Chabal C, Dunbar PJ, Painter I, et al. Properties of Thermal Analgesia in a Human Chronic Low Back Pain Model. J Pain Res. 2020 Aug 13;13:2083-2092. doi: 10.2147/JPR.S260967. eCollection 2020. (Original study)

Purpose: For years, heat has been used for comfort and analgesia is recommended as a first-line therapy in many clinical guidelines. Yet, there are questions that remain about the actual effectiveness of heat for a condition as common as chronic low back pain, and factors such as time of onset, optimal temperature, and duration of effect.

Materials and Methods: A randomized double-blinded controlled trial was designed to compare the analgesic response to heat delivered via pulses at 45°C (experimental group, N=49) to steady heat at 37°C (control group, N=51) in subjects with longstanding low back pain. Treatment lasted 30 minutes with follow-up out to four hours. The hypothesis was that the experimental group would experience a higher degree of analgesia compared to the control group. Time of onset and duration of effect were also measured.

Results: Both groups were similar in average duration of pain (10.3 years). The primary outcome measure was pain reduction at 30 minutes after the end of treatment, using a 10-points numeric pain scale. Reduction in pain was greater for the experimental group than the control group (difference in mean reduction = 0.72, 95% CI 0.15-1.29, p = 0.014). Statistically significant differences in pain levels were observed from the first measure at 5 minutes of treatment through 120 minutes after completion of treatment. Reduction in pain associated movement was greater in the active heat group than the placebo group (p = 0.04).

Conclusion: High-level pulsed heat (45°C) produced significantly more analgesia as compared to steady heat at 37°C at the primary end point and for an additional 2 hours after treatment. The onset of analgesia was rapid, <5 minutes of treatment. The results of this trial provide insight into the mechanisms and properties of thermal analgesia that are not well understood in a chronic low back pain model.

Discipline Area Score
Physician 5 / 7
Rehab Clinician (OT/PT) 5 / 7
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Rehab Clinician (OT/PT) rater

Interesting project. It's not surprising that heat results in decreased pain as that has been known for years. It seems a two hour benefit is not clinically meaningful. What it does offer is a window of less pain that can be used to do additional interventions. It could be useful, clinically, with this in mind.
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