Correlations among Epworth Sleepiness Scale scores, multiple sleep latencytests and psychological symptoms

The aim of this study was to identify factors other than objective sleep te ndency associated with scores on the Epworth Sleepiness Scale (ESS. There w ere 225 subjects, of whom 40% had obstructive sleep apnoea (OSA), 16%, had simple snoring, and 4.9% had snoring with sleep disruption (upper airway re sistance syndrome); 9.3% had narcolepsy and 7.5% had hypersomnolence withou t REM sleep abnormalities; 12% had chronic fatigue syndrome; 7.5% had perio dic limb movement disorder and 3%, had diurnal rhythm disorders. ESS, the r esults of overnight polysomnography and multiple sleep latency test (MSLT) and SCL-90 as a measure of psychological symptoms were recorded. The ESS sc ore and the mean sleep latency (MSL) were correlated (Spearman rho = -0.30, P<0.0001). The MSL was correlated with total sleep time (TST) and with sle ep efficiency but not with apnoea/hypopnoea index. There was no association between the MSL and any aspect of SCL-90 scores, except a borderline signi ficant association with the somatisation subscale. The ESS was correlated w ith TST but not with sleep efficiency or apnoea/hypopnoea index. The ESS wa s correlated with all subscales of the SCL-90 except psychoticism. An ESS g reater than or equal to 10 had poor sensitivity and specificity as a predic tor of MSL <10 min or MSL <5 min. We conclude that the MSLT and the ESS are not interchangeable. The ESS was influenced by psychological factors by wh ich the MSL was not affected. The ESS cannot be used to demonstrate or excl ude sleepiness as it is measured by MSLT.