From the Guidelines
Longitudinal melanonychia should be evaluated by a dermatologist, particularly in adults, to rule out subungual melanoma, and a nail matrix biopsy may be necessary in suspicious cases, as recommended by the most recent guidelines 1. The condition can be benign or potentially malignant, with common benign causes including racial/ethnic predisposition, trauma, medication use, pregnancy, or inflammatory conditions. However, it's crucial to note that longitudinal melanonychia can sometimes indicate subungual melanoma, especially when it appears suddenly in a single digit, shows color variation, or is accompanied by nail dystrophy. Some key points to consider in the evaluation of longitudinal melanonychia include:
- The presence of ulceration, bleeding, or a nodule, which may indicate transformation to invasive carcinoma, as noted in the British Association of Dermatologists' guidelines for the management of squamous cell carcinoma in situ (Bowen's disease) 1.
- The importance of careful monitoring for changes in appearance, width, or color, and the potential need for dermoscopy or nail matrix biopsy to rule out melanoma in suspicious cases.
- The recommendation for a narrow excisional/complete biopsy with 1- to 3-mm margins that encompass the entire breadth of the lesion, as outlined in the guidelines of care for the management of primary cutaneous melanoma 1.
- The need for a practitioner skilled in biopsy of the nail apparatus to evaluate and sample suspicious nail lesions, due to the complexity of nail anatomy and the fact that melanoma arises in the nail matrix 1.
From the Research
Definition and Causes of Longitudinal Melanonychia
- Longitudinal melanonychia (LM) is a brown-black band on 1 or multiple nails, commonly encountered in clinical practice 2.
- Benign LM may be due to exogenous (external, blood, bacterial, mycotic) or endogenous (melanin) pigment 2.
- Melanin-derived LM may result from overproduction of melanin by a normal number of melanocytes (melanocytic activation) due to physiologic, local, systemic, iatrogenic, syndromic, and drug-induced causes, or from benign (nail matrix nevus and lentigo) or malignant (nail unit melanoma [NUM]) melanocyte hyperplasia 2.
Diagnosis and Evaluation of Longitudinal Melanonychia
- A high index of suspicion is necessary to differentiate benign LM and NUM secondary to similarities in clinical presentation, especially in pediatric patients 2.
- Onychoscopy and histopathologic examination of nail clippings are useful initial diagnostic tools for LM, avoiding a biopsy or aiding in biopsy planning and patient triage 2.
- Nail matrix excisional biopsy is the gold standard for diagnosing/ruling out NUM 2.
- For suspicious LM, a nail matrix tangential excisional biopsy is recommended 2.
- Biographical, clinical and dermoscopic criteria make it possible to suspect melanoma and decide whether to perform biopsy 3.
Treatment and Management of Longitudinal Melanonychia
- The biopsy technique should enable reliable histological study while limiting the risk of secondary nail dystrophy 3.
- Initial resection should ideally involve the entire lesion 3.
- Complete elevation of the nail plate enables the lesion to be precisely located 3.
- Lesions up to 3 mm can be removed by longitudinal resection biopsies without significant sequelae 3.
- In clinical presentations strongly suggestive of melanoma, immediate complete resection of the entire nail unit may be proposed 3.
- Treatment is as conservative as possible in order to keep the tip of the digit; once the melanoma is completely removed, amputations have not been shown to prolong the disease-free survival time 4.
Risk Factors and Prognosis of Longitudinal Melanonychia
- Malignant melanoma of the nail confers a higher mortality rate compared to other cutaneous melanomas, which is often attributable to delayed diagnosis 5.
- Two-thirds of nail melanomas present as longitudinal melanonychia (LM), longitudinally-oriented brown-black bands of pigment in the nail plate 5.
- Subungual melanoma is a rare malignancy, and diagnosis is often delayed, resulting in a higher staging and poorer prognosis than other cutaneous melanomas 6.