Subungual Melanomas

Subungual melanomas:
- Are rare subtypes of melanoma:
  - Accounting for 0.7% to 3.5% of all reported cases
  - The hallux and thumb are the most commonly affected sites
- Antecedent trauma:
  - Has been reported in 25% to 55% of patients
- Diagnosis is often delayed because of:
  - Inadequate biopsies
  - Lesion neglect
  - Confusion with benign melanonychia, hematoma, chronic trauma, or fungal nail infection (onychomycosis)
The classic features suggestive of melanoma include:
- Melanotic lesions arising from the nail matrix and longitudinal melanonychia:
  - Defined as a band of pigmentation extending from the proximal nail fold / lunula throughout the nail to the free edge
  - Any band greater than 3 mm in width or associated with discoloration of the lateral or proximal nail folds (Hutchinson’s sign):
    - Mandates biopsy of the nail matrix and bed with either incisional or punch techniques:
      - Partial or total avulsion of the nail plate is usually needed to perform biopsy
Management of these lesions requires sound oncologic resection with consideration of functional deficits:
- Margin principles in melanoma are maintained:
  - Which means amputation is often necessary
- Special consideration is given to the hallux and thumb:
  - As the complete loss of either can cause substantial disability
- For the hallux amputation of the digit preserves the metatarsal head, and for the thumb, efforts are made to preserve bone proximal to the interphalangeal joint, if appropriate margins allow:
  - Excision of the nail bed, matrix, and proximal nail fold will not provide adequate margins
Mohs micrographic surgery has been used in several small series for selected cases of melanoma-in-situ only, and this technique would not provide adequate resection of this melanoma deeper melanomas
Amputation of the thumb just proximal to the interphalangeal joint is the best approach:
- As it provides for adequate margins while preserving a stump for some functional use. Radical amputation would also provide adequate margins, but the functional deficit created is unnecessary
References:
- Ross MI. Excision of primary melanoma. In: Balch CM, Houghton AN, Sober AJ, Soong S-J, eds. Cutaneous Melanoma. 5th ed. St. Louis: Quality Medical Publishing; 2009:251-274.
- Sureda N, Phan A, Poulalhon N, Balme B, Dalle S, Thomas L. Conservative surgical management of subungal (matrix derived) melanoma: report of seven cases and literature review. Br J Dermatol. 2011;165:852-858.
- Tan KB, Moncrieff M, Thompson JF, et al. Subungual melanoma: a study of 124 cases highlighting features of early lesions, potential pitfalls in diagnosis, and guidelines for histologic reporting. Am J Surg Pathol. 2007;31:1902-1912.