Evaluation of nail disease in psoriatic arthritis by using a modified nail psoriasis severity score index

Background The Classification of Psoriatic Arthritis Study Group published new criteria for classifying psoriatic arthritis (PsA) which included nail psoriasis. Our aim was to clarify the clinical importance of nail disease in PsA patients. Methods We investigated the types and severity of nail disease by using the modified nail psoriasis severity score index (mNAPSI) in 23 PsA patients and 23 patients with uncomplicated psoriasis. We analyzed the relationships of mNAPSI with nail fold psoriasis, psoriasis area and severity index score, swollen and/or tender joint counts, distal interphalangeal (DIP) joint disease, acute phase reactants and the score on the Japanese version of the standard health assessment questionnaire. Results The mNAPSI in 23 PsA patients was higher than that of controls (4.8 +/- 5.3 vs. 2.3 +/- 3.7, P < 0.05). The severity of fingernail disease in PsA patients was significantly associated with DIP joint disease (8.6 +/- 5.9 vs. 3.1 +/- 3.3, P < 0.05) and nail fold psoriasis (6.7 +/- 5.2 vs. 3.5 +/- 5.2, P < 0.05). There were no correlations between the mNAPSI and other systemic involvements. Conclusions The nail involvement and prolonged nail bed psoriasis were common in PsA patients. Nail fold psoriasis and DIP joint arthritis were associated with nail involvement in PsA patients. Nail psoriasis would be related to the Koebner phenomenon and local inflammatory DIP joint arthritis in PsA patients, and we suggested that nail involvement in PsA was among the disorders indicative of distal phalanx enthesitis.