Applicability of the Sustained Attention to Response Task (SART) in hypersomnolence: Experience and results from a tertiary referral center

OBJECTIVE/BACKGROUND

Evaluation of hypersomnolence disorders ideally includes an assessment of vigilance using the short Sustained Attention to Response Task (SART). We evaluated whether this task can differentiate between hypersomnolence disorders, whether it correlates with subjective and objective sleepiness, whether it is affected by the time of day, and symptoms of anxiety and depression.

PATIENTS/METHODS

We analyzed diagnostic data of 306 individuals with hypersomnolence complaints diagnosed with narcolepsy type 1 (n=100), narcolepsy type 2 (n=20), idiopathic hypersomnia (n=49), obstructive sleep apnea (n=27) and other causes or without explanatory diagnosis (n=110). We included the Multiple Sleep Latency Test (MSLT), polysomnography, Epworth Sleepiness Scale (ESS), Hospital Anxiety and Depression Scale and SART, which were administered five times during the day (outcomes: reaction time, total, commission and omission errors).

RESULTS

The SART outcomes did not differ between groups when adjusted for relevant covariates. Higher ESS scores were associated with longer reaction times and more commission errors (p<.01). The main outcome, total errors, did not differ between times of the day. Reaction times and omission errors were impacted (p<.05).

CONCLUSIONS

The SART quantifies disturbed vigilance, an important dimension of disorders of hypersomnolence. Results do not suggest that depressive symptoms influence SART outcomes. A practice session is advised. Testing time should be taken into account when interpreting results. We conclude that the SART does not differentiate between central disorders of hypersomnolence. It may be a helpful addition to the standard diagnostic workup and monitoring of these disorders.

Hypocretin-1 measurements in cerebrospinal fluid using radioimmunoassay: within and between assay reliability and limit of quantification

Study Objectives

The most sensitive and specific investigative method for the diagnosis of narcolepsy type 1 (NT1) is the determination of hypocretin-1 (orexin-A) deficiency (≤110 pg/mL) in cerebrospinal fluid using a radioimmunoassay (RIA). We aimed to assess the reliability of the Phoenix Pharmaceuticals hypocretin-1 RIA, by determining the lower limit of quantification (LLOQ), the variability around the cutoff of 110 pg/mL, and the inter- and intra-assay variability.

Methods

Raw data of 80 consecutive hypocretin-1 RIAs were used to estimate the intra- and inter-assay coefficient of variation (CV). The LLOQ was established and defined as the lowest converted concentration with a CV <25%; the conversion is performed using a harmonization sample which is internationally used to minimize variation between RIAs.

Results

The mean intra-assay CV was 4.7%, while the unconverted inter-assay CV was 28.3% (18.5% excluding 2 outliers) and 7.5% when converted to international values. The LLOQ was determined as 27.9 pg/mL. The intra-assay CV of RIAs with lower specific radioactive activity showed a median of 5.6% (n = 41, range 1.6%–17.0%), which was significantly higher than in RIAs with higher specific activity (n = 36; median 3.2%, range 0.4%–11.6%, p = .013). The CV around the 110 pg/mL cutoff was <7%.

Conclusions

Hypocretin-1 RIAs should always be harmonized using standard reference material. The specific activity of an RIA has a significant impact on its reliability, because of the decay of ¹²⁵I radioactivity. Values around the hypocretin-1 cut-off can reliably be measured. Hypocretin-1 concentrations below 28 pg/mL should be reported as “undetectable” when measured with the Phoenix Pharmaceuticals RIA.

Clinical Trial Information

This study is not registered in a clinical trial register, as it has a retrospective database design

Intermediate hypocretin-1 cerebrospinal fluid levels and typical cataplexy: their significance in the diagnosis of narcolepsy type 1

STUDY OBJECTIVES

The diagnosis of narcolepsy type 1 (NT1) is based upon the presence of cataplexy and/or a cerebrospinal fluid (CSF) hypocretin-1/orexin-A level ≤ 110 pg/mL. We determined the clinical and diagnostic characteristics of patients with intermediate hypocretin-1 levels (111-200 pg/mL) and the diagnostic value of cataplexy characteristics in individuals with central disorders of hypersomnolence.

METHODS

Retrospective cross-sectional study of 355 people with known CSF hypocretin-1 levels who visited specialized Sleep-Wake Centers in the Netherlands. For n = 271, we had full data on cataplexy type ("typical" or "atypical" cataplexy).

RESULTS

Compared to those with normal hypocretin-1 levels (>200 pg/mL), a higher percentage of individuals with intermediate hypocretin-1 levels had typical cataplexy (75% or 12/16 vs 9% or 8/88, p < .05), and/or met the diagnostic polysomnographic (PSG) and Multiple Sleep Latency Test (MSLT) criteria for narcolepsy (50 vs 6%, p < .001). Of those with typical cataplexy, 88% had low, 7% intermediate, and 5% normal hypocretin-1 levels (p < .001). Atypical cataplexy was also associated with hypocretin deficiency but to a lesser extent. A hypocretin-1 cutoff of 150 pg/mL best predicted the presence of typical cataplexy and/or positive PSG and MSLT findings.

CONCLUSION

Individuals with intermediate hypocretin-1 levels or typical cataplexy more often have outcomes fitting the PSG and MSLT criteria for narcolepsy than those with normal levels or atypical cataplexy. In addition, typical cataplexy has a much stronger association with hypocretin-1 deficiency than atypical cataplexy. We suggest increasing the NT1 diagnostic hypocretin-1 cutoff and adding the presence of clearly defined typical cataplexy to the diagnostic criteria of NT1. Clinical trial information: This study is not registered in a clinical trial register, as it has a retrospective database design.