title: Heterogeneity within the fibromyalgia population: theoretical implications of variable tender point severity ratings.
abstract: OBJECTIVE
  The American College of Rheumatology (ACR) tender point (TP) criterion is used in diagnosing fibromyalgia syndrome (FM). There has been little research investigating patterns of positive TP. We investigated response patterns of TP in a sample of patients with FM.
  
  
  METHODS
  Manual TP survey data were available on 1433 patients with FM. Factor analysis was conducted on ACR TP and control (CON) points. Factor scores were cluster analyzed to identify subgroups based on TP scores. Subgroups were compared on demographic and psychosocial variables.
  
  
  RESULTS
  Factor analysis resulted in 4 TP groupings: neck/shoulder girdle, gluteal/trochanteric, and upper extremity regions, and a set of CON TP. Cluster analysis revealed 3 clusters. Group 1 was high on all 3 TP regions and the CON set; Group 2 moderate on the 3 TP regions, low on the CON set; and Group 3 was relatively low on all 3 TP regions and the CON set. The group highest on the CON and TP regions reported the greatest pain (7.58 +/- 1.23; p < 0.001), sleep disturbance (7.05 +/- 1.61; p < 0.001), anxiety (10.14 +/- 4.57; p < 0.001), and depression (8.42 +/- 4.4; p < 0.001).
  
  
  CONCLUSIONS
  TP severity ratings varied among cluster groups, suggesting patients with FM are not homogeneous. Variations in TP severity provide information regarding the degree to which FM affects patients' quality of life. Patients with elevated scores on the CON TP demonstrated a general pattern reflecting lower thresholds for symptom reporting and, perhaps, disease severity. Research is needed to elucidate mechanisms underlying heterogeneity among the FM population.
authors.affiliation: Department of Anesthesiology and Pain Medicine, University of Washington, Seattle, Washington 98195, USA.
authors.forename: Hilary D
authors.initials: HD
authors.lastname: Wilson
authors.forename: Terence W
authors.initials: TW
authors.lastname: Starz
authors.forename: James P
authors.initials: JP
authors.lastname: Robinson
authors.forename: Dennis C
authors.initials: DC
authors.lastname: Turk
mesh_terms: D000328:Adult; D016000:Cluster Analysis; D004311:Double-Blind Method; D005260:Female; D005356:Fibromyalgia / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D008875:Middle Aged; D015337:Multicenter Studies as Topic; D010147:Pain Measurement; D010919:Placebos; D016032:Randomized Controlled Trials as Topic; D012720:Severity of Illness Index; D011795:Surveys and Questionnaires
chemical_list: D010919:Placebos