Distinct daytime sleepiness phenotypes across insomnia symptom dimensions in the Wisconsin sleep cohort

Insomnia symptoms are heterogeneous, and it remains unclear whether difficulty initiating sleep (DIS), difficulty maintaining sleep (DMS), operationalized as repeated nighttime awakening, and early morning awakening (EMA) correspond to distinct joint patterns of subjective daytime sleepiness and physiological sleep propensity. We examined these symptom-specific phenotypes and their clinical burden.

We analyzed 881 Wisconsin Sleep Cohort participants with complete Epworth Sleepiness Scale (ESS) and Multiple Sleep Latency Test (MSLT) data. Four phenotypes were defined by ESS >10 and MSLT <8 min: Neither, Subjective-only, Objective-only, and Both. DIS, DMS, and EMA were assessed using self-reported questionnaire items and were entered simultaneously in adjusted multinomial logistic regression.

Greater DIS severity was associated with lower ESS (β = -0.70, 95% confidence interval (CI) -1.02 to -0.39), longer MSLT latency (β = 0.45 min, 95% CI 0.10 to 0.80), and lower relative risk of Both (relative risk ratio (RRR) = 0.67, 95% CI 0.52 to 0.87). Greater DMS severity was associated with higher ESS (β = 0.43, 95% CI 0.20 to 0.66) and higher relative risk of Both (RRR = 1.30, 95% CI 1.09 to 1.56). EMA was not associated with the overall phenotype distribution. Within frequent DMS, Subjective-only sleepiness was associated with higher depression and trait anxiety after false discovery rate adjustment.

DIS and DMS were associated with different daytime sleepiness profiles. Within frequent DMS, subjective sleepiness identified greater psychological burden. The observed associations were generally modest and support considering nocturnal symptom pattern when interpreting daytime sleepiness.