PSG-MSLT for CDH diagnosis requires discontinuation of sleep-modifying medications at least 14 days (6 weeks for fluoxetine) prior and urine toxicology (UTOX) at testing. International Classification of Sleep Disorders-3 TR (ICSD-3-TR) criteria require mean sleep latency (MSL) <8 minutes to diagnose idiopathic hypersomnia (IH), plus >2 sleep-onset REM periods (SOREMPs) for narcolepsy type 1/2 (NT1/NT2). Accurate diagnosis is critical for treatment outcomes and to reduce diagnostic delay.

Of 786 cases, 90 (11.4%) met clinical criteria for NT1, 155 (19.7%) NT2, 314 (39.9%) IH, and 227 (28.9%) were undifferentiated (UH). Medication withdrawal at appropriate time occurred in 342/786 (43.5%) overall, 51/90 NT1 (56.7%), 70/155 NT2 (45.2%), 119/314 IH (37.9%), and 102/227 UH (44.9%). REM-suppressing medications had the highest non-adherence, representing 54.7% non-adherent cases (243/444). Adherence to medication guidelines for NT1/NT2 was associated with satisfying ICSD-3-TR diagnostic criteria vs those non-adherent (NT1: 86.3% vs 64.1% (P=0.014); NT2: 75.7% vs 60.0% (P=0.038)). No difference was found for IH (56.3% vs 60.0% (P=0.52)). Cannabinoids were the most common substance detected by UTOX, found in 33/786 (4.20%), but did not affect ICSD-3-TR criteria satisfaction.

Recommended medication withdrawal increased diagnostic accuracy of the PSG-MSLT for NT1 and NT2 but not IH. Diagnostic accuracy in IH was poor.  The impact of cannabinoids on MSLT outcomes warrants further investigation given their use in patients with suspected CDH.