Comprehensive evaluation of finger flexor tendon entheseal soft tissue and bone changes by ultrasound can differentiate psoriatic arthritis and rheumatoid arthritis.

Objectives: To determine whether a detailed sonographic evaluation of the hand flexor tendon compartment could help differentiate between psoriatic arthritis (PsA) and rheumatoid arthritis (RA).

Methods: Thirty-seven patients with PsA, 47 with RA and 10 healthy controls (HC) had flexor tendon (FT) compartment imaging of the dominant hand 2nd to 4th tendons using grey scale (GS) and power Doppler (PD) ultrasound (US) with evaluation for tenosynovitis, peri-tendinous lesions, soft tissue oedema and bony changes at FT insertions. 24/37 PsA and 19/47 RA cases had morning stiffness and 19/37 PsA and 10/47 RA had swollen and/or tender fingers.

Results: Tenosynovitis was more common in PsA (25/37) despite higher DAS28 scores in RA (25/37 versus 10/45; p<0.001). Peri-tendinous dermal soft tissue oedema with associated PD signal was evident in one third of PsA patients but in no RA patients (p=0.003). Flexor tendon enthesopathy including new bone formation at the insertional site was significantly more common in PsA (p=0.001). Considering a total inflammatory score per patient summing up the three modifications of the flexor tendon (tenosynovitis, peri-tendinous oedema and insertional enthesophytes) the difference between PsA and RA remained statistically significant (p<0.001).

Conclusions: Our study adds to the growing body of literature that high resolution US of the hand FT compartment may help differentiate between RA and PsA, which needs assessment in the diagnostic setting.