Melanonychia Clinical Presentation

Most melanonychia patients present with a history of asymptomatic hyperpigmentation of the nail plate.

A careful history should include information on medications, past treatments, hobbies and illnesses, family history, any history of trauma to the area, prior history of a biopsy of the nail unit, number of nails affected, results of any prior nail clippings sent for histologic examination, results of cultures sent for infectious organisms, change of appearance of the band (or bands) over time, and racial origin.^[12]

In cases of subungual melanoma, the patient may describe a long-standing history of longitudinal melanonychia that recently changed in appearance. Changes that warrant concern include alteration of color, pattern, or size of the band; new onset of pain or ulceration in the site of longitudinal melanonychia;^[13] or the presence of subungual blood.^[14]

Melanonychia is characterized by a tan, brown, or black discoloration of the nail unit and is often observed in the nail plate. The nail plate may be diffusely involved, or only a single longitudinal band may be present. Transverse melanonychia has also been rarely reported. One or more digits may be involved.

Levit et al identified characteristics of melanonychia that should warrant concern for subungual melanoma, and they used the acronym ABCDEF to describe them, as follows^[15] :

• (A) Age: The peak incidence in the fifth to seventh decade of life. Additionally, subungual melanoma accounts for one third of melanoma cases in Asians, African Americans, and Native Americans.
• (B) Brown-black band with breadth greater than 3 mm with variegated borders
• (C) Change in nail band morphology despite treatment
• (D) Digit involved: The thumb is more likely to be affected by subungual melanoma than the great toe; the great toe is more likely than the index finger to be affected by subungual melanoma.
• (E) Extension of the brown-black pigment of the nail bed, nail matrix, and/or nail plate onto the adjacent cuticle and proximal and/or lateral nail folds (Hutchinson sign)
• (F) Family or personal history of dysplastic nevus or melanoma

Careful examination of the oral and genital mucosa may provide important diagnostic clues to identify Peutz-Jeghers syndrome or Laugier-Hunziker syndrome.^[16]

When determining the etiology of longitudinal melanonychia, it is important to distinguish between melanocytic activation and melanocytic hyperplasia. Melanocytic activation is caused by an increased synthesis of melanin with a normal number of melanocytes. Melanocytic hyperplasia (including melanocytic nevi and melanoma) refers to an increased synthesis of melanin with an increased number of melanocytes. Nevi constitute 12% of longitudinal melanonychia cases in adults and 50% of longitudinal melanonychia cases in children. Note the clinical image below.

Approximately two thirds of cases have a brown-black color, and one third of cases have periungual pigmentation (benign pseudo-Hutchinson sign). The bands are wider than 3 mm in greater than 50% of cases.

Below are the causes of melanonychia.^{[1, 4, 17, 18]}

Melanocytic activation/hyperplasia–related causes are as follows:

• Nevi
• Melanotic macule of the nail unit
• Melanocytic activation
• Subungual melanoma

Physiologic causes of melanonychia are as follows:

• Racial melanonychia (African American, Hispanic, Indian, Japanese, other dark-skinned races) (multiple bands)
• Pregnancy (multiple bands)

Local and regional causes of melanonychia are as follows:

• Trauma (acute or chronic) (single band)
• Poor-fitting shoes (single band)
• Onychotillomania (single band)
• Nail biting (single band)
• Carpal tunnel syndrome (single band)
• Foreign body (subungual) (single band)
• Radiation therapy (multiple bands)
• Ultraviolet light (multiple bands)
• Postinflammatory hyperpigmentation (single band)

Systemic causes of melanonychia are as follows:

• Addison disease (multiple bands)
• Cushing syndrome (multiple bands)
• Nelson syndrome (multiple bands)
• Hyperthyroidism (multiple bands)
• Hemosiderosis (multiple bands)
• Hyperbilirubinemia (multiple bands)
• Alcaptonuria (multiple bands)
• Porphyria (multiple bands)
• Acquired immunodeficiency syndrome (multiple bands)
• Graft versus host disease (multiple bands)
• Malnutrition (multiple bands)
• Vitamin B-12 deficiency (multiple bands)

Dermatologic causes of melanonychia are as follows:

• Psoriasis (multiple bands)
• Lichen planus (multiple bands)
• Chronic radiodermatitis (single bands)
• Scleroderma (multiple bands)
• Systemic lupus erythematosus (multiple bands)
• Fungal infection of the nail bed (Aspergillus, Scopulariopsis, Candida, Blastomyces, Fonsecaea pedrosoi) (multiple bands)
• Basal cell carcinoma (single band)
• Bowen disease (single band)
• Subungual fibrous histiocytoma (single band)
• Mucous cyst (single band)
• Lichen striatus (multiple bands)

Iatrogenic causes of melanonychia are as follows:

• Chemotherapeutics (multiple bands)

  • Bleomycin sulfate
  • Busulfan
  • Cyclophosphamide
  • Dacarbazine
  • Daunorubicin hydrochloride
  • Doxorubicin
  • Etoposide
  • 5-Fluorouracil
  • Hydroxyurea
  • Melphalan hydrochloride
  • Methotrexate
  • Nitrogen mustard
  • Nitrosourea
  • Tegafur
• Others (multiple bands)

  • Corticotropin
  • Amodiaquine
  • Amorolfine
  • Arsenic
  • Chloroquine
  • Clofazimine
  • Clomipramine
  • Cyclines
  • Diquat
  • Fluconazole
  • Fluoride
  • Gold salts
  • Ibuprofen
  • Ketoconazole
  • Lamivudine
  • Mepacrine
  • Mercury
  • Minocycline
  • Melanocyte-stimulating hormone
  • Polychlorinated biphenyl (PCB)
  • Phenytoin
  • Phenothiazine
  • Psoralen
  • Roxithromycin
  • Steroids
  • Sulfonamide
  • Tetracycline
  • Thallium
  • Timolol
  • Zidovudine

Causes of melanonychia associated with a syndrome are as follows:

• Laugier-Hunziker syndrome (multiple bands)
• Peutz-Jeghers syndrome (multiple bands)
• Touraine syndrome (multiple bands)