Long-term follow-up of patients with idiopathic inflammatory myopathy at Waitemata District Health Board.

Background: Idiopathic inflammatory myopathies (IIMs) are an uncommon group of diseases that can be associated with significant morbidity and mortality related to systemic involvement or treatment-related complications.

Aim: This study reports the concomitant diseases, extent of organ involvement, immunosuppressive use, treatment-related complications and damage outcome in a cohort of adult IIM.

Methods: All patients with IIM fulfilling at least 3 of the 4 Bohan and Peter criteria were identified. Medical notes were reviewed retrospectively. Data was collected for clinical presentation, autoantibody profile, immunosuppressives received, treatment-/disease-related complications and mortality rate. Systemic involvement was divided into 12 organ systems. Patient damage index was calculated using the Myositis Damage Index (MDI) tool.

Results: Twenty patients were identified from a single centre, with median duration of follow-up of 9 years. The majority of patients had polymyositis, with the remaining having dermatomyositis. Osteoporosis and osteopenia were the most common concomitant diseases observed, at 111 per 1,000 patient years, followed by lung involvement with 78 events per 1,000 patient years follow-up. ANA was positive in 6/20(30%) patients with Jo-1 positivity in 10% of patients. Nineteen patients (95%) received steroids. There were significant steroid-related complications, with 85% of patients developing osteopenia/osteoporosis. The mean MDI score was 3.11. The mortality rate was 52/1,000 patient years and infection was the most common cause of death.

Conclusion: There is significant treatment-related morbidity in adult IIM, with a high incidence of steroid-related complications, in particular, osteoporosis. Infections accounted for the most common cause of death.