Narcolepsy without cataplexy: 2 subtypes based on CSF hypocretin-1/orexin-A findings.

STUDY

OBJECTIVES

Cerebrospinal fluid (CSF) hypocretin-1 levels and their relationship with the clinical characteristics of narcolepsy without cataplexy have not been well elucidated. Our aim was to examine whether clinical characteristics vary with CSF hypocretin-1 levels among narcoleptic patients without cataplexy.

DESIGN

Clinical features, variables on the multiple sleep latency test, and results of HLA typing were correlated with CSF hypocretin-1 levels.

SETTING

University-based sleep laboratories and a sleep disorders center.

PATIENTS: Seventeen patients (5 male, 12 female) who fulfilled the diagnostic criteria of narcolepsy without cataplexy according to the International Classification of Sleep Disorders. INERVENTIONS: Patients underwent lumbar puncture for CSF sampling.

MEASUREMENTS AND

RESULTS

Five patients showed a markedly decreased CSF hypocretin-1 level, whereas the remaining 12 patients showed almost normal levels. The mean rapid eye movement (REM) latency was significantly shorter and the age at onset was significantly earlier in the low CSF hypocretin-1 group compared with the normal CSF hypocretin-1 group. HLA-DR2 was positive in all of the patients with low CSF hypocretin-1, whereas only 33.3% of patients with normal CSF hypocretin-1 were DR2 positive.

CONCLUSIONS

Some narcoleptic patients without cataplexy have low CSF hypocretin-1 levels. In patients who have narcolepsy without cataplexy, short mean REM latency, younger age at onset, and HLA-DR2 are associated with CSF hypocretin-1 deficiency. Markedly decreased CSF hypocretin-1 levels could be a significant marker for identifying subgroups of narcolepsy patients without cataplexy.