Disorders of Arousal and Sleep-Related Hypermotor Epilepsy in adults: a challenging but necessary and critical distinctive diagnosis

BACKGROUND: Sleep-related Hypermotor Epilepsy (SHE) and Disorders of Arousal (DoA) are two conditions that, despite originating from distinct etiological mechanisms, share the manifestation of complex motor behaviours emerging from sleep. Their overlapping clinical features have long posed challenges for differential diagnosis, particularly in adults. SUMMARY: Both SHE and DoA exhibit a close relationship with sleep physiology; consequently, increasing attention has recently been devoted to the neurophysiological mechanisms underlying these motor phenomena, with a specific focus on sleep microstructure and arousal system dynamics. K-complexes may play a key role in the onset of SHE seizures, as evidenced by the tendency of seizures to occur in quasi-periodic clusters at frequencies consistent with K-complexes and other physiological oscillations during light sleep. Analyses of the Cyclic Alternating Pattern (CAP), an EEG marker of sleep instability, have shown that epileptic activity is not uniformly distributed across NREM sleep but is instead enhanced during specific CAP subtypes. A similar pattern has been observed in DoA, with episodes frequently arising during CAP phase A. The sleep instability observed in both SHE and DoA suggests that transient cortical activations may act as triggers for motor events, facilitating the expression of innate motor patterns through subcortical circuit activation. Although distinct in origin, physiological in DoA and epileptic in SHE, both disorders reflect altered arousal regulation and disrupted cortical-subcortical interactions. KEY MESSAGES: This review aims to provide an integrated neurophysiological perspective on SHE and DoA, emphasising their distinctive mechanisms and the broader implications for understanding sleep-related motor behaviours.