Objectives: To assess the long-term prognosis of dermatomyositis and pol myositis.
Methods: 69 patients with dermatomyositis or polymyositis were selected according to the diagnostic criteria of Bohan and Peter and were followed up for a minimum of 6.3 years (for surviving patients) (mean 11.6 years). Clinical and biological features, and pulmonary and muscle parameters were considered as prognostic factors for death. Functional disability was assessed using a 4-stage grading system.
Results: 30 deaths (43.5%) occurred mainly due to cardiovascular (8), pulmonary (8), carcinomatous (5) and iatrogenic complications (5). Survival rates were 82.6% at 1 year, 73.9% at 2.66, 7% at 5 and 55.4% at 9. Significant prognostic factors for death (Cox model with time-dependent covariates) were old age (p < 0.0001), dysphonia (p < 0.001), pulmonary interstitial fibrosis (p < 0.02), absence of dysphagia (p < 0.02) and asthenia-anorexia (p < 0.05). Dermatomyositis and polymyositis subgroups had slightly different significant prognostic factors for death: old age, cancer, pulmonary interstitial fibrosis and asthenia-anorexia for dermatomyositis; old age, failure to improve muscle strength in response to treatment after one month, and the absence of myalgia as presenting symptom for polymyositis. At the end of the follow-up, 33/39 surviving patients (84.6%) had no or insignificant muscular disability, whereas 3 children were bedridden due to generalized calcinosis.
Conclusions: High mortality occurred in the first year, and the survival rate decreased continually up to 9 years. The main prognostic factor for death is old age, but dermatomyositis and polymyositis must be considered separately. General features (pulmonary fibrosis, cancer, asthenia-anorexia) are involved in dermatomyositis, whereas muscular symptoms are the most significant in polymyositis. The long-term functional prognosis was fairly good, except for generalized calcinosis, which tended to occur in childhood dermatomyositis.