Co-occurrence of severe fatigue and insomnia: implications for the outcome of cognitive behavioural therapies

Cognitive behavioural therapy for fatigue (CBT-F) and insomnia (CBT-I) are effective therapies. Little is known on their effectiveness when severe fatigue and insomnia co-occur.

This observational study investigated whether the co-occurrence of fatigue and insomnia influences the outcomes of CBT-F and CBT-I. Furthermore, it was determined if changes in fatigue and insomnia symptoms are associated, and how often the co-occurring symptom persists after CBT.

Patients with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS, n = 241) received CBT-F and patients with insomnia disorder (n = 162) received CBT-I. Outcomes were fatigue severity assessed with the subscale of the Checklist Individual Strength (CIS-fat) and insomnia severity assessed with the Insomnia Severity Index (ISI). In each cohort, treatment outcomes of the subgroups with and without co-occurring symptoms were compared using ANCOVA. The association between changes in insomnia and fatigue severity were determined using Pearson's correlation coefficient.

There were no differences in treatment outcomes between patients with and without co-occurring fatigue and insomnia (CBT-F: mean difference (95% CI) in CIS-fat-score 0.80 (-2.50-4.11), p = 0.63, d = 0.06; CBT-I: mean difference (95% CI) in ISI-score 0.26 (-1.83-2.34), p = 0.80, d = 0.05). Changes in severity of both symptoms were associated (CBT-F: r = 0.30, p < 0.001, CBT-I: r = 0.50, p < 0.001). Among patients no longer severely fatigued after CBT-F, 31% still reported insomnia; of those without clinical insomnia after CBT-I, 24% remained severely fatigued.

CBT-F and CBT-I maintain their effectiveness when severe fatigue and insomnia co-occur. Changes in severity of both symptoms after CBT are associated, but the co-occurring symptom can persist after successfully treating the target symptom.