Nail and distal interphalangeal joint in psoriatic arthritis

To study distal interphalangeal (DIP) joints in patients with psoriatic arthritis (PsA) with or without onychopathy, using magnetic resonance imaging (MRI).

Twenty-three patients with PsA (9/14 F/M, median age 47 yrs), 12 with onychopathy (2/10 F/M, median age 44 yrs) and 11 without (7/4 F/M, median age 52 yrs), and 10 control subjects (5/5 F/M, median age 43.2 yrs) were enrolled. MRI of nail and distal phalanx (DP) including examination of DIP joints was carried out. MRI was performed with a surface coil in a 1.5 T device. For each selected finger, both longitudinal and axial scans were performed. The involvement of nail, DP, and DIP joint was scored.

Nail thickening with or without surface irregularity occurred in 95.7% of cases (100% with onychopathy and 90.9% without). MRI nail involvement was more frequent in patients with clinical evidence of onychopathy than in those without (p = 0.003). Similarly, 95.7% of patients showed MRI abnormalities of DP (100% with onychopathy and 90.9% without). MRI DP abnormalities were more marked in patients with clinical evidence of onychopathy than in those without (p = 0.009). Involvement of DIP joints was present in 34.8% of cases (58.3% with onychopathy and 9.1% without), and onychopathic patients showed marked MRI DIP joint involvement in 5 cases and mild in 2, while patients without onychopathy showed minimal changes in one case (p = 0.03). Considering the entire group of patients, MRI involvement of DIP joints was always associated with MRI DP changes, and in no case was it present alone.

MRI nail involvement was present in almost all patients with PsA studied, even in those without clinically evident onychopathy. MRI involvement of DP always overlapped with nail involvement, since it was present in all psoriatic cases showing MRI nail involvement. In contrast, MRI DIP joint involvement was almost exclusively in a lower percentage of the patients with clinical nail involvement and was always associated with MRI DP changes. Our results suggest that DIP joint involvement is always secondary to nail and DP involvement.