title: Fluctuations in patient reported disease activity, pain and global being in patients with ankylosing spondylitis.
abstract: OBJECTIVE
  To evaluate in patients with AS (i) the fluctuation in self-reported disease activity (BASDAI), patient global well-being [visual analogue scale (VAS)-global] and spinal pain (VAS-pain) during 2 years of follow-up on a group level and (ii) the clinical relevance of these fluctuations on a patient level.
  
  
  METHODS
  Dutch patients from the Outcome in AS International Study cohort completed patient-reported outcome measures every 2 months over 2 years. On the group level, mixed linear models were used to analyse whether the outcome measures were constant over time. On a patient level, relevant changes in scores were assessed by the frequency in which changes would exceed predefined cut-off values (>1.0 or >2.0 on a 0-10 scale) during the 2 years of follow-up using 2-, 4-, 6-, 12- or 24-month assessments.
  
  
  RESULTS
  Ninety patients [median age 47.3 years (sd 11.4), 67.8% male, symptom duration 25.2 years (sd 11.3)] were included. On the group level, the outcome measures remained constant over time. However, large fluctuations were found on the patient level. For example, using 2 month intervals, 92% and 69% of the patients had at least one change of > 1.0 or > 2.0, respectively, in the BASDAI during the 2 year follow-up. When prolonging the interval, the proportion of changes exceeding the cut-off decreased, indicating that information is lost. Similar results were found for the VAS-global and VAS-pain.
  
  
  CONCLUSIONS
  Substantial fluctuations in BASDAI, VAS-global and VAS-pain were found in individuals over time. With longer intervals, fewer fluctuations were observed, indicating that relevant changes might be missed.
authors: Department of Rheumatology, Maastricht University Medical Center, Maastricht ivette.essers@maastrichtuniversity.nl.|School for Public Health and Primary Care, University of Maastricht, Maastricht.
authors: Ivette
authors: I
authors: Essers
authors: Department of Rheumatology, Maastricht University Medical Center, Maastricht.|School for Public Health and Primary Care, University of Maastricht, Maastricht.
authors: Annelies
authors: A
authors: Boonen
authors: Department of Rheumatology, Maastricht University Medical Center, Maastricht.
authors: Matthias
authors: M
authors: Busch
authors: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors: Désirée
authors: D
authors: van der Heijde
authors: Department of Medical Informatics, Uniklinik RWTH Aachen, Aachen, Germany.
authors: Andras P
authors: AP
authors: Keszei
authors: Department of Clinical Immunology and Rheumatology, Academic Medical Center/University of Amsterdam, Amsterdam.|Department of Rheumatology, Atrium Medical Center, Heerlen, The Netherlands.
authors: Robert
authors: R
authors: Landewé
authors: Department of Rheumatology, Leiden University Medical Center, Leiden, The Netherlands.
authors: Sofia
authors: S
authors: Ramiro
authors: Department of Rheumatology, Maastricht University Medical Center, Maastricht.|School for Public Health and Primary Care, University of Maastricht, Maastricht.
authors: Astrid
authors: A
authors: van Tubergen
mesh_terms: D005260:Female; D005500:Follow-Up Studies; D006304:Health Status; D006801:Humans; D008297:Male; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D010146:Pain / Q000453:epidemiology / Q000209:etiology*; D010147:Pain Measurement; D057566:Self Report; D013167:Spondylitis, Ankylosing / Q000150:complications* / Q000453:epidemiology / Q000628:therapy
keywords: ankylosing spondylitis; disease activity; outcome measures