Longitudinal erythronychia is a linear red band of the nail plate. This finding is becoming increasingly recognized in clinical practice. Neoplastic, inflammatory, scarring, or idiopathic processes involve the distal nail matrix, producing a groove in the ventral nail plate. The nail bed then occupies this groove and accentuates the red color of the nail bed, producing a red streak.

Longitudinal erythronychia may be specific to one nail or involve multiple nails.

When longitudinal erythronychia involves one nail, it may be caused by benign conditions, such as onychopapilloma, wart, warty dyskeratoma, glomus tumor, or a solitary lesion of lichen planus. Less commonly, it may be caused by malignancies, such as Bowen disease, invasive squamous cell cancer, melanoma in situ, and basal cell carcinoma.

The most common causes of longitudinal erythronychia involving multiple nails are lichen planus and Darier disease. Less common etiologies are systemic amyloidosis, hemiplegia, graft-versus-host disease, and acantholytic epidermolysis bullosa.

Longitudinal erythronychia presents most commonly in adults around 60 years of age, and the thumb is most frequently involved. It may be asymptomatic or painful. A split nail is an associated physical finding.