Effect of age on MSLT results in patients with narcolepsy-cataplexy

Objective: To measure the effect of age on Multiple Sleep Latency Test (MSLT) characteristics, sleep latency, and number of sleep-onset REM periods (SOREMP) in two large populations of narcoleptic patients with similar genetic backgrounds. Methods: Clinical and polygraphic information on the severity of the condition was obtained on 236 well-defined narcolepsy-cataplexy-human leukocyte antigen DR2-positive patients from Montpellier (France) and on 147 similar patients from Montreal (Canada). Results: The results show a progressive decrease in the number of SOREMP with age and a progressive increase in the mean sleep latency on the MSLT as a function of age. This finding is also related to the severity of cataplexy as assessed from the clinical history with a progressive decrease in the frequency of cataplexy attacks with age. These results may reflect the progressive increase in sleep latency seen in normal aging and suggest that clinical improvement might be due to changes in the neural mechanisms responsible for SOREMP, which may weaken with age. Conclusions: The progressive decrease in the number of SOREMP and increase in the mean sleep latency on the MSLT as a function of age suggest that the current criteria used for diagnosis may be too stringent in older patients. The major influence of age on MSLT results should therefore be taken into account when diagnosing a narcoleptic patient.