Longitudinal melanonychia may represent a heterogeneous group of conditions, from primary melanocytic causes to fungal/bacterial infections, hemorrhage, and exogenous causes, among others. The dermatologist's job is to diagnose nail melanoma.
Too often early nail melanoma, presenting as longitudinal melanonychia, is observed rather than biopsied. Clinically differentiating benign from malignant is difficult. Biopsy and pathologic examination remains the gold standard for diagnosis. Earlier biopsies diagnose earlier melanoma.
Digital myxoid cysts represent ganglions from the DIPJ. Most treatments, one way or another, involve scarring the stalk that extends from the joint to the tissues around the nail.
Nail squamous cell carcinoma is usually associated with HPV-16. It is difficult to clinically differentiate refractory-to-treatment ungual/periungual warts from carcinoma. Only biopsy with depth can make this diagnosis reliably.
Midline nail dystrophies are often confusing, with habit tic deformity and median canaliform dystrophy occasionally demonstrating overlap features. Careful examination can usually distinguish the two.