Trajectories of change in symptom severity in patients with fibromyalgia: exploratory analyses of a randomised controlled trial.

The clinical picture of fibromyalgia (FM) symptoms fluctuates, and the symptom severity varies within and between patients. The current study aimed to identify groups of PDS trajectories and to explore differences in baseline characteristics between the potential groups of trajectories. We included patients from a completed randomised controlled trial, in total 170 patients diagnosed with FM according to the ACR 2010 criteria. The mean age was 40 years, and 94% were women. Symptom severity was assessed by the Polysymptomatic distress scale (PDS) [range 0 (no symptoms) to 31] at four timepoints over 13-18 months. Latent class growth analysis was used to identify patient trajectories based on their response pattern on the PDS. Potential differences in baseline characteristics between the trajectories were compared using appropriate statistical tests. Two distinct PDS trajectories were identified with 110 patients (65%) classified as the "no improvement" group and 60 (35%) as the "some improvement" group. Mean PDS scores at pre-baseline were ≥ 20 in both groups. At 12 months, the groups diverged, mean (SD) PDS score was 14 (3.82) in the "some improvement" group and 21 (4.12) in the "no improvement" group. There were no significant differences in baseline characteristics between the groups of PDS trajectories. We identified one group of FM patients that improved slightly during the study period and one group that not improved. There were no differences in baseline characteristics between the two groups.