Background/Purpose:

Clinical joint assessment by the rheumatologist is a key examination of patients with psoriatic arthritis (PSA). A clinically swollen joint is predicting subsequent joint damage. Since joint assessment is regarded time-consuming, a tension exists between comprehensiveness, e.g. using complete joint counts (JC; 76/78 or 66/68), and feasibility.  Reduced JC, such as the 28 joint count, however, may be less valuable in PSA than RA due to differences in joint patterns.

Here, we examined the validity of a reduced 28 swollen and tender JC, using the extended JCas comparators.

Methods:

We analyzed data from a random subset of 80% of patients enrolled in the ADEPT (n=264) and the IMPACT-2 trial (n=163). In ADEPT a 76/78 JC was performed, in IMPACT-2, it was the 66/68 JC only. At week 24 of the two trials, patients with a complete absence of SJC or TJC by the 28-count were analyzed for their residual joint activity. Sensitivity and NPV for each joint count were calculated for each study. Finally, we analyzed the residual tender and swollen joints of 76/78 and 66/68 JC remained active in patients with a 28-joint count of 0 at endpoint.

Results:

As summarized in table 1, investigation of SJC at week 24 in ADEPT showed that 63 of all 264 patients (23.9 %) achieved a SJC28=0; of these 63 patients, 51 (81%) also had a SJC66=0 and 50 (79.4 %) had a SJC76=0. Twelve and 13 patients, respectively, had residual SJC76 or SJC66 while having a SJC28=0. Of the 52 patients with a TJC28=0, 41 and 39, respectively, had also TJC78=0 and TJC68=0, while 11 and 13 patients had residual TJC68 or TJC78.

In IMPACT2, 50 of 163 patients (30.7%) achieved SJC28 remission, with 15 patients (30%) of these remaining active by SJC66. TJC28 remission was achieved by 44 patients, with 17 patients (38.6 %) not achieving complete TJC68 remission.

Exploration of individual residual swollen and tender joints showed mainly foot and ankle joints being active/tender at week 24, as can be seen in figure 1.

Conclusion:

Absence of swelling by the 28 joint count in PsA seems to not adequately reflect the situation of all relevant joints, as in at least one of four patients residual clinical activity is detectable by more comprehensive 76/78 and 66/68 joint counts. Assessment of ankle and foot joints, especially MTPs, contributed numerically most to the missed joints. These limitations should be considered when treating PsA patients to target.

Figure 1: Swollen (red) and tender (blue) joints for all patients at baseline (A+C) and patients JC28=0 at week 24 (B+D).