Psoriatic nail involvement and its relationship with distal interphalangeal joint disease

Psoriatic nail disease and distal interphalangeal (DIP) arthritis both are common manifestations of psoriatic arthritis (PsA). Several clinical characteristics are allegedly associated with DIP joint damage, particularly nail psoriasis. However, there is little evidence to substantiate this phenomenon. The purpose of this study is to investigate the relationship between DIP involvement, nail psoriasis and other parameters. A cross-sectional study involved 45 patients from local rheumatology clinic. Four hundred fifty psoriatic fingernails scored, and the radiographs of all these fingers were reviewed to define PsA DIP arthritic changes. 64.4 % patients had nail psoriasis and 35.6 % had DIP arthritis. Univariate analysis identified that swollen joint-count, digits with chronic dactylitis, HLA-B27 status and nail psoriasis were associated with DIP arthritis. Regression model supported that nail disease was the most significant associated factor of DIP arthritis (OR 9.7, p = 0.05). Nail psoriasis was identified in 40.2 % of digits. Pitting (29.6 %), onycholysis (15.1 %), crumbling (8.2 %), nail bed hyperkeratosis (2.0 %) were noted with the mean modified Nail Psoriasis Severity Index of 0.95 +/-1.68. Among all digits, 57 had DIP arthritis while 393 did not. Within DIP joints with PsA radiological change, 59.6 % had nail disease. Chi-square test with the Bonferroni correction further supported an association between nail psoriasis and DIP involvement with p value of 0.001. Two specific nail subtypes-crumbling and onycholysis-were found to be significantly associated with DIP disease. A significant proportion of PsA patients had nail involvement and DIP arthritis. PsA patients with nail changes may be more susceptible to DIP disease.