1359 Putting the L and S in KLS: Lithium and Steroids in Adult-Onset Kleine–Levin Syndrome

Introduction Kleine–Levin syndrome (KLS) is a relapsing–remitting hypersomnia characterized by episodic hypersomnolence, cognitive impairment, and behavioral change. Adult-onset cases are rare and may be difficult to distinguish from other neurologic, psychiatric, or sleep-related conditions. Report of case(s) A 39-year-old man developed abrupt hypersomnia shortly after a presumed viral respiratory illness in early 2023. Prior to treatment, he experienced 4–5 episodes per year, with major episodes lasting up to 8 weeks, accompanied by sleeping 18–20 hours per day, profound confusion, derealization, dysarthria, slowed cognition, anorexia, vomiting, and gait instability requiring a cane. These prolonged episodes produced major functional impairment affecting cognition, mobility, independence, and employment. Between episodes, he reliably returned to his baseline level of cognitive and functional functioning. Diagnostic evaluation revealed no alternative etiology. Brain MRI demonstrated a small right frontal extra-axial meningioma without mass effect. Routine EEG capturing wakefulness and sleep onset was normal, with no epileptiform discharges. The cerebrospinal fluid and serum studies were also unremarkable. Polysomnography identified mild obstructive sleep apnea with a central component, effectively treated with continuous positive airway pressure at 9 cm H₂O. Despite optimized therapy, he continued to experience recurrent hypersomnolence and cognitive episodes, confirming that sleep-disordered breathing did not account for the relapsing clinical course. Lithium was initiated for management of recurrent hypersomnia consistent with KLS. After initiation, he demonstrated a dramatic therapeutic response: episodes became far less frequent and shortened to ~10 days, with a reliable return to baseline between episodes. The patient received approximately six periodic 3-day courses of intravenous methylprednisolone during prolonged episodes, each associated with accelerated symptom resolution, as well as one oral corticosteroid course when intravenous therapy was unavailable. In 2025, he experienced only two brief episodes, each markedly shorter than his pre-treatment baseline. The magnitude of improvement observed in this patient is consistent with prior reports describing lithium-associated reductions in episode frequency and duration of ~30–50% and corticosteroid-associated shortening of prolonged episodes by ~1–2 weeks when administered early. Conclusion This case highlights adult-onset Kleine–Levin syndrome triggered by viral illness, persistent symptoms despite optimized CPAP therapy, and substantial improvement with lithium and corticosteroids. Support (if any)