Pain is common in myositis and associated with disease activity

Understanding pain in myositis remains challenging. This study aimed to assess patient-reported pain and its correlation with myositis core set measures (CSMs), patient-reported outcomes (PROs) and functional measures.

Fifty subjects underwent baseline, 3-month and 6-month assessments, evaluating myositis CSMs, functional measures and PROs. Pain was measured using three methods: (i) a 10-cm visual analogue scale, (ii) the pain score from the HAQ Disability Index and (iii) the Short Form 36 survey pain questions. Correlations between disease activity measures and pain were examined at baseline, and changes in both were assessed at 6 months, along with longitudinal change of pain. The change in pain was also correlated with the published 2016 ACR/EULAR myositis response criteria, physician/patient's assessment of change.

Nearly half of patients (45%) reported moderate to severe pain in all three pain scales, with higher severity of pain in PM/necrotizing myopathy subset. At baseline, pain severity showed a strong correlation with most CSMs, PROs and functional outcomes in all three pain scales, and similar trends were noted for change in pain at the 6 months. On longitudinal analysis, the physical function scores and fatigue showed strong correlation with pain. Pain improved in myositis patients with improvement in disease activity over time.

Pain is common in myositis and is associated with multiple measures of disease activity, PROs and functional outcomes in myositis. Most importantly pain improves with improvement in disease activity. SF-36 pain questions have good psychometric properties.