Assessment of nail unit structures by ultrasound in patients with psoriatic arthritis and their correlations with disease activity indices: a case-control study.

Ultrasound (USG) of nail was performed to assess, (1) morphological alterations of nail plates in psoriatic arthritis (PsA) patients, (2) differences of nail unit parameters [nail bed thickness (NBT), nail matrix thickness (NMT) and nail plate distance (NPD)] in PsA patients from healthy controls (3) correlation of nail unit parameters with PsA disease activity indices. Total of 895 fingernails (448 nails of 45 PsA patients and 447 of 45 controls) were evaluated by USG. Psoriasis Area and Severity Index (PASI), Disease Activity in Psoriatic Arthritis (DAPSA), and Nail Psoriasis Severity Index (NAPSI) were calculated in PsA patients. Nail unit parameters were compared between two study groups. Correlation study was done between nail unit parameters and disease activity indices. All PsA patients showed ultrasound evidence of nail plate changes (87.95% of the total fingernails and 75.34% of the clinically normal nails). Loosening of the ventral nail plate border was most common (51.79%). Mean NBT (PsA: 0.19 ± 0.035 cm, control: 0.17 ± 0.018 cm, p = 0.003) and mean NMT (PsA: 0.32 ± 0.041 cm, control: 0.28 ± 0.031 cm, p = < 0.0001) were significantly increased in the PsA patients. Moderately positive correlation was observed between NAPSI score and mean NMT (Spearman r = 0.411, 95% confidence interval: 0.125-0.634, p = 0.005). USG evidence of nail plate alterations was frequent among PsA patients, even in clinically normal nails. Increased mean nail bed and matrix thickness were noted in PsA patients. Mean NMT had a moderately positive correlation with NAPSI score.