[Nail psoriasis--an ignored disorder. Pathogenesis, diagnosis and therapy]

Approximately 50% of all patients with psoriasis develop characteristic nail changes as a clinical correlate of psoriatic inflammation of the nail matrix and/or nail bed. The most frequent signs of nail psoriasis are pitting and distal onycholysis. The most commonly used score to assess the severity of nail involvement at present is the Nail Psoriasis Severity Index (NAPSI). Although more than half of affected patients experience a significant physical and mental impairment, this index does not include patient-reported symptoms. There is a striking association between nail psoriasis and a higher risk of psoriatic arthritis with a prevalence of nail involvement among patients with psoriatic arthritis as high as 70%. A possible explanation is the close anatomical link between the nail apparatus and the distal interphalangeal joint; enthesitis of the latter is carried by fibers to the nail and becomes clinically visible as nail psoriasis. Nail involvement is not adequately reflected in current concepts of disease management. There is limited evidence for the efficacy of topical therapies in nail psoriasis. A number of large studies document an improvement of nail psoriasis in response to biologics and, more recently, also to methotrexate.