Fibromyalgia syndrome: overnight falls in arterial oxygen saturation

Sleep alterations and muscular changes suggesting hypoxia have been reported in fibromyalgia syndrome (FS) pathophysiology. We tested the hypothesis that patients with FS show falls in the oxygen saturation of hemoglobin in arterial blood (SaO2%) during sleep.

Overnight SaO2% was measured by digital pulse oximetry in 28 randomly selected women who met 1990 American College of Rheumatology criteria for the diagnosis of FS and 15 similar controls. Considering the results of pulse oximetry and in order to evaluate the possible presence of a sleep apnea syndrome (SAS) as the reason for the nocturnal desaturations, the Epworth Sleepiness Scale (ESS) was mailed to the patients and controls. Patients and controls who had a score higher than 10 on the ESS underwent a polysomnographic study.

Patients with FS showed lower overnight minimum SaO2% (86.8 +/- 1.3 versus 90.7 +/- 0.9 in controls, P < 0.05), greater number of desaturations (8.3 +/- 1.8 versus 2.7 +/- 0.8 in controls, P < 0.05) and more desaturations/hour (1.3 +/- versus 0.4 +/- 0.1 in controls, P < 0.05), more night minutes in SaO2% < 92% (56.3 +/- 12.9 versus 9.1 +/- 3.8 in controls, P < 0.01) and more minutes in SaO2% < 90% (14.7 +/- 3.7 versus 2.4 +/- 1.0 in controls, P < 0.05). There were no differences between patients with FS and controls in ESS scores. Five patients (19.2%) in the FS group and 2 (15.4%) in the control group had ESS scores higher than 10. One patient had 1 control subject showed on apnea-plus-hypopnea index higher than 5 (13 and 9, respectively) in polysomnographic study.

Patients with FS showed small overnight falls in SaO2% and spent more time during the night in SaO2% below 92% and 90% than did the control group. These alterations that, as a whole, are not due to the presence of an associated SAS could be important in FS musculoskeletal pathophysiology.