Distribution of cellular remnants of melanocytes in the nail plate: Clue to the diagnosis of subungual melanoma

Evaluation and diagnosis of longitudinal melanonychia: A clinical review by a nail expert group

Longitudinal melanonychia (LM), a brown-black band on 1 or multiple nails, is commonly encountered in clinical practice. Benign LM may be due to exogenous (external, blood, bacterial, mycotic) or endogenous (melanin) pigment. Histopathologically, 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. A high index of suspicion is necessary to differentiate benign LM and NUM secondary to similarities in clinical presentation, especially in pediatric patients. Benign pediatric LM may exhibit clinical and onychoscopic features resembling adult NUM; thus, a conservative approach with close follow-up is recommended. 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. Nail matrix excisional biopsy is the gold standard for diagnosing/ruling out NUM. For suspicious LM, a nail matrix tangential excisional biopsy is recommended. A longitudinal excision is recommended for cases with a high-likelihood of invasive NUM, which provides information on tumor extension. Herein, we review the current literature to describe the evaluation and diagnosis of LM.

Slow Mohs micrographic surgery for nail apparatus melanoma in situ

BACKGROUND

Nail apparatus melanoma is a malignant tumor with a high incidence in Chinese melanoma patients. Slow Mohs micrographic surgery is an emerging technique for treating nail apparatus melanoma in situ (NAMIS).

OBJECTIVE

This study evaluated the efficacy and safety of slow Mohs micrographic surgery for treating NAMIS.

METHODS

Patients were enrolled in this retrospective study and treated in a single center from October 1, 2016, to June 30, 2022. Each patient underwent standard slow Mohs micrographic surgery, and follow-up was regularly conducted at clinics.

RESULTS

Ten patients were enrolled in the study. Two patients underwent one Mohs stage, seven underwent two Mohs stages, and one underwent seven Mohs stages. The resection margin ranged from 5 to 25 mm. No severe complications were reported in the treatment, and recurrence of NAMIS was not observed during the follow-up period.

CONCLUSION

Slow Mohs micrographic surgery is a valuable surgical method to treat NAMIS that preserves digit function and can be well tolerated by patients.

A call for nail clipping histopathology to become an essential component of the routine evaluation of melanonychia: Benefitting patients as a triage and surgical planning maneuver

We call on dermatologists and dermatopathologists to include nail clipping histopathology as an essential component of the routine evaluation of melanonychia. This manuscript demonstrates a case where an adult woman with broad melanonychia of the right thumbnail declined a nail matrix biopsy, but was amenable to a nail clipping.The nail clipping showed pigmentation, melanocyte remnants, and small cavities in the nail plate. These features have been published previously by our group as a clue to nail unit melanoma within nail clippings.This patient was rapidly triaged for nail matrix biopsy, which demonstrated nail unit melanoma in situ. Every patient with melanonychia can benefit from a nail clipping by examination of the location of the pigmentation within the nail plate for surgical planning, and if melanocyte remnants are detected, the nail clipping also serves as a rapid triage mechanism for nail matrix biopsy to evaluate for nail unit melanoma. Fontana-stained sections will highlight the pigmentation in the nail plate, and its location in the nail plate can easily be described by the dermatopathologist. Nail clippings performed in the setting of clinically apparent melanonychia may show helpful histopathologic findings of pigmented fungi, hemorrhage, external pigmentation, features of other pigmented nail unit tumors, as well as other entities. Nail clipping histopathology can provide extensive information in the evaluation of melanonychia with minimal discomfort for a patient, and little disruption to a physician's clinic flow. With this additional case of a nail unit melanoma diagnosed after initial concern found in a nail clipping, as well as other information in the literature, it is clear that melanocyte remnants found in nail clippings are reliable concerning features related to nail unit melanoma in adults. With knowledge of these histopathologic features in nail clippings and the significance of melanocyte remnants, the dermatopathologist can play a crucial role in the use of a nail clipping as a life-saving diagnostic maneuver. Accordingly, given the potential benefit to patients in this setting, as well as other uses of a nail clipping in the evaluation of melanonychia, we call on dermatologists and dermatopathologists to innovate the routine evaluation of melanonychia through the routine employment of nail clippings for histopathologic evaluation.