1358 Diagnostic Value of 24-Hour Polysomnography in Suspected Idiopathic Hypersomnia: A Four-Case Series

Abstract Introduction Idiopathic hypersomnia (IH) is difficult to diagnose because standard polysomnography (PSG) and the multiple sleep latency test (MSLT) have limited sensitivity and poor test–retest reliability. Many patients with clinically suspected IH have nondiagnostic MSLT results. Objective diagnostic criteria include either a mean sleep latency ≤8 minutes with ≤1 Sleep Onset REM Period (SOREMP) on MSLT or a total sleep time (TST) >11 hours documented by 24-hour PSG or by actigraphy with sleep diary under unrestricted sleep conditions. Standard overnight PSG often does not capture prolonged sleep duration, and extended sleep recordings have emerged as useful adjuncts when routine testing is inconclusive. We present four cases in which 24-hour PSG clarified the diagnosis in patients with suspected IH despite nondiagnostic MSLT results. Report of case(s) We describe four females aged 20–41 years evaluated for suspected IH with standard overnight PSG and MSLT. Because these initial studies were nondiagnostic and clinical suspicion for IH remained high, each patient subsequently underwent a 24-hour PSG. Overnight PSG findings showed TSTs ranging from 375.0 to 500.0 minutes and REM latencies of 91.0–133.5 minutes. All four MSLTs were nondiagnostic, with mean sleep latencies of 10.1–16.0 minutes and 0–2 SOREMPs, failing to meet objective IH criteria. In contrast, 24-hour PSG demonstrated substantially prolonged sleep duration in every case, with TSTs of 738.0, 714.0, 687.0, and 930.0 minutes and extended REM latencies. These recordings revealed total sleep times exceeding the threshold supportive of IH and provided diagnostic clarity not captured by routine PSG and MSLT testing. Conclusion Across these cases, standard PSG and MSLT were nondiagnostic, whereas 24-hour PSG consistently revealed prolonged sleep duration meeting objective IH criteria. These findings support incorporating extended sleep recordings into the diagnostic evaluation of suspected IH, particularly in patients whose symptoms strongly suggest IH but whose routine studies are inconclusive. By providing an objective measure of total sleep time, 24-hour PSG can enhance diagnostic accuracy and better align objective testing with clinical presentation. Support (if any)