Drs. Krahn and Gonzalez-Arriaza Reply

To the Editor: We appreciate the comments of Dr. Rack and colleagues that remind us of the importance of interpreting sleep laboratory test results in a clinical context. We agree that the Multiple Sleep Latency Test is a valuable diagnostic tool. Nonetheless, the role of the clinician is to correlate the Multiple Sleep Latency Test findings with the patient’s clinical presentation. In this instance, the presence of long-standing excessive daytime sleepiness, spells consistent with clear-cut cataplexy, sleep paralysis, and vivid dreams greatly increased the likelihood of narcolepsy. We concur that the sleep testing was performed under less-than-optimal conditions in view of the patient’s delayed sleep phase and chronic partial sleep deprivation. If the patient’s symptoms had been limited to excessive daytime sleepiness, the Multiple Sleep Latency Test findings would have been less persuasive. In the presence of the classic tetrad of narcoleptic symptoms and given that the Multiple Sleep Latency Test results were dramatically abnormal (mean initial sleep latency of 30 seconds and sleep onset of REM sleep at all four naps), we believe that this test confirmed the clinical diagnosis of narcolepsy with cataplexy (1).

Many patients with narcolepsy are now recognized to have sleep maintenance difficulties, which sometimes makes performing a Multiple Sleep Latency Test under optimal conditions, while desirable, at times difficult to achieve. Relying solely on the clinical assessment for establishing the diagnosis of narcolepsy, in our opinion, is not sufficient. The relative lack of physician education regarding narcolepsy, the wide range of cataplectic spells, and the potential need after diagnosis to provide lifelong treatment with medications with abuse potential underscore the need for as much objective data as possible.