Objective: To determine the reliability of self reported joint counts to assess pain or swelling in ankylosing spondylitis (AS).
Methods: 217 outpatients fulfilling the modified New York criteria for AS were asked to mark painful joints and swollen joints on two mannequins presenting 44 and 40 joints respectively. A doctor or research nurse assessed the same joints for pain and swelling on the same day, after completion by the patient, without information on the results of the patient's assessment.
Results: Forty six (21%) patients reported one or more swollen joints (mean number of swollen joints 0.5, range 0-8); the doctor found one or more swollen joints in 54 (25%) of the patients (mean number of swollen joints 0.8, range 0-31). The overall agreement on the number of swollen joints between patients and doctor was moderate (intraclass correlation coefficient (ICC) 0.53). Agreement on individual swollen joints was poor to moderate (kappa 0.1-0.64). 128 (60%) patients reported tender joints (mean number of joints 2.4, range 0-26). The doctors reported one of more tender joints in 50% of the patients (mean number of tender joints 2.2, range 0-34). The overall agreement was also moderate (ICC 0.71). The agreement on individual tender joints was again poor to moderate (kappa 0.19-0.43). There was only high concordance between doctors and patients on the absence of swollen joints (82%). The concordance on the presence of monoarthritis, oligoarthritis, or polyarthritis was low (17-22%).
Conclusion: Owing to these discrepancies in assessment of individual joints and total number of affected joints, joint counts in AS assessed by doctors cannot be replaced by joint counts reported by the patients. Patients are only able to judge if their joints are not swollen.