title: The incidence of fibromyalgia and its associated comorbidities: a population-based retrospective cohort study based on International Classification of Diseases, 9th Revision codes.
abstract: BACKGROUND
  The epidemiology of fibromyalgia is poorly defined. The incidence of fibromyalgia has not been determined using a large population base. Previous studies based on prevalence data demonstrated that females are 7 times more likely to have fibromyalgia than males and that the peak age for females is during the childbearing years.
  
  
  OBJECTIVE
  We have calculated the incidence rate of fibromyalgia in a large, stable population and determined the strength of association between fibromyalgia and 7 comorbid conditions.
  
  
  METHODS
  We conducted a retrospective cohort study of a large, stable health insurance claims database (62,000 nationwide enrollees per year). Claims from 1997 to 2002 were examined using the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) codes to identify fibromyalgia cases (ICD code 729.1) and 7 predetermined comorbid conditions.
  
  
  RESULTS
  A total of 2595 incident cases of fibromyalgia were identified between 1997 and 2002. Age-adjusted incidence rates were 6.88 cases per 1000 person-years for males and 11.28 cases per 1000 person-years for females. Females were 1.64 times (95% confidence interval = 1.59-1.69) more likely than males to have fibromyalgia. Patients with fibromyalgia were 2.14 to 7.05 times more likely to have one or more of the following comorbid conditions: depression, anxiety, headache, irritable bowel syndrome, chronic fatigue syndrome, systemic lupus erythematosus, and rheumatoid arthritis.
  
  
  CONCLUSIONS
  Females are more likely to be diagnosed with fibromyalgia than males, although to a substantially smaller degree than previously reported, and there are strong associations for comorbid conditions that are commonly thought to be associated with fibromyalgia.
authors.affiliation: Department of Family and Preventive Medicine, University of Utah, Salt Lake City, Utah 84108, USA. peter.weir@hsc.utah.edu
authors.forename: Peter T
authors.initials: PT
authors.lastname: Weir
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Harlan
authors.forename: Flo L
authors.initials: FL
authors.lastname: Nkoy
authors.forename: Spencer S
authors.initials: SS
authors.lastname: Jones
authors.forename: Kurt T
authors.initials: KT
authors.lastname: Hegmann
authors.forename: Lisa H
authors.initials: LH
authors.lastname: Gren
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Lyon
mesh_terms: D017677:Age Distribution; D015897:Comorbidity; D005260:Female; D005356:Fibromyalgia / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D008297:Male; D012189:Retrospective Studies; D012737:Sex Factors; D014481:United States / Q000453:epidemiology