Diagnosis of nail psoriasis: importance of biopsy and histopathology

Background Involvement of the nail is quite common in psoriasis and at times may be the sole diagnostic clue. However, the histopathology of nail psoriasis has not been adequately evaluated. A confirmation of the diagnosis is required in cases suspected to have nail psoriasis in order to plan long-term therapy. Objectives To assess the diagnostic significance and safety profile of nail biopsy in cases with nail psoriasis. Methods Clinical and mycological features were studied in 42 patients with nail psoriasis. Of these, 22 patients gave consent for nail biopsies to be taken and the histopathological changes were assessed. Results Males were affected more commonly (57%) with a peak incidence in the age group of 10-20 years (29%). Distal onycholysis, discoloration of nail plate, subungual hyperkeratosis and fine nail pitting were the predominant clinical features. In the 22 biopsies done, hyperkeratosis with parakeratosis (91%) was found to be the most common and hypergranulosis was the least common histological finding (36%). Clinicohistological correlation was possible only in 55% cases. Periodic acid-Schiff (PAS) staining was done for all biopsies. Conclusions Histopathological examination of nails is a valuable diagnostic aid, especially in the absence of skin lesions. Examination of the PAS-stained sections is necessary before making a histological diagnosis of nail psoriasis because onychomycosis and psoriasis may show similar histology.