<prompt> Least common site involvement in psoriasis is:Scalp involvementNail involvementCNS involvementArthritis  <response>: Ans. c. CNS involvementScalp is a common site of involvement in psoriasis. Corona psoriatica is a band of psoriasis, projecting beyond hairline on forehead.Nail changes in psoriasis are pitting, onycholysis, subungual hyperkeratosis, splinter hemorrhages, uneven surface. 