non-fungal despite similar presentation; always confirm with KOH and culture 5
• Do not assume benign etiology in adults with new single-digit melanonychia - this pattern warrants high suspicion for melanoma 2, 7
• Avoid inadequate biopsy technique - superficial sampling may miss invasive melanoma; ensure practitioner has expertise in nail apparatus procedures 1
• Do not delay biopsy in suspicious lesions - early detection of nail unit melanoma is critical for survival outcomes 1