Leukonychia striata
Leukonychia striata, transverse leukonychia, or Mees lines are a whitening or discoloration of the nail in bands or "stria" that run parallel the lunula (nail base). This is commonly caused by physical injury or disruption of the nail matrix. Common examples include excessive biting or tapping of the nails, trauma or injury from accidents involving doors or windows, and extensive use of manicure. It may also occur in great toenails as a result of trauma from footwear. Alternatively, the condition can be caused by heavy metal poisoning, most commonly by lead. Finally, it can be caused by cirrhosis of the liver or chemotherapy. The tendency toward leukonychia striata is sometimes inherited in an autosomal dominant fashion. In other cases, it can be attributed to vigorous manicuring and trauma aforementioned, or to a wide variety of systemic illnesses. Serious infections known for high fevers, measles, malaria, herpes, and leprosy may also cause this condition. In many patients, there is no obvious cause, and the streaks resolve spontaneously. There is a similar condition called Muehrckes lines (apparent leukonychia) which differs from leukonychia in that the lines fade with digital compression and does not migrate with the growth of the nail. Leukonychia punctata
Also known as "true" leukonychia, this is the most common form of leukonychia, in which small white spots appear on the nails. Picking and biting of the nails are a prominent cause in young children and nail biters. Besides parakeratosis, air that is trapped between the cells may also cause this appearance.
Schönlein associated the purpura and arthritis, and Henoch the purpura and gastrointestinal involvement. The English physician William Heberden (1710–1801) and the dermatologist Robert Willan (1757–1812) had already described the disease in 1802 and 1808, respectively, but the name Heberden–Willan disease has fallen into disuse. William Osler was the first to recognise the underlying allergic mechanism of HSP. See also
Cutaneous small-vessel vasculitis

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