Background/Purpose: Hand osteoarthritis (OA) research is in need of disease-specific validated instruments to measure patient-reported outcomes. Self-reported painful joint count (PJC) could be useful to assess pain, including information about the distribution of tender joints, while being less time-consuming than assessor-reported PJC. We investigated metric properties of self-reported PJC compared to assessor-reported PJC to measure pain.

Methods: Symptomatic hand OA patients from the Hand OSTeoArthritis in Secondary care (HOSTAS) study marked which joints were painful on standardized hand diagrams. Pain upon palpation was scored on similar diagrams by trained nurses, who were unaware of patients’ scores. Self- and assessor-reported PJCs were calculated as the sum of painful joints of both hands (range 0-30). Patients also rated pain on visual analogue scale and completed Australian/Canadian Hand Osteoarthritis index pain subscale, Short Form-36 Mental/Physical Component Summary scales, and Hospital Anxiety and Depression Scale. Radiographs were scored according to Kellgren-Lawrence. MRIs of the right distal and proximal interphalangeal joints (DIPs/PIPs) were evaluated for bone marrow lesions and synovitis. Validity was investigated by assessing correlations between self- and assessor-reported PJC, and of both PJCs with other outcome measures. Absolute agreement between PJCs on joint level, and patient level intra-class correlation coefficients (ICCs) were calculated.

Results: Of 524 hand OA patients (86% women, mean age 61, 90% fulfilling ACR criteria), 506 (96.9%) reported ³1 painful joint (median PJC 8 [interquartile range (IQR) 4-13]), while nurses reported ³1 painful joint in 426 (81.3%) patients (PJC 3 [1-7]). Patients and assessors both reported pain most often in DIP 2-3, PIP 2-3 and the thumb base, and least often in metacarpophalangeal joints (MCPs) 2-5. Correlation between self- and assessor-reported PJC was 0.38. Correlations of both PJCs with other measures were comparable, ranging from 0.11 to 0.37 (Table). Absolute agreement was highest in MCPs 2-5 and lowest for thumb base, DIP 2-3 and PIP 2-3 (range 61%-89%). ICC between PJCs was 0.28 (95% confidence interval 0.08-0.14).

Conclusion: Hand OA patients reported more painful joints than assessors. Self-reported PJC correlated weakly with assessor-reported PJC, and other instruments measuring pain and physical health. Divergent correlations with mental health and imaging scores were even lower. Agreement between patients and assessors was highest in joints with low prevalence of pain, but overall agreement was low. Despite apparent advantages, these results suggest that self-reported and assessor-reported PJCs cannot be used interchangeably, and further study of PJC as an outcome measure in hand OA is warranted.