'Twenty-nail syndrome' is seen in

Nail involvement occurs in 10% of individuals with disseminated lichen planus, and nail lesions may be the only manifestation and can destroy the nails. One, several, or all 20 nails may be involved ("twenty-nail syndrome," where there is loss of all 20 nails without any other evidence of lichen planus elsewhere on the body Twenty-nail dystrophy is a condition that affects the nails of the fingers and toes. This condition most commonly occurs in childhood, but it can occur at any age. Ref: Harrison 20th edition pg 1223