Background: In order to define the onset of a new episode of low back pain (LBP), the definition of a "non-episode" must be clear. De Vet et al reviewed the scientific literature but found no evidence-based definitions of episodes or non-episodes of LBP. However, they suggested that pain-based episodes should be preceded and followed by a period of at least one month without LBP. As LBP is an episodic disease, it is not clear whether a sufficient number of patients with LBP will be LBP-free for at least one month ("non-episode") to justify the use of this duration in the definition of pain free episode.
Objectives: Two clinical populations were followed weekly over one year making it possible 1) to determine the maximum numbers in a row of weeks without LBP, 2) to determine the prevalence of non-episodes throughout a one-year period, and 3) to find the prevalence of patients who reported to be in a non-episode of LBP at the end of the study.
Methods: Secondary data were used from two recent clinical studies, in which weekly automated text messages (SMSes) had been collected on the number of days with LBP in the preceding week for one year. Weeks with 0 days of LBP were defined as "zero-weeks" and four zero-weeks in a row were defined as a period without LBP (a"non-episode") according to de Vet et al's suggestion. The study participants, all from the secondary care sector, consisted of: study 1) patients with LBP and Magnetic Resonance Imaging-identified Modic changes and study 2) patients without obvious acute disc problems, Modic changes or other pathologies, who therefore were assumed to have non-specific LBP. Both studies were two-armed intervention studies without a significant difference in outcome between intervention groups. The number of zero-weeks was identified in each participant. Thereafter the numbers of participants who reported at least one non-episode during the study period were identified. Finally, the numbers of participants who had a non-episode at the end of the study were counted. Estimates are reported with their 95% confidence intervals.
Results: The numbers of participants included in the analyses were 80 and 209. Most commonly, no zero weeks were reported, by 65% (95% CI:55-75) and 56% (95% CI:49-63) of patients, respectively. The percentages of study participants with at least one non-episode at some time during the course of the study were 20% (95% CI:11-29) and 18% (95% CI: 15-21). The percentages of participants who were identified as being in a non-episode at the time of the last week of the study were 5% (95% CI: 0-10) and 4% (95% CI: 1-7) respectively.
Conclusions: The vast majority of these secondary care sector patients had a profile of more or less constant LBP. The estimates for non-episodes during the study period and at the end of the study were very similar for participants with LBP who also had Modic changes and those with non-specific LBP. It is possible that a definition of pain-free periods is pointless in patients seeking care in the secondary care sector.
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