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INTRODUCTION

KEY POINTS

  • Longitudinal melanonychia (LM) is common in darker skin types, usually as a result of melanocyte activation.

  • Atypical LM may indicate nail apparatus melanoma (NAM).

  • Evaluation of LM for NAM includes a detailed history and physical examination, examination of all 20 nails, use of dermoscopy, and often a nail matrix biopsy.

  • NAM has a worse prognosis than its cutaneous counterpart in large part due to delayed diagnosis.

  • Lichen planus commonly causes LM in persons of color.

  • Lichen planus may cause irreversible scarring nail disease. Prompt treatment is imperative.

  • Lichen planus and psoriasis may both exist as a primary nail disease without cutaneous disease.

  • Psoriasis of the nail unit is difficult to treat primarily because of poor medication bioavailability.

  • Onychomycosis is the most common nail disorder.

Examination of the nails is an important part of the dermatologic examination in every skin phototype. There are very few unique nail changes and nail diseases in patients with darker skin phototypes. Nail unit melanocytes are usually quiescent in all skin types, and the clinical appearance of nails of different skin phototypes is closer than perhaps any other cutaneous structure [Figure 40-1]. This chapter highlights the examination of nails in skin of color, featuring melanonychia and nail apparatus melanoma (NAM). Other common nail disorders including lichen planus, psoriasis, and onychomycosis will also be covered.

FIGURE 40-1.

Skin phototype II (left) and V (right) index fingernails. The nail bed color is identical despite the different finger skin colors.

MELANONYCHIA

Melanonychia, or melanin-derived brown to black nail pigmentation, is an ambiguous clinical finding representing a diagnostic challenge for clinicians. Although the most serious disease of the nail unit, melanoma, presents with melanonychia in roughly two- thirds of cases, melanonychia also occurs as a result of other etiologies such as nail matrix melanocytic activation, benign nail matrix melanocytic hyperplasia, and nail invasion by melanin-producing pathogens.1 In addition, other nail pathogens, exogenous substances, and subungual hemorrhage can cause nonmelanic brown to black nail pigmentation.1,2,3

Regrettably, patients with NAM are often initially misdiagnosed.2 Due to diagnostic delays of an average of 2 years, NAM carries a poor prognosis, with reported 5- and 10-year survival rates of 30% and 13%, respectively.4,5 Some experts also contend that melanomas of the nail unit are more aggressive malignancies that metastasize earlier than cutaneous melanoma, with worse survival rates, stage for stage and thickness for thickness, than cutaneous melanomas.6,7 A thorough knowledge of the various causes of melanonychia and the use of a systematic approach when evaluating brown to black nail pigmentation may help prevent misdiagnosis and thereby improve prognosis.

Physiology

Nail plate melanin is primarily generated by nail matrix melanocytes.2...

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