Study objectives: To evaluate the impact of obstructive sleep apnea syndrome (OSAS) on serum creatine phosphokinase (CK) levels.
Design: Single-center prospective cross-sectional study.
Setting: Academic sleep disorder center.
Patients: Two hundred one consecutive patients (mean [± SD] age, 54.9 ± 11.0 years; 155 men and 46 women; mean body mass index, 31.3 ± 6.9 kg/m2) with suspected sleep-disordered breathing.
Measurements and results: OSAS was confirmed in182 patients (apnea-hypopnea index [AHI], > 5 events per hour) and was ruled out in 19 patients (control subjects) by standard polysomnography. Sixty-six OSAS patients and 1 control patient showed an unexplained CK elevation. The mean baseline CK level was significantly higher in patients with severe OSAS (AHI, > 30 event per hour; n = 89) compared to those with mild-to-moderate OSAS (AHI, 5 to 30 events per hour; n = 93) and control subjects (191.4 ± 12.9 vs 134.3 ± 7.5 vs 107.1 ± 7.9 U/L, respectively; p < 0.01). Receiver operating curve analysis identified an optimal cutoff value of > 148 U/L (r = 0.660) for CK, which yielded a positive predictive value of 99%, a sensitivity of 43%, and a specificity of 95% for the diagnosis of OSAS. The mean nocturnal oxyhemoglobin saturation was the main predictor of CK level (r = 0.47; p < 0.001). Continuous positive airway pressure (CPAP) treatment resulted in a significant decline of CK levels both in patients with mild-to-moderate OSAS (n = 38; 129.7 ± 13.4 vs 96.7 ± 7.6 U/L, respectively; p < 0.001) and in patients with severe OSAS (n = 39; 187.7 ± 18.9 vs 132.2 ± 12.9 U/L, respectively; p < 0.001).
Conclusions: One third of our study population showed a mild-to-moderate elevation in CK level, which was highly predictive of OSAS. The application of CPAP therapy in OSAS patients resulted in a significant decrease in CK level. We speculate that OSAS may account for a substantial number of cases of unexplained CK elevation (ie, hyperCKemia). Further studies should address the prevalence of OSAS in patients with mild-to-moderate hyperCKemia.