Latest Research

Prevalence and Incidence of Narcolepsy In the US General Population

Maurice M. Ohayon
Marie-Lise Côté

Introduction:
Narcolepsy is a sleep disorder characterized by cataplexy, hypersomnolence, sleep fragmentation and manifestations of various REM sleep abnormalities. It is a rare orphan disorder and therefore, its prevalence is almost exclusively estimated by derivate from clinical samples. Consequently, the objective of this study was to assess the prevalence of narcolepsy in an US general population representative sample.

Materials and methods:
The initial epidemiological study was carried with 15,927 individuals from 15 US States using the Sleep-Eval system. The longitudinal study was carried on in eight of these 15 states. A total of 12,218 subjects were interviewed by phone during the first wave and 10,931 at the second wave three years apart. Prevalence rates were calculated with the large sample while the Incidence was calculated on the subjects who participated in both interviews (N=10,931). The same interview was completed in both waves. For the purpose of this study, an algorithm was created using the answers provided for each symptom to reach a diagnosis conclusion of Narcolepsy type 1 (NT1) or Narcolepsy type 2 (NT2) according to ICSD3.

Results:
NT1 was identified in 0.0126% (95% CI: 0.000% to 0.03%) of the whole sample. Prevalence was similar between men and women. NT1 did not differ significantly by age groups although it was slightly higher in individuals younger than 35 y.o. (0.0201% (95% CI: 0.000% to 0.06%)) compared to 0.016% (95% CI: 0.000% to 0.047%) in the 35 to 54 y.o. group and none in the oldest group. NT2 was observed in 0.0251% (95% CI: 0.0005% to 0.0497%) of the sample. NT2 prevalence was comparable between men and women and among age groups. Overall, 66.7% of narcolepsy individuals in the sample identified by Sleep-Eval were already diagnosed as such by a physician. The incidence rate was also very low at 0.0026% per year.

Conclusions:
Our results support the fact that narcolepsy is indeed a rare disorder affecting 37.7 individuals per 100,000 inhabitants with a relatively low incidence at 2.6 individuals per 100,000 inhabitants per year. Recognition of the disorder by a physician was relatively high in the United States with 2/3 of the cases being already diagnosed.