Patients with psoriatic arthritis who met the CASPAR criteria and were 18-70 years old were included. Participants with infection of the nails to be examined, loss of nails, trauma history of the nails, having the habit of nail biting, peripheral neuropathy, peripheral vascular disease, another rheumatological disease, systemic infection, and pregnancy were excluded.

A gender- and age-matched healthy controls were included. They were recruited from the healthy relatives of the hospital staff. Participants with infection of the nails to be examined, loss of nails, trauma history of the nails, having the habit of nail biting, peripheral neuropathy, peripheral vascular disease, any rheumatological disease, systemic infection, and pregnancy were excluded.

The MyLab 60 (Esaote Biomedica Genoa, Italy) device and linear probe were used. Nails were examined in B-mode grayscale and power Doppler.

The sonographic normal nail plate term indicates a trilaminar band of the nail plate with two hyperechoic layers separated by a hypoechoic one. The "nail plate impairment score" means the number of nails with impaired trilaminar band (plate) among the 12 nails (all hand nails and toenails). The score ranges between 0-12, with 0 indicating no plate impairments (better) and 12 reflecting the maximal prevalence of impairment (worse).

The plate thickness of each nail was measured (in millimeters) by greyscale USG, then, the sum of 12 nails evaluated (all hand nails and toenails) was calculated as "nail plate thickness score" for a participant (in millimeters). Higher scores were expected to mean worse outcome.

The sonographic nail bed is the dark area below the nail plate to the cortical bone. The nail bed thickness of each nail was measured (in millimeters) by greyscale USG, then, the sum of 12 nails evaluated (all hand nails and toenails) was calculated as "nail bed thickness score" (in millimeters) for a participant. Higher scores were expected to mean worse outcome.

The total nail thickness (including the plate and bed) of each nail was measured (in millimeters) by greyscale USG, then, the sum of 12 nails evaluated (all hand nails and toenails) was calculated as "nail thickness score" (in millimeters) for a participant. Higher scores were expected to mean worse outcome.

Doppler activity of the nail bed and matrix was measured by power Doppler USG. The power Doppler signal for each nail was graded from 0 to 3: 1 point for a signal in less than 25 percent of the nail bed area, 2 points for a signal 25 to 50 percent, 3 points for a confluent signal in more than 50 percent of the nail bed area, and 0 point for no signal. Then, the sum of 12 nails evaluated (all hand nails and toenails) was calculated as "Doppler activity score". The score ranges between 0-36, with 0 indicating no activity (better) and 36 reflecting the maximal activity (worse).

Patients with PsA were evaluated twice in order to assess interobserver reliability. For this purpose, another investigator experienced in musculoskeletal USG performed the ultrasonographic evaluations with the same device but separately from the one who made the first assessment. Then, the consistency between the observers was calculated for each scoring by intraclass correlation coefficient (range 0-1).

"Minimal Disease Activity" is used for remission criteria in patients with PsA. It is defined as 5 out of 7 of the following criteria: tender joint count ≤1, swollen joint count ≤1, PASI ≤1, patient pain visual analog score (VAS) ≤15 mm, patient global disease activity VAS ≤20 mm, health assessment questionnaire ≤0.5, and tender entheseal points ≤1