What is the evaluation and treatment approach for transversal melanonychia?

Transversal Melanonychia: Evaluation and Treatment

Critical Distinction: Transverse vs. Longitudinal Melanonychia

Transverse melanonychia (horizontal pigmented bands across the nail) is fundamentally different from longitudinal melanonychia and requires a distinct diagnostic approach focused on systemic causes and medication effects rather than melanoma risk. 1

Evaluation Approach

Primary Etiologies to Investigate

Medication-induced causes are the most common etiology for transverse melanonychia, particularly chemotherapeutic agents:

• Taxanes (docetaxel, paclitaxel) are the leading cause, producing transverse pigmented bands as part of a constellation of nail toxicities 2, 1
• Other chemotherapeutic agents including capecitabine, etoposide, cytarabine, cyclophosphamide, and doxorubicin can cause transverse pigmentation 2
• Targeted therapies including mTOR inhibitors, EGFR inhibitors, and MEK inhibitors may produce transverse nail changes 2

Clinical Assessment

Obtain a detailed medication history as the first diagnostic step, focusing on:

• Current and recent chemotherapy regimens (within past 3-6 months) 2, 1
• Timing of pigmentation onset relative to treatment initiation 1
• Presence of other nail changes including onycholysis, brittleness, or periungual inflammation 2, 1

Examine all nails systematically to determine:

• Whether multiple nails are affected (suggests systemic cause) versus single digit (raises concern for other pathology) 3, 4
• Presence of associated findings such as onycholysis, subungual hyperkeratosis, or nail plate separation 2
• Signs of infection including erythema, swelling, or discharge 2

Diagnostic Testing

Biopsy is NOT indicated for transverse melanonychia when a clear medication or systemic cause is identified, as the pigmentation pattern itself excludes melanoma of the nail matrix (which presents longitudinally) 3, 5

Consider fungal and bacterial cultures only if:

• Clinical signs of superinfection are present 2
• The diagnosis remains unclear after medication review 2

Treatment and Management

For Medication-Induced Transverse Melanonychia

Preventive measures should be implemented at treatment initiation for patients receiving high-risk chemotherapy:

• Frozen gloves (10-30°C for 90 minutes during infusion) significantly reduce taxane-induced nail changes 1
• Daily application of topical emollients to periungual folds, nail matrix, and nail plate 6, 1
• Protective nail lacquers to limit water loss from the nail plate 6, 1
• Avoidance of nail trauma, excessive water exposure, and harsh chemicals 6, 1

Supportive Care

Once transverse melanonychia has developed:

• Continue emollient application to prevent secondary complications 6, 1
• Protect nails from trauma by wearing comfortable, well-fitting shoes and avoiding tight gloves 2
• Monitor for secondary bacterial or fungal superinfection, which occurs in up to 25% of chemotherapy-related nail changes 2
• Reassure patients that pigmentation typically resolves gradually after discontinuation of the causative agent 1

When to Escalate Care

Refer for nail unit biopsy if:

• A single digit develops new longitudinal (not transverse) melanonychia in an adult without clear systemic cause 2, 3
• Pigmentation extends onto periungual skin (Hutchinson's sign) 5, 4
• No medication or systemic cause can be identified after thorough evaluation 3, 4

Key Clinical Pitfalls

Do not confuse transverse with longitudinal melanonychia - the orientation is critical for determining melanoma risk. Longitudinal bands require biopsy consideration; transverse bands do not when a systemic cause is identified 3, 5

Do not perform nail matrix biopsy for transverse pigmentation - this causes permanent nail dystrophy and is unnecessary when the pattern indicates systemic rather than matrix-based pathology 2, 5

Do not overlook medication history - diagnostic delays averaging 2 years occur in nail melanoma cases, but this is relevant for longitudinal presentations; transverse melanonychia from medications is often mismanaged by unnecessary biopsies rather than appropriate supportive care 4