Twenty-four-hour Skin Temperature Rhythms in Young People With Emerging Mood Disorders: Relationships With Illness Subtypes and Clinical Stage.

While circadian disruptions are common in some sub-groups of youth with mood disorders, skin temperature rhythms in these cohorts are understudied. We examined 24-h wrist skin temperature rhythms in youth with emerging mood disorders, exploring associations with clinical stage and proposed illness subtypes. Youth (n = 306, 23.42 ± 4.91 years, 65% females) accessing mental health care and 48 healthy controls (23.44 ± 3.38 years, 60% females) were examined. Skin temperature parameters including rhythm-adjusted mean temperature, inter-daily stability (day-to-day consistency), intra-daily variability (rhythm fragmentation), and peak temperature time were derived from a wearable sensor. Based on our illness trajectory-pathophysiology model, participants were classified by mood disorder subtypes ("hyperarousal-anxious" [n = 209], "neurodevelopmental-psychosis" [n = 40], or "circadian-bipolar spectrum" [n = 43]), as well as by clinical stage (subthreshold disorders classed as 1a or 1b [n = 47, 173, respectively], and full-threshold disorders as 2+ [n = 76]). Compared to controls, youth with mood disorders had delayed, less stable, and more variable skin temperature rhythms, indicated by lower rhythm-adjusted mean skin temperature (29.94 ± 0.10 °C vs 31.04 ± 0.25 °C, p < 0.001), delayed peak timing (0533 ± 0014 vs 0332 ± 0036, p = 0.002), reduced inter-daily stability (p = 0.009), and increased intra-daily variability (p = 0.020). Peak skin temperature also occurred later relative to sleep midpoint (0.31 ± 0.14 vs -0.48 ± 0.35 radians, p = 0.037). The "circadian-bipolar spectrum" subtype exhibited lower relative amplitude (0.07 ± 0.005 vs 0.08 ± 0.002 [hyperarousal-anxious] and 0.09 ± 0.005 [neurodevelopmental-psychosis], p = 0.039), with no delay in sleep midpoint. Clinical stages were not associated with differences in skin temperature parameters. These findings highlight the potential of use of 24-h skin temperature rhythms as a non-invasive biomarker of circadian disturbances in youth with emerging mood disorders. The observed disruptions in temperature patterns and rhythmicity support the notion that disrupted circadian rhythms may mediate the onset or illness course of some subgroups of youth with emerging major mood disorders.