A longitudinal study of functional disability in a national cohort of patients with polymyositis/dermatomyositis

Abstract

Objective. To analyze changes in functional status and the factors contributing to disability in a national inception cohort of 257 patients with polymyositis/dermatomyositis (PM/DM). Methods. Data were gathered from patients' self-reports on questionnaires: one concerning disease- and treatment-related complications, and the other concerning disability, as reflected by a disability index (DI) derived from the Health Assessment Questionnaire (HAQ). Results. Based on certain characteristics that differentiated disability patterns, 3 groups of patients were identified. Group 1 patients (n = 153) were ≥60 years old and never had avascular necrosis (AVN) or a vertebral compression fracture (CF), Group 2 patients were >60 and never had AVN or a vertebral CF, and Group 3 patients reported AVN or a vertebral CF irrespective of age. As measured by the HAQ DI, disability increased very gradually over time in Group 1 patients and more rapidly in Group 2 and Group 3 patients. The increase in disability in patients experiencing AVN was greater than that in patients with similar pre-AVN disease characteristics who did not develop AVN (P = 0.003). Conclusion. In this prospective study of disease course and iatrogenic factors related to functional disability in PM/DM, the HAQ DI increased with disease duration. Corticosteroid-related morbidity, as reflected by the development of AVN or CF, significantly contributed to patient-reported functional disability.