Perception of induced dyspnea in fibromyalgia and chronic fatigue syndrome

Dyspnea perception is distorted in patients with medically unexplained dyspnea. The goals of this study were 1) to replicate these results in patients with fibromyalgia and/or chronic fatigue syndrome (CFS), and 2) to investigate predictors of distorted symptom perception within the patient group, with a focus on negative affectivity (NA), psychiatric comorbidity and somatic symptom severity.

Seventy-three patients diagnosed with fibromyalgia and/or CFS and 38 healthy controls (HC) completed a rebreathing paradigm, consisting of a baseline (60s of room air), a rebreathing phase (150s, gradually increasing ventilation, partial pressure of CO₂ in the blood, and self-reported dyspnea), and a recovery phase (150s of room air). Dyspnea, respiratory flow and FetCO₂ levels were measured continuously.

Patients reported more dyspnea than HC in the recovery phase (p=0.039), but no differences between patients and HC were found in the baseline (p=0.07) or rebreathing phase (p=0.17). No significant differences between patients and HC were found in physiological reactivity. Within the patient group, the effect in the recovery phase was predicted by somatic symptom severity (p=0.046), but not by negative affectivity or by the number of psychiatric comorbidities.

This study extended earlier findings in patients with medically unexplained dyspnea to patients with fibromyalgia and CFS. This suggests that altered symptom perception is a non-symptom-specific mechanism underlying functional somatic syndromes in general, particularly in patients with high levels of somatic symptom severity. The results are discussed in a predictive coding framework of symptom perception.