Narcolepsy/cataplexy. IV: Diagnostic value of daytime nap recordings.

Sleep and wakefulness patterns in daytime naps of 50 patients with narcolepsy/cataplexy were compared with those of 50 controls. Each subject was monitored polygraphically during 2 one-hour nap periods. A sleep-onset REM period in either of the 2 daytime naps was observed to have a higher diagnostic sensitivity (78%) than an abnormally shortened sleep latency (68%). However, the specificities of a sleep-onset REM period (88%) or abnormally shortened sleep latency (90%) were quite similar. When the occurrence of either a sleep-onset REM period or a shortened sleep latency was evaluated in either of the two naps, the overall sensitivity was increased to 84% while the specificity was decreased only to 80%. The limitations of and indications for the use of testing for sleep and REM latencies in the diagnosis of narcolepsy in clinical practice are discussed.