The additive impact of periodic limb movements during sleep on inflammation in patients with obstructive sleep apnea.

RATIONALE: Both periodic limb movements during sleep (PLMS) and obstructive sleep apnea (OSA) are major causes of sleep disorders and have been associated with systemic inflammation and cardiovascular events. However, it is uncertain whether in combination they promote a higher inflammatory response and greater risk of cardiovascular events than each condition alone.

OBJECTIVES: To investigate whether the presence of PLMS is associated with increased inflammation in patients suspected of having OSA.

METHODS: In 342 patients who underwent polysomnography to diagnose OSA, plasma C-reactive protein (CRP) and fibrinogen levels were measured.

MEASUREMENTS AND MAIN RESULTS: OSA was found in 254 patients, with 46 also having PLMS. Among the 88 patients who did not have OSA, 8 had PLMS. Plasma CRP and fibrinogen levels in the group with both PLMS and OSA were higher than in patients with neither OSA nor PLMS and in patients with OSA only (CRP: 0.20 ± 0.48 vs. 0.09 ± 0.15 vs. 0.13 ± 0.18 mg/dl, P = 0.03; fibrinogen: 298.2 ± 76.1 vs. 269.0 ± 57.1 vs. 270.0 ± 52.6 mg/dl, P < 0.01). Multivariate analysis showed that the presence of PLMS was associated with higher plasma CRP levels (β = 0.1401, P < 0.01) and fibrinogen levels (β = 0.1359, P = 0.01) independently from other clinical variables such as body mass index and the severity of OSA.

CONCLUSIONS: PLMS were positively associated with plasma CRP and fibrinogen levels in patients suspected of having OSA. Because plasma levels of these proteins have been established as predictive factors of future cardiovascular events, the presence of PLMS may be a useful clinical sign to identify patients with OSA at high risk of cardiovascular events.