Melanonychia Striata Versus Onychomycosis: Nailing Down the Differences

Consultations & Comments

Reader Reaction and Timely Answers From Experts

Can fungal infections present with a brown band along the longitudinal axis of the nail similar to melanonychia striata but perhaps affect other digits?
—— Bea Maidana

The distinctive features of melanonychia striata usually allow a straightforward differentiation from onychomycosis.

MELANONYCHIA STRIATA
Also known as longitudinal melanonychia, melanonychia striata is characterized by a tan, brown, or black longitudinal streak within the nail plate (A).¹ The condition is noted more often in persons with deeply pigmented skin and is rare in whites. It is caused by an increased activity of melanocytes in the nail matrix with subsequent increased melanin deposition in the nail plate. In most cases, the occurrence is sporadic and there is no underlying pathology. Melanonychia striata is more common in the thumb, which is the most frequently used digit.² The index, middle, fourth, and fifth fingers grasp objects with decreased frequency and demonstrate a correspondingly lower incidence of melanonychia striata. Involvement of the toes or multiple digits is unusual.³

ONYCHOMYCOSIS
Onychomycosis may be caused by dermatophytes (tinea unguium); Trichophyton rubrum and Trichophyton mentagrophytes account for 80% to 90% of cases.⁴ Nondermatophyte molds that can cause onychomycosis include Acremonium species, Alternaria species, Aspergillus species, Fusarium species, Scytalidium species, and Scopulariopsis species.⁴ Candida albicans accounts for about 70% of cases of onychomycosis caused by yeasts. Predisposing factors include hyperhidrosis, wearing occlusive shoes, participationto fungi, nail trauma, immunodeficiency, diabetes mellitus, and old age.

Several clinical patterns of onychomycosis have been recognized, namely, distal subungual onychomycosis, proximal subungual onychomycosis, white superficial onychomycosis, and candidal onychomycosis. Distal subungual onychomycosis (B) is the most common form and is characterized by infection of the underside of the nail plate via the hyponychium that spreads to the matrix from distal to proximal.⁵ In contrast to melanonychia striata, onychomycosis more commonly involves toenails and often affects multiple digits.

Clinically, the affected nail has a whitish or yellowish appearance, although it may appear yellowish brown or black in onychomycosis caused by Scopulariopsis species and Scytalidium species.⁶ It is extremely unusual for onychomycosis to present as a tan, brown, or black longitudinal streak within the nail plate. In candidal onychomycosis, the entire nail may be affected. Other clinical features suggestive of onychomycosis include hyperkeratosis of the nail bed, onycholysis, subungual debridement, and thickening of the nail plate.⁷