Differential sleep, sleepiness, and neurophysiology in the insomnia phenotypes of shift work disorder.

🎖️ Top 10% JournalOct 18, 2014Sleep

Differences in sleep, tiredness, and brain activity in types of insomnia linked to shift work disorder

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Abstract

34 permanent night workers were classified into three subgroups based on insomnia symptoms and sleepiness.

The alert insomniacs group exhibited normal sleepiness scores but heightened brain activity indicating cortical hyperarousal.
The sleepy insomniacs group displayed significantly low sleepiness scores, suggesting a different type of insomnia.
Both insomnia groups did not differ significantly in circadian phase, but controls showed a significant phase delay.
Alert insomniacs experienced longer sleep latencies and lower sleep efficiency compared to controls during both night and day.
Genetic analysis revealed that 9 out of 10 shift workers with excessive sleepiness carried a specific genetic variant associated with sleep patterns.

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STUDY OBJECTIVES: To characterize and compare insomnia symptoms within two common phenotypes of Shift Work Disorder.

DESIGN: Observational laboratory and field study.

SETTING: Hospital sleep center.

PARTICIPANTS: 34 permanent night workers. Subjects were classified by Epworth Sleepiness Scale and Insomnia Severity Index into 3 subgroups: asymptomatic controls, alert insomniacs (AI), and sleepy insomniacs (SI).

MEASUREMENTS: Sleep parameters were assessed by sleep diary. Circadian phase was evaluated by dim-light salivary melatonin onset (DLMO). Objective sleepiness was measured using the multiple sleep latency test (MSLT). Brain activity was measured using the N1 event-related potential (ERP). A tandem repeat in PER3 was genotyped from saliva DNA.

RESULTS: (1) AI group showed normal MSLT scores but elevated N1 amplitudes indicating cortical hyperarousal. (2) SI group showed pathologically low MSLT scores but normal N1 amplitudes. (3) AI and SI groups were not significantly different from one another in circadian phase, while controls were significantly phase-delayed relative to both SWD groups. (4) AI showed significantly longer sleep latencies and lower sleep efficiency than controls during both nocturnal and diurnal sleep. SI significantly differed from controls in nocturnal sleep parameters, but differences during diurnal sleep periods were smaller and not statistically significant. (5) Genotype × phenotype χ² analysis showed significant differences in the PER3 VNTR: 9 of 10 shift workers reporting sleepiness in a post hoc genetic substudy were found to carry the long tandem repeat on PER3, while 4 of 14 shift workers without excessive sleepiness carried the long allele.

CONCLUSIONS: Our results suggest that the sleepy insomnia phenotype is comprehensively explained by circadian misalignment, while the alert insomnia phenotype resembles an insomnia disorder precipitated by shift work.

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