Longitudinal Half-and-Half Nails: Case Report and Review.

Half-and-half nails were originally described as a transverse leukonychia in patients with chronic renal disease; other conditions (such as Behcet's and Crohn's disease) and medications (such as isoniazid) have also been associated with the nail changes. However, longitudinal half-and-half nails (affecting the medial aspects of the nails) have previously been reported on the great toes of an older woman and, in the present case, on the thumbs of an elderly man; neither person had Behcet's, Crohn's, or kidney disease or was receiving isoniazid. The woman had a true leukonychia, bilateral hallux valgus deformity, and chronic trauma to her medial nail folds. The man had a nontraumatic apparent leukonychia and bilateral koilonychia; the non-white lateral area of his left thumb also had a linear groove (resulting from a digital mucous cyst on the proximal nail fold) and subun gual hyperkeratosis. In conclusion, longitudinal half-and-half nails are a rare phenomenon that has not been associated with either a systemic disease or medication; the acquired nail change can present either as an idiopathic finding or occur secondary to chronic trauma.