Perception of induced dyspnea in fibromyalgia and chronic fatigue syndrome

Objective: 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. Methods: Seventy-three patients diagnosed with fibromyalgia and/or CFS and 38 healthy controls (HC) completed a rebreathing paradigm, consisting of a baseline (60 s of room air), a rebreathing phase (150 s, gradually increasing ventilation, partial pressure of CO2 in the blood, and self-reported dyspnea), and a recovery phase (150 s of room air). Dyspnea, respiratory flow and FetCO(2) levels were measured continuously. Results: 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. Conclusion: 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.