What are the characteristics and management of Melanonychia (nail plate pigmentation)?

Melanonychia: Characteristics and Management

Melanonychia is characterized by brown to black pigmentation of the nail plate caused by melanin deposition, which can be due to benign causes in most cases but may also indicate subungual melanoma requiring prompt evaluation and management.

Clinical Presentation and Etiology

• Melanonychia typically presents as longitudinal melanonychia (LM), which appears as tan, brown, or black longitudinal streaks within the nail plate running from the proximal nail fold to the distal edge 1
• Two main mechanisms cause melanonychia: melanocytic activation (increased activity of normal melanocytes) and melanocytic hyperplasia (increased number of melanocytes) 2
• Common benign causes include:
  • Ethnic/racial melanonychia in dark-skinned individuals (most common cause) 1
  • Pregnancy, chronic trauma, infections 1
  • Medications, particularly taxanes and other chemotherapeutic agents 3
  • Systemic conditions including endocrine disorders, hemochromatosis, and Peutz-Jeghers syndrome 1

Differential Diagnosis

• It's essential to differentiate melanonychia from other nail conditions such as:
  • Subungual hematoma (blood collection under the nail) 4
  • Onychomycosis (fungal nail infection) 3
  • Onycholysis (separation of nail plate from nail bed), which may appear black, white, or brown-red 3

Evaluation and Assessment

• Suspicious features that may indicate subungual melanoma include:
  • Abrupt onset after middle age 1
  • Personal or family history of melanoma 1
  • Rapid growth or darkening of a melanonychia band 1
  • Pigment variegation or blurry lateral borders 1
  • Bandwidth >3 mm or proximal widening 1
  • Single digit involvement (rather than multiple) 1
  • Hutchinson sign (periungual spread of pigmentation onto adjacent cuticle and/or nail folds) 1
  • Associated nail plate dystrophy 1

Management Approach

• For benign-appearing melanonychia, especially in children, a wait-and-see approach with regular monitoring is appropriate 1
• Dermoscopy can be helpful in evaluating melanonychia, though its definitive benefit in screening lesions remains to be fully established 5
• Biopsy is indicated when:
  • Features suspicious for melanoma are present 6
  • There is uncertainty about the diagnosis 7
  • The lesion is changing rapidly 1

Biopsy Techniques

• Nail matrix biopsy is the gold standard for diagnosis of suspicious melanonychia 6
• The appropriate biopsy technique depends on:
  • Location of the pigmented band 6
  • Width of the band 6
  • Degree of clinical suspicion for melanoma 6

Prevention and Management of Medication-Induced Melanonychia

• For medication-induced melanonychia (particularly with taxanes):
  • Daily application of topical emollients on periungual folds, matrix, and nail plate 3
  • Use of protective nail lacquers to limit water loss from the nail plate 3
  • Avoiding nail trauma, excessive water exposure, and harsh chemicals 8
  • For taxane therapy, frozen gloves (10-30°C for 90 minutes) have shown significant reduction in nail changes 3

Follow-up

• Prolonged follow-up is mandatory for early detection of possible malignant changes in persistent melanonychia 1
• Patients with nail apparatus melanoma are often initially misdiagnosed, leading to diagnostic delays averaging 2 years, which contributes to poor prognosis 2
• Regular monitoring with clinical photography and dermoscopy can help detect changes over time 7

Special Considerations

• Melanonychia in children is almost always benign, but should still be monitored 1
• In patients receiving chemotherapy, particularly taxanes, melanonychia may be part of a constellation of nail changes including onycholysis 3
• Subungual melanoma carries a higher mortality rate compared to other cutaneous melanomas, often due to delayed diagnosis 6