US and dermoscopic features of the 3 groups. Values are n (%) unless otherwise specified.
| Variables | RA−, n = 17 | RA+, n = 25 | PsA, n = 25 | p, RA− vs PsA | p, RA+ vs PsA |
|---|---|---|---|---|---|
| US | |||||
| PTI pattern at MCP joint | 0 (0) | 2 (8.0) | 9 (36.0) | 0.006 | 0.037 |
| CSE pattern at PIP joint | 0 (0) | 0 (0) | 5 (20.0) | 0.069 | 0.050 |
| STE-FT of the digit | 2 (11.7) | 2 (8.0) | 10 (40.0) | 0.080 | 0.018 |
| Erosions, MCP, or PIP | 2 (11.7) | 8 (32.0) | 3 (12.0) | 1.00 | 0.17 |
| At least 1 US feature specific for PsA (PTI or CSE or STE-FT) per patient | 2 (11.7) | 3 (12.0) | 17 (68.0) | < 0.001 | < 0.001 |
| Dermoscopy | |||||
| Sparse or diffuse dotted vessels of proximal nailfold | 4 (23.5) | 3 (12.0) | 24 (96.0) | < 0.001 | < 0.001 |
Significant data are in bold face. US: ultrasonography; RA: rheumatoid arthritis; RA−: seronegative RA; RA+: seropositive RA; PsA: psoriatic arthritis; PTI: peritendon inflammation of the extensor digitorum tendon; MCP: metacarpophalangeal; CSE: central slip enthesitis; PIP: proximal interphalangeal; STE-FT: soft tissue edema around flexor tendon.