title: Incidence and prevalence of idiopathic inflammatory myopathies in South Australia: a 30-year epidemiologic study of histology-proven cases.
abstract: OBJECTIVE
  To describe the epidemiology of biopsy-proven idiopathic inflammatory myopathies (IIM) in South Australia (SA).
  
  
  METHODS
  Cases of IIM were ascertained by review of all muscle biopsy reports from the Neuropathology Laboratory, Hanson Institute (wherein all adult muscle biopsies in SA are reported) from 1980 to 2009. Clinical correlation of these patients by review of medical records was undertaken. SA population denominator numbers were obtained from the Australian Bureau of Statistics.
  
  
  RESULTS
  Three hundred and fifty-two biopsy-proven cases of IIM were identified between 1980 and 2009. The overall annual incidence of IIM appeared to be rising with a mean incidence of eight cases per million population (95% CI: 7.2-8.9). This corresponded with an increasing annual incidence of inclusion body myositis (IBM) (prevalence of 50.5 cases per million population in 2009, 95% CI: 40.2-62.7). A female preponderance was noted in both dermatomyositis (DM) (F : M = 2.75 : 1.00) and polymyositis (PM) (F : M = 1.55 : 1.00) but gender distribution was almost equal in IBM (F : M = 1.1 : 1.0). Mean age at diagnosis for IBM (67.5 years) was higher than for DM (55.1 years) and PM (59.0 years). A higher proportion of DM patients reported living in urban dwellings and DM patients tended to be predominantly professionals.
  
  
  CONCLUSIONS
  In SA there is an increasing incidence of IBM and the prevalence is one of the highest reported to date. This may reflect an increase in the number of biopsies performed, improved histological techniques or a genuine increase in incidence.
authors: Department of Immunology, SA Pathology, Flinders Medical Centre, South Australia, Australia. juann.tan@health.sa.gov.au
authors: Ju Ann
authors: JA
authors: Tan
authors: Peter J
authors: PJ
authors: Roberts-Thomson
authors: Peter
authors: P
authors: Blumbergs
authors: Paul
authors: P
authors: Hakendorf
authors: Sally R
authors: SR
authors: Cox
authors: Vidya
authors: V
authors: Limaye
mesh_terms: D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D016009:Chi-Square Distribution; D005260:Female; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D009132:Muscles / Q000473:pathology*; D009220:Myositis / Q000453:epidemiology* / Q000473:pathology*; D011237:Predictive Value of Tests; D015995:Prevalence; D012307:Risk Factors; D017678:Sex Distribution; D012737:Sex Factors; D012959:Socioeconomic Factors; D013021:South Australia / Q000453:epidemiology; D013997:Time Factors; D055815:Young Adult
keywords: South Australia; dermatomyositis; epidemiology; inclusion body myositis; inflammatory myositis; polymyositis