title: Clustering of pain and its associations with health in people aged 50 years and older: cross-sectional results from the North Staffordshire Osteoarthritis Project.
abstract: OBJECTIVE
  Most pain in patients aged ≥50 years affects multiple sites and yet the predominant mode of presentation is single-site syndromes. The aim of this study was to investigate if pain sites form clusters in this population and if any such clusters are associated with health factors other than pain.
  
  
  METHODS
  Six general practices in North Staffordshire, UK.
  
  
  METHODS
  Cross-sectional, postal questionnaire, study.
  
  
  METHODS
  Community-dwelling adults aged ≥50 years registered at the general practices.
  
  
  METHODS
  Number of pain sites was measured by asking participants to shade sites of pain lasting ≥1 day in the past 4 weeks on a blank body manikin. Health factors measured included anxiety and depression (Hospital and Anxiety Depression Scale), cognitive complaint (Sickness Impact Profile) and sleep. Pain site clustering was investigated using latent class analysis. Association of clusters with health factors, adjusted for age, sex, body mass index and morbidities, was analysed using multinomial regression models.
  
  
  RESULTS
  13 986 participants (adjusted response 70.6%) completed a questionnaire, of whom 12 408 provided complete pain data. Four clusters of participants were identified: (1) low number of pain sites (36.6%), (2) medium number of sites with no back pain (31.5%), (3) medium number of sites with back pain (17.9%) and (4) high number of sites (14.1%). Compared to Cluster 1, other clusters were associated with poor health. The strongest associations (relative risk ratios, 95% CI) were with Cluster 4: depression (per unit change in score) 1.11 (1.08 to 1.14); cognitive complaint 2.60 (2.09 to 3.24); non-restorative sleep 4.60 (3.50 to 6.05).
  
  
  CONCLUSIONS
  These results indicate that in a general population aged ≥50 years, pain forms four clusters shaped by two dimensions-number of pain sites (low, medium, high) and, within the medium cluster, the absence or presence of back pain. The usefulness of primary care treatment approaches based on this simple classification should be investigated.
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: R J
authors.initials: RJ
authors.lastname: Lacey
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK Centre for Statistics in Medicine, University of Oxford, Botnar Research Centre, Oxford, UK.
authors.forename: V Y
authors.initials: VY
authors.lastname: Strauss
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: T
authors.initials: T
authors.lastname: Rathod
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK School of Computing and Mathematics, Keele University, Keele, Staffordshire, UK.
authors.forename: J
authors.initials: J
authors.lastname: Belcher
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: P R
authors.initials: PR
authors.lastname: Croft
authors.affiliation: Department of General Practice, Institute of Health and Society, University of Oslo, Oslo, Norway.
authors.forename: B
authors.initials: B
authors.lastname: Natvig
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: R
authors.initials: R
authors.lastname: Wilkie
authors.affiliation: Arthritis Research UK Primary Care Centre, Research Institute for Primary Care & Health Sciences, Keele University, Keele, Staffordshire, UK.
authors.forename: J
authors.initials: J
authors.lastname: McBeth
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001007:Anxiety; D016000:Cluster Analysis; D003071:Cognition; D003430:Cross-Sectional Studies; D003863:Depression; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010003:Osteoarthritis / Q000150:complications* / Q000523:psychology*; D010146:Pain / Q000453:epidemiology*; D010147:Pain Measurement / Q000379:methods*; D011569:Psychiatric Status Rating Scales; D012890:Sleep; D011795:Surveys and Questionnaires; D006113:United Kingdom
keywords: EPIDEMIOLOGY; PRIMARY CARE; RHEUMATOLOGY