Introduction Sleepiness is a subjective symptom, often reported by patients with sleep disorders. We investigated subjective measures of sleepiness, as measured by the Epworth Sleepiness Scale (ESS), and correlated this to objective observations, as recorded by the mean sleep latency (MSL). We related our findings to affect, fatigue, emotion, mood, and quality of life.
Patients and methods Patients referred to a tertiary referral centre for sleep disorders were assessed regarding their sleep complaint, excessive daytime sleepiness (EDS), sleep routine and night-time symptoms. Age, gender and BMI were recorded. The ESS (0–24 points), the Stanford Sleepiness Scale (SSS; 0–8 points), the Samn-Perrelli fatigue scale (SPS; 0–7 points), the Global Vigour and Affect Scale (GVS and GAS 0–10 points, respectively), the Hospital Anxiety and Depression Scale (HADS-A and HADS-D 0–21 points, respectively), and the Positive and Negative Affect Schedule (PAS and NAS 10–50 points, respectively) were recorded. Patients underwent polysomnography (PSG) and multiple sleep latency tests (MSLT).
Results 9 patients (5 male/4 female, age 44.1 (14.6) years, BMI 30.5 (6.7) kg/m2; obstructive sleep apnoea (OSA, n = 4), narcolepsy (n = 2), idiopathic hypersomnia (n = 1), insomnia (n = 1), no sleep disorder (n = 1)) were studied. The PSG results showed a short total sleep time (TST 360.1 (69.7) min) with a slightly reduced sleep efficiency (SE 79.6 (11.4)%), there were no relevant periodic limb movements (PLM index 7.3 (4.3)/h) but mild-moderate OSA (apnoea-hypopnoea index (AHI) median 6.4(interquartile range 0.2–30.5)/h). The ESS was 13.9 (7.2) points, the MSL was 7.6 (5.9) min, the SSS was 3.0 (1.3) points and the SPS was 4.0 (1.3) points. The GVS was 5.6 (2.2) points and the GAS was 4.8 (1.6) points, the HADS-A was 8.7 (6.2) points and the HADS-D was 8.9 (5.9) points, the PAS was 23.9 (10.7) and the NAS was 25.6 (8.0) points. There was a positive correlation between the ESS and the SPS, but no other significant correlations (Table 1).
Conclusion The ESS and the MSL did not correlate well, nor did they relate to measures of affect, emotion, mood, or quality of life. Conversely, there was an interaction between measures of fatigue and the ESS. These findings emphasise the need to develop better scores to characterise EDS, other than the ESS.