Nail abnormalities may be an important clue to skin or systemic disease. Nail pits are seen in psoriasis or pemphigus. Psoriatic nails may show transverse nail grooves, shattered nail plates, or smooth white nails. Fissured hemorrhages are seen on the nail bed. About 5% of patients with lichen planus have nail changes. Longitudinal ridges or splitting of the nail are most common, as well as thinning of the nail, separation of the nail and reddening of the nail halves. In severe cases, the nail bed is disrupted by inflammation, there is fibrous tissue replacement, pterygium formation, and partial fusion of the proximal nail fold with the proximal nail bed. The nails of patients with follicular keratosis may show hyperkeratosis, brittleness, cracking, red and white cross stripes, and triangular defects at the free end. The most common cause of hooked nails is a claw-like or croton-shaped nail caused by prolonged failure to trim the nail.