Contribution of assessing forefoot joints in early rheumatoid arthritis patients: insights from item response theory.
OBJECTIVE
To evaluate the contribution of assessing forefoot joints to the measurement range and measurement precision of joint counts in early rheumatoid arthritis (RA) using item response theory.


METHODS
Baseline measures of tender and swollen joint counts were analyzed in 459 early RA patients from the Dutch Rheumatoid Arthritis Monitoring remission induction cohort. The contribution of forefoot joints was studied by evaluating their effect on the measurement range and measurement precision of measures based on 28-joint counts. In addition, the alignment between the patient and joint distributions was investigated to determine whether the forefoot joints were informative for measuring joint tenderness or swelling of an early RA patient.


RESULTS
In total, 233 patients (50.76%) experienced tenderness and 200 patients (43.57%) experienced swelling in ≥1 forefoot joint. Forefoot joints were more informative for measuring joint tenderness than joint swelling, but did not significantly improve the measurement range and measurement precision of the 28-joint counts. Furthermore, including forefoot joints did not remove the existing discrepancy between the joint and patient distributions in both joint counts.


CONCLUSIONS
Forefoot joints were frequently affected on an individual level, but did not significantly improve the measurement range or precision of 28-joint counts in patients with early RA. From a measurement perspective, reduced joint counts are appropriate for use on a population level. The contribution of assessing forefoot joints on an individual level requires further investigation. Additionally, the results should be cross-validated in patients with longer disease durations to determine whether the pattern of joint involvement is similar in later stages of RA.
Department of Psychology, Health & Technology, Faculty of Behavioural Sciences, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands. L.siemons@utwente.nl
Liseth
L
Siemons
Peter M
PM
Ten Klooster
Erik
E
Taal
Ina H
IH
Kuper
Piet L C M
PL
van Riel
Cees A W
CA
Glas
Mart A F J
MA
van de Laar
D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000175:diagnosis* / Q000503:physiopathology; D015331:Cohort Studies; D005260:Female; D033023:Foot Joints / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index