Validation of the ICSD-2 criteria for CSF hypocretin-1 measurements in the diagnosis of narcolepsy in the Danish population

Abstract

Study objectives: The International Classification of Sleep Disorders (ICSD-2) criteria for low CSF hypocretin-1 levels (CSF hcrt-1) still need validation as a diagnostic tool for narcolepsy in different populations because inter-assay variability and different definitions of hypocretin deficiency complicate direct comparisons of study results.

Design and participants: Interviews, polysomnography, multiple sleep latency test, HLA-typing, and CSF hcrt-1 measurements in Danish patients with narcolepsy with cataplexy (NC) and narcolepsy without cataplexy (NwC), CSF hcrt-1 measurements in other hypersomnias, neurological and normal controls. Comparisons of hypocretin deficiency and frequency of HLA-DQB1*0602-positivity in the Danish and eligible NC and NwC populations (included via MEDLINE search), by (re)calculation of study results using the ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean).

Measurements and results: In Danes, low CSF hcrt-1 was present in 40/46 NC, 3/14 NwC and 0/106 controls (P < 0.0001). Thirty-nine of 41 NC and 4/13 NwC patients were HLA-DQB1*0602-positive (P < 0.01). Hypocretin-deficient NC patients had higher frequency of cataplexy, shorter mean sleep latency, more sleep onset REM periods (P < 0.05) and more awakenings (NS) than did NC patients with normal CSF hcrt-1. Across populations, low CSF hcrt-1 and HLA-DQB1*0602-positivity characterized the majority of NC (80% to 100%, P = 0.53; 80% to 100%, P = 0.11) but a minority of NwC patients (11% to 29%, P = 0.75; 29% to 89%, P = 0.043).

Conclusion: The study provides evidence that hypocretin deficiency causes a more severe NC phenotype. The ICSD-2 criterion for low CSF hcrt-1 (< 30% of normal mean) is valid for diagnosing NC, but not NwC. HLA-typing should precede CSF hcrt-1 measurements because hypocretin deficiency is rare in HLA-DQB1*0602-negative patients.

Figure 1

No correlation between CSF hcrt-1 levels and disease duration of Danish patients with narcolepsy with cataplexy (r = 0.12, P = 0.44). Every circle represents the CSF hcrt-1 level and the disease duration of an individual patient.

Figure 2

CSF hcrt-1 values in the Danish patients with narcolepsy with cataplexy, narcolepsy without cataplexy, other hypersomnias, neurological disorders, and normal controls. Every circle represents the CSF hcrt-1 level of an individual patient or control. The upper horizontal line marks the lower limit of the normal area (2 SD below the mean value of the normal controls). The lower horizontal line marks the cutoff limit for a low CSF hcrt-1 value (30% of the mean value of the normal controls [ICSD-2 criterion]). § Significantly lower mean CSF hcrt-1 value compared to all other groups (P < 0.0001).

Figure 3

Temperature and time stability of CSF hcrt-1 levels in normal controls. Comparison of hcrt-1 levels in CSF immediately frozen (−80°C) or stored for respectively 24, 48, and 96 hours at room temperature (RT) or 4°C before frozen (−80°C). § indicates significantly lower mean value (P < 0.0001)