1286 Sleeping Together, Waking Apart: Divergent Sleep Cycles in Conjoined Twins

Abstract Introduction The regulation of sleep, the balance between homeostatic sleep pressure (Process S) and circadian rhythm (Process C), is historically debated as either a humoral phenomenon driven by circulating somnogens or a local neural network process. Craniopagus conjoined twins sharing vasculature, but two separate central nervous systems offer a rare natural model to isolate these variables. We present polysomnographic (PSG) findings in 20-month-old craniopagus twins demonstrating independent sleep-wake cycles and divergent respiratory phenotypes despite shared circulation. Report of case(s) Twenty-month-old female craniopagus twins presented for sleep-disordered breathing evaluation following witnessed positional apnea during anesthesia induction. A modified PSG montage was utilized due to vertical calvarial fusion. Unique "tandem-wedge" positioning with a foam overlay was required to elevate Twin B’s thorax relative to Twin A to prevent cervical hyperflexion. A split-headbox configuration captured accessible frontal and central leads relative to each twin's sagittal midline. Conclusion The twins demonstrated divergent respiratory severity but a shared mechanistic phenotype. Twin A exhibited Mild Obstructive Sleep Apnea (OSA) oAHI 4.0/hr; nadir SpO2 90%. In contrast, Twin B demonstrated Severe OSA oAHI 13.6/hr with profound hypoxemia nadir SpO2 69%. Despite the severity disparity, both twins displayed marked REM-dependent obstruction (REM-AHI 23.6/hr and 44.6/hr, respectively), confirming a shared structural-positional vulnerability exacerbated by REM atonia. Crucially, hypnogram analysis revealed asynchronous sleep-wake states; Twin B sustained consolidated N3 sleep during periods of documented wakefulness in Twin A. The documentation of asynchronous sleep staging and independent arousals suggests sleep pressure is driven by individual, use-dependent neuronal networks rather than circulating humoral factors alone. Despite efforts to optimize alignment with foam overlay and split headbox, we cannot rule out that some discrepancy in apnea severity is from unavoidable neck flexion. More research of conjoined twins of different ages could be useful to further explore the intricacies of sleep mechanisms. Support (if any)