G.P.13.07 Prevalence and diagnosis of sporadic inclusion body myositis (sIBM) in Western Australia.

Abstract

The prevalence of sIBM is known to vary in different populations. Published figures vary from 4.9 x 10-6 to 10.7 x 10-6. A prevalence study in Western Australia (WA) in 2000, found a prevalence of 9.3 X10-6, with an age-adjusted figure of 35.3 X10-6 over 50 years of age. We have undertaken a follow-up survey to determine whether there has been a change in prevalence over the ensuing 6 year period. In addition, a cohort of 57 biopsy-proven sIBM patients has been reviewed to ascertain the average delay in establishing the diagnosis and frequency of misdiagnosis of the condition. All new cases of biopsy-proven sIBM since the previous survey were ascertained from the records of the Neuromuscular Clinic at the ANRI, from hospital pathology departments, and with a questionnaire to all neurologists and rheumatologists. Only patients with definite or probable sIBM were accepted for the survey. Population statistics for the state of WA were obtained from the Australian Bureau of Statistics as at September 2006. The current prevalence figure was found to be 13 X10-6, with an age-adjusted prevalence of 39.5 X10-6 over the age of 50 years, and a male-to-female ratio of 1.4:1. The mean delay from symptom onset to diagnosis was 5.2 years. This was partly accounted for by a delay in seeking medical attention (mean 2.9 years), and by initial misdiagnosis of the condition in 52.7% of patients. The initial diagnoses in this subgroup of patients included arthritis, motor neuron disease, polymyositis and 'old age'. These findings indicate that there has been only a slight increase in prevalence since the previous survey, most likely reflecting improved case ascertainment. However, there is still a considerable delay in the time to diagnosis and a high rate of initial misdiagnosis indicating that the condition is still not well recognised, and that there is a need to increase the level of awareness of sIBM among the medical community.Copyright © 2007