HOTFy: randomised clinical trial for hyperbaric oxygen therapy in fibromyalgia

Fibromyalgia is a polysymptomatic central sensitisation disorder characterised by widespread pain, fatigue, sleep disturbances and neuropsychiatric features. Hyperbaric oxygen therapy modulates neuroinflammation, mitochondrial function and neuroplasticity, thereby yielding analgesic and functional benefits.

Evaluate the efficacy and optimal timing of hyperbaric oxygen therapy as an adjunct to standard care for fibromyalgia.

This single-centre, randomised, cross-over group, assessor-blinded clinical trial was conducted in the Department of Rheumatology at the University Hospital of the Federal University of Juiz de Fora, Juiz de Fora, Brazil, and adhered to Consolidated Standards of Reporting Trials (CONSORT) guidelines. Women (18-70 years) with a diagnosis of fibromyalgia for ≥2 years were randomised 1:1 to early hyperbaric oxygen therapy plus standard care or standard care alone (delayed group). Intention-to-treat (ITT) analysis was conducted with all 56 participants (mean age: 51.0±9.8 years; mean body mass index: 30.5±5.1 kg/m²).

Standardised care (education, exercise and pharmacotherapy) plus hyperbaric oxygen therapy was delivered at 2.3 atmospheres absolute for 90 min, five times per week, over 8 weeks (total 32-40 sessions). The early group received hyperbaric oxygen therapy during weeks 0-8, while the delayed group received it during weeks 8-16, following the same protocol.

Primary endpoints included the Fibromyalgia Impact Questionnaire-Brazilian Portuguese (FIQR-Br), the pain visual analogue scale (VAS) and the Symptoms Assessment Scale-40 (EAS-40) for psychopathology. Secondary endpoints included the 12-Item Short-Form Health Survey (SF-12) physical and mental components and adverse effects. Assessments were conducted at baseline, 8 weeks and 16 weeks, and analysed using a mixed-design 2×3 analysis of variance (group: early vs delayed; time: baseline, 8 weeks and 16 weeks) with Greenhouse-Geisser corrections as needed, followed by Bonferroni post hoc tests. Missing data were assessed using Little's missing completely at random (MCAR), and considering the ITT analysis, the means imputed for missing data were estimated through expectation maximisation. Effect sizes were reported as partial η² and Cohen's d with α=0.05.

44 participants completed the study, and the overall withdrawal rate was 21.4% with no baseline between-group differences. Significant time effects were observed for all primary outcomes and the SF-12 outcome (p<0.001; η²=0.23-0.60). Group×time interactions were significant for FIQR-Br, VAS, EAS-40 and SF-12 physical and mental (p≤0.02; interaction η² up to 0.23), indicating improvements during active hyperbaric oxygen therapy exposure. Compared with standard care alone over 8 weeks, combined treatment achieved greater gains: FIQR-Br, -31.1% vs -14.4%; VAS, -54.0% vs -33.5%; EAS-40, -28.4% vs -3.7%; SF-12 physical, +39.1% vs +14.8%; SF-12 mental, +57.4% vs +31.9%. Large within-group effect sizes were observed (eg, VAS d=2.5-2.7; FIQR-Br d=1.4-1.7). Efficacy was equivalent regardless of time started, and the benefits converged by the end of each hyperbaric oxygen therapy phase. After stopping hyperbaric oxygen therapy, the FIQR-Br and SF-12 mental component scores regressed towards standard care levels, whereas residual improvements persisted for up to 8 weeks in VAS, EAS-40 and SF-12 physical component scores. Adverse events were infrequent; one case of otalgia required extended management. Withdrawals were primarily due to non-compliance or intolerance to chamber confinement. No serious or unexpected safety concerns were reported.

Hyperbaric oxygen therapy, delivered under a standardised protocol, is an effective and well-tolerated adjunct to multimodal fibromyalgia care. Timing can be individualised: early initiation for rapid relief or stepped introduction after optimised usual care, with comparable overall efficacy. The durability of the benefit appears to be exposure dependent, and maintenance or booster schedules merit further evaluation.

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