Hippocampal volume and memory in narcoleptics with cataplexy

Background/ObjectiveThe objective of this study was to investigate the differences in hippocampal volume (HV) between narcoleptics and normal controls and determine if HV is associated with memory function in narcoleptics. Left and right HV and intracranial volumes (ICV) were manually measured and compared between two groups.MethodsThe study consisted of 36 drug-naïve narcoleptics with cataplexy and 36 age- and sex-matched controls (mean age 29.0 years). All subjects underwent 1.6-mm-thick spoiled gradient recalled magnetic resonance imaging and took the Korean California Verbal Learning Test and the Rey Complex Figure Test to assess verbal and visual memory.ResultsThe mean ICV was not different between groups (1599.2 cm3 in narcoleptics vs. 1623.5 cm3 in controls, p = .450). Bilateral mean HVs were significantly smaller in narcoleptics (left, 2907.2 mm3 in narcoleptics vs. 3092.3 mm3 in controls, p = 0.005; right, 2990.8 mm3 in narcoleptics vs. 3184.3 mm3 in controls, p = 0.004). Significance of HV differences between groups remained after corrections were made for gender, age, and ICV. In narcoleptics, bilateral HV was positively correlated with mean sleep and REM sleep latencies in Multiple Sleep Latency Tests. Absolute memory scores were not different between groups and were not correlated with HV in narcoleptics.ConclusionsNarcoleptics had smaller bilateral HVs compared to controls. HV had a significant relationship with sleep and REM sleep latencies. This study provides supportive evidence of the functional and anatomical deficits in medial temporal areas that are related to the severity of narcolepsy.