melanonychia; longitudinal melanonychia; melanonychia striata

Etiology

• subungual melanoma
• physiologic longitudinal melanonychia
• systemic disorders
• trauma
• inflammatory disorders
• fungal infections
• drugs (azidothymidine, minocycline, antimalarials, gold, chemotherapy)
• benign melanocytic hyperplasias
• lentigo

Epidemiology

• prevalence increases with age
• more common in darker pigmented individuals
• ~100% of blacks > 50 years of age
• in the general white population, prevalence is 1.4%

Pathology

• increased production of melanin by melanocytes in nail matrix

Clinical manifestations

• asymptomatic brown or black pigmentation of the nail
• commonly presents as pigmented band arranged lengthwise along the nail
• longitudinal brown lines may extend from tip of nail into the lunula
• typically multiple nails are involved
• a single nail with longitudinal melanonychia suggests an underlying melanocytic lesion (subungual melanoma)
• suspect melanoma when proximal nail fold involved (Hutchinson's sign)

* images

Laboratory

• nail plate clipping for histologic analysis (KOH prep) & appropriate cultures if fungal infection suspected
• nail matrix biopsy if subungual melanoma suspected
  • > 3 mm in width
  • irregular or blurred borders to the band
  • brown black discoloration of the proximal nail fold (skin proximal to nail)

Differential diagnosis

• subungual melanoma is the most serious concern
  • acral lentiginous melanoma (periungual pigmentation or Hutchinson's sign)
• melanotic macule of the nail unit
• nail matrix nevus
• onychomycosis
• subungual hematoma

* also see brown nails

Management

• refer to dermatology if subungual melanoma suspected
• directed at underlying etiology
• no treatment indicated for benign etiology

More general terms

• melanocytic disorder
• brown nails; longitudinal brown lines; black nails

More specific terms

• Laugier-Hunziker syndrome