Psoriasis may affect any or all parts of the nail apparatus. Pitting is the most common abnormality. It affects finger nails more commonly than toe nails. Pits are often small, i.e. under 1 mm in size and can be shallow or deep seated. Pits are often irregularly or randomly arranged on one or more nails. Focal nail bed parakeratosis produces an oil spot or salmon patch. Subungual hyperkeratosis characterised by abnormal cornification of nail bed and hyponychium is seen. Splinter haemorrhages and nail plate thickening are also seen in psoriasis. A variety of nail changes are described in lichen planus. Bluish red discoloration of proximal nail folds is the earliest feature seen. The lunula may become red. Severe atrophy of proximal portions of the nail matrix results in irregular grooves, ridging with longitudinal fissuring, distal splitting or notching and progressive uniform thinning of nail plate. Onychorrhexis, onychoschizia, brittleness, crumbling or fragmentation of the nail plate and onychomadesis leading to nail shedding may also occur. Pterygium unguis is the hallmark of severe nail disease. Nail abnormalities in lichen planus can also present as longitudinal furrows alternating with portions of normal nail plate that appear as ridges, uniform thinning of the nail plate, pterygium, total nail atrophy, violaceous lines in nail plate and subungual hyperkeratosis.