Insomnia in shift work disorder relates to occupational and neurophysiological impairment

Abstract

Study objectives: To determine whether occupational and neurophysiological decrements within shift work disorder (SWD) are differentially related to its two diagnostic symptoms, insomnia and excessive sleepiness.

Methods: Thirty-four permanent night workers participated in an overnight lab protocol including a multiple sleep latency test (MSLT) and an event-related brain potential (ERP) task testing auditory target detection (P3a and P3b). At 16:00, each subject completed an Endicott Work Productivity Scale (EWPS), two Insomnia Severity Indices (ISI-Day, ISI-Night), and an Epworth Sleepiness Scale (ESS). Subjects were grouped by ISI and ESS scores into clinical phenotypes. This study compared EWPS and ERP results between alert insomniacs ("AI," reporting insomnia without sleepiness), sleepy insomniacs ("SI," reporting both insomnia and sleepiness), and controls.

Results: The AI group was most impaired on the EWPS, significantly more impaired than controls (25.8 ± 14.8 vs. 12.3 ± 9.4, p < 0.05). SI were not statistically different from controls (19.5 ± 8.7 vs. 12.3 ± 9.4, p > 0.05). Compared to controls, AI showed significantly attenuated P3a response (Fcz, Czp, Cpz, mean difference [MD] 1.62-1.77, p < 0.05) and target-detection P3b response (Fcz, Czp, Cpz, MD 1.28-1.64, p < 0.05). P3b in SI was not different from controls (p > 0.10), and P3a was only different at one electrode site (Cpz, MD 1.43, p < 0.01). Neither the MSLT nor the ESS correlated with EWPS scores or ERP (P3a/P3b) amplitudes (p > 0.10). However, the mean of the ISI measurements correlated with the EWPS (r = 0.409, p < 0.01) and the attention-to-novelty P3a (r = -0.410, p < 0.01).

Conclusions: Among shift work disorder patients, insomnia is linked to functional and cognitive impairments. Insomniacs with normal sleepiness showed more severe impairments than insomniacs who also reported excessive sleepiness.

Keywords: Epworth Sleepiness Scale; Insomnia Severity Index; circadian phase; event-related brain potentials; excessive sleepiness; insomnia; multiple sleep latency test; shift work; work productivity.

Figure 1

(A) Illustration of ERP difference waveforms corresponding to each group at FCz and CPz electrodes. (B) Topographical scalp distribution of P3a (200–240 ms) and P3b (340–380 ms) activities evaluated in each group. Positive voltage is colored red, negative voltage is colored blue, and white color corresponds to zero. CO, controls; AI, alert insomniacs; SI, sleepy insomniacs