The portal for rare diseases and orphan drugs

No clear epidemiological data are available. Narcolepsy type 2 prevalence numbers are controversial, sometimes higher and sometimes lower than those of narcolepsy type 1, depending on reports.

Narcolepsy type 2 manifests generally between the age of 10 and 30 years old, although onset in childhood is rare. Narcolepsy type 2 has a variable phenotype and evolution, with sometimes improvement or even disappearance of the symptoms, rarely the development of cataplexy (conversion to narcolepsy type 1), or a change in the phenotype to idiopathic hypersomnia. It can also be a lifelong disease, with stable symptomatology.

The etiology is still unknown, probably because this disorder is heterogeneous. Reduction of hypocretin-1 levels is found in the cerebrospinal fluid in 10-20% of cases, and in which case the disorder is reclassified narcolepsy type 1. The presence of the HLA DQB1*0602 allele is reported in 40% of cases (more than in the general population but less than in cases of narcolepsy type 1, 98%).

Definitive diagnosis requires the presence of clinical symptoms and characteristics polysomnography findings. Nocturnal and daytime polysomnography demonstrates an average sleep latency of under eight minutes with at least two sleep onset rapid eye movement periods (SOREMP) on multiple sleep latency tests. A pure clinical diagnosis is not possible due to the absence of pathognomonic symptom such as cataplexy, and daytime sleepiness being a non-specific symptom.

Other causes of sleepiness, including narcolepsy type 1, chronic insufficient sleep and idiopathic hypersomnia (especially the form without long sleep time), must be systematically taken into account.

Rare familial cases have been reported; however, the mode of inheritance is unclear.

Treatment is only symptomatic, based on stimulant drugs and a good sleep hygiene (sufficient sleep duration at night is required, with scheduled short naps during the day). Modafinil or pitolisant are the first line treatments with the best benefit/risk ratio. Second-line treatments include methylphenidate, sodium oxybate, solriamfetol or amphetamines.

The disease has a negative impact on scholarly and professional performances. Spontaneous evolution of the disease has not been much studied, but the phenotype and evolution seems variable : stability, disappearance of the symptoms, development of cataplexy (conversion to narcolepsy type 1) , or change to idiopathic hypersomnia.