Background: Longitudinal erythronychia (LE) is a term for red streaks in the nail. We describe the range of diseases manifested by localized (single or bifid) LE and explain the underlying physical changes.
Observations: Longitudinal erythronychia can be multiple or localized. Multiple lesions typically indicate an inflammatory disease such as lichen planus. When localized, they may be a single or bifid streak arising through a benign or malignant neoplasm, scarring of the dermis or epidermis, or the first stage of an inflammatory process that may evolve into multiple LE. Excision of a localized LE may provide a diagnosis and cure. Incisional matrix biopsy of multiple LE may provide a diagnosis. Clinical manifestation of LE arises through reduced compression of the nail bed due to loss of bulk of the nail plate with a groove on the undersurface. A streak of thinned nail then allows an enhanced view of a corresponding streak of engorged nail bed. The reduction in nail thickness renders it more fragile with a tendency to split distally.
Conclusions: Understanding LE can assist in diagnosis and explanation to the patient. Localized LE may represent a focal tumor or dysplastic process.