P.189 - Incidence and prevalence of inclusion body myositis in western Sweden

Abstract

The slowly progressive muscle disease inclusion body myositis (IBM) causing muscle weakness and swallowing difficulties is the most common acquired myopathy in the elderly. To obtain more information of comorbidity, biomarkers and genetic background we aimed to investigate epidemiological aspects of IBM in a population based study. The region Västra Götaland in western Sweden includes approximately 1.5 million inhabitants (data from SCB, Statistics Sweden). Nearly all muscle biopsies performed to diagnose muscle disease in the region have since 1985 been analyzed at the Department of Pathology and Genetics at the Sahlgrenska University Hospital, Gothenburg. Patients were identified by screening all muscle histology reports from 1996 to 2016 for diagnosis myositis or myopathy. An additional approach was to identify all patients with diagnosis IBM at the Neuromuscular Centre at Sahlgrenska University Hospital. All patients living in the region Västra Götaland were included if they fulfilled the ENMC research criteria for clinico-pathologically defined IBM from 2011. The date of the first biopsy fulfilling the ENMC criteria was used as date of diagnosis. A total of 84 patients fulfilled the inclusion criteria. The point prevalence of IBM December 31st 2015 was 27 (95% CI 20–37) per million inhabitants. The incidence rate during the 20-year period varied from 0 (95% CI 0–2.5) to 5.4 (95% CI 2.3–10.1) per million inhabitants and year. Both prevalence and incidence are probably underestimated in our study due to exclusion of patients not fulfilling the strict 2011 ENMC criteria for clinico-pathologically defined IBM. Although inclusion criteria may vary in different studies, the prevalence is similar to a previous study from Norway (33 per million) and higher than a study from the Netherlands (4.9 per million) using the ENMC criteria from 2011 and 1997 respectively. Our well-defined patient cohort will be the basis for further epidemiological studies.