If melanonychia is secondary to systemic and/or dermatologic disease, treatment of the underlying condition is helpful.
If melanonychia is secondary to a drug, discontinuation of the offending agent may result in clearance.
For invasive melanoma, amputation of the distal phalanx may be indicated.  Albeit controversial, total nail bed excision and reconstruction using a full-thickness graft may be considered. In a large case series, the 5-year survival rates for cutaneous melanoma of the hand versus subungual melanoma treated with a wide local excision was reported as 100% and 80%, respectively.  . This was due to a delay in diagnosing subungual lesions, which averaged 3.68 mm in depth versus 1.36 mm for hand melanomas of the cutaneous surface.
Because diagnosis is often delayed in these patients, sentinel lymph node biopsy after surgery may be warranted. 
Because longitudinal melanonychia is associated with a variety of systemic conditions, these cases may require referral to the appropriate specialist in order to manage the primary disease.
In cases of subungual melanoma with a poor prognosis, consultation with a hematologist/oncologist regarding potential chemotherapeutic options may be warranted.
Postoperative nail dystrophy is a common complication and should be taken into consideration before a nail biopsy is performed.  Postoperative nail dystrophy is less likely to occur with biopsies of the distal matrix than biopsies of the proximal matrix.
Complete excision when longitudinal melanonychia is located in the lateral third of the nail unit with a lateral longitudinal excision is a sampling method that may result in less cosmetic deformity than other methods.
Patients with longitudinal melanonychia of a single digit who decline a biopsy should receive close follow-up with their dermatologist, and monitoring of the melanonychia should be part of a routine monthly self-skin examination. Additionally, the physician may use a dermatoscope to monitor melanonychia.
If changes suggestive of melanoma are observed, a biopsy should be performed.
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