0767 A Clock That Won’t Stop: Diagnosing Non-24 Sleep–Wake Disorder in a Sighted Adult with Serial Melatonin Profiling

Abstract Introduction Non-24-hour sleep–wake disorder (N24SWD) is uncommon in sighted individuals and often underdiagnosed due to overlapping features with delayed sleep–wake phase disorder or behavioral sleep irregularity. Objective confirmation using serial melatonin profiling and structured sleep diaries in clinical settings is rarely reported. This case highlights the diagnostic value of combining behavioral and physiologic circadian markers in a sighted adult with a long-standing free-running sleep pattern. Methods A 40-year-old sighted male with a >12-year history of progressive sleep–wake delay underwent structured diagnostic evaluation. Data collected included: (1) two-week sleep diary documenting sleep onset/offset patterns, (2) two serial 24-hour salivary melatonin profiles (Salimetrics) performed one week apart, and (3) in-lab polysomnography and home sleep apnea testing. Clinical history, sleep questionnaires, and physical examination findings were integrated with objective circadian markers to establish diagnosis and guide treatment. Results Sleep diary revealed a free-running rhythm with approximately one-hour daily delay in both sleep onset and wake time, while total sleep duration (9–10 hours) and sleep quality remained stable. Despite referral for excessive sleepiness, Epworth Sleepiness Scale scores remained 1 across all assessments. Two 24-hour melatonin profiles demonstrated biologically consistent but progressively delayed melatonin secretion. The first profile showed evening rise and nocturnal peak aligned with the patient’s delayed habitual sleep time. The second profile, one week later, displayed a further several-hour phase shift that mirrored the drift recorded in the sleep diary. Polysomnography showed mild obstructive sleep apnea (AHI 13–14), which did not account for the circadian pattern. The convergence of clinical history, diary-confirmed phase drift, and shifting melatonin rhythms confirmed a diagnosis of N24SWD in a sighted patient. Therapy was initiated with a melatonin receptor agonist taken 1 hour before a fixed 21:00 bedtime, combined with morning bright-light exposure and behavioral schedule anchoring. Conclusion This case highlights that N24SWD can occur in sighted adults and may present with functional impairment rather than subjective sleepiness. Serial melatonin profiling combined with structured sleep-wake documentation can objectively confirm a free-running circadian rhythm and guide targeted entrainment treatment. Support (if any)