A multiple sleep latency test (MSLT) with occurrence of sleep onset REM periods (SOREMP) is considered one of the central diagnostic criteria for narcolepsy according to the International Classification of Sleep Disorders, but its sensitivity and specificity have been questioned. This study aims to describe MSLT and polysomnography (PSG) findings, including frequency and distribution of SOREMP during the day, in a large cohort of patients with central disorders of hypersomnolence (CDH). We retrospectively analyzed electrophysiological data from MSLT and PSG in 370 consecutive patients with narcolepsy type 1 (NT1, n = 97), type 2 (NT2, n = 31), idiopathic hypersomnia (IH, n = 48), nonorganic hypersomnia (NOH, n = 116) and insufficient sleep syndrome (ISS, n = 78). NT1 and NT2 patients had a significantly shorter mean Sleep Latency (mSL) and REM-Latency (REML) in MSLT and PSG. SOREMP occurred more frequently in narcoleptic vs. non-narcoleptic patients in MSLT and PSG. Occurrence of 3 or more SOREMP in MSLT and a SOREMP in PSG had a very high specificity and positive predictive value (98%/96% and 100% respectively), however relatively low sensitivity (65% and 45% respectively). NT1 more than NT2 patients have shorter mSL and more frequent SOREMP in MSLT and shorter SL as well as REML during nocturnal PSG. Increasing numbers of SOREMP in MSLT and especially SOREMP during PSG increase specificity on the expense of sensitivity in diagnosing narcolepsy. Therefore, frequency of SOREMP in MSLT naps and PSG can help to discriminate but not clearly separate narcoleptic from non-narcoleptic patients.

Narcolepsy type 1 (NT1) is a disorder with well‐established markers and a suspected autoimmune aetiology. Conversely, the narcoleptic borderland (NBL) disorders, including narcolepsy type 2, idiopathic hypersomnia, insufficient sleep syndrome and hypersomnia associated with a psychiatric disorder, lack well‐defined markers and remain controversial in terms of aetiology, diagnosis and management. The Swiss Primary Hypersomnolence and Narcolepsy Cohort Study (SPHYNCS) is a comprehensive multicentre cohort study, which will investigate the clinical picture, pathophysiology and long‐term course of NT1 and the NBL. The primary aim is to validate new and reappraise well‐known markers for the characterization of the NBL, facilitating the diagnostic process. Seven Swiss sleep centres, belonging to the Swiss Narcolepsy Network (SNaNe), joined the study and will prospectively enrol over 500 patients with recent onset of excessive daytime sleepiness (EDS), hypersomnia or a suspected central disorder of hypersomnolence (CDH) during a 3‐year recruitment phase. Healthy controls and patients with EDS due to severe sleep‐disordered breathing, improving after therapy, will represent two control groups of over 50 patients each. Clinical and electrophysiological (polysomnography, multiple sleep latency test, maintenance of wakefulness test) information, and information on psychomotor vigilance and a sustained attention to response task, actigraphy and wearable devices (long‐term monitoring), and responses to questionnaires will be collected at baseline and after 6, 12, 24 and 36 months. Potential disease markers will be searched for in blood, cerebrospinal fluid and stool. Analyses will include quantitative hypocretin measurements, proteomics/peptidomics, and immunological, genetic and microbiota studies. SPHYNCS will increase our understanding of CDH and the relationship between NT1 and the NBL. The identification of new disease markers is expected to lead to better and earlier diagnosis, better prognosis and personalized management of CDH.

The Swiss Primary Hypersomnolence and Narcolepsy Cohort Study (SPHYNCS) is a multicenter research initiative to identify new biomarkers in central disorders of hypersomnolence (CDH). Whereas narcolepsy type 1 (NT1) is well characterized, other CDH disorders lack precise biomarkers. In SPHYNCS, we utilized Fitbit smartwatches to monitor physical activity, heart rate, and sleep parameters over 1 year. We examined the feasibility of long-term ambulatory monitoring using the wearable device. We then explored digital biomarkers differentiating patients with NT1 from healthy controls (HC). A total of 115 participants received a Fitbit smartwatch. Using a adherence metric to evaluate the usability of the wearable device, we found an overall adherence rate of 80% over 1 year. We calculated daily physical activity, heart rate, and sleep parameters from 2 weeks of greatest adherence to compare NT1 (n = 20) and HC (n = 9) participants. Compared to controls, NT1 patients demonstrated findings consistent with increased sleep fragmentation, including significantly greater wake-after-sleep onset (p = .007) and awakening index (p = .025), as well as standard deviation of time in bed (p = .044). Moreover, NT1 patients exhibited a significantly shorter REM latency (p = .019), and sleep latency (p = .001), as well as a lower peak heart rate (p = .008), heart rate standard deviation (p = .039) and high-intensity activity (p = .009) compared to HC. This ongoing study demonstrates the feasibility of long-term monitoring with wearable technology in patients with CDH and potentially identifies a digital biomarker profile for NT1. While further validation is needed in larger datasets, these data suggest that long-term wearable technology may play a future role in diagnosing and managing narcolepsy.

Summary: Presence of psychiatric comorbidities is well documented in narcolepsy type‐1 (NT1) but there are limited data on patients with ‘other central disorders of hypersomnolence’ (OCH). This study aimed to investigate frequency of psychiatric comorbidities in patients with NT1 and OCH, and to evaluate their impact on quality of life and sleep as an additive factor in combination with hypersomnolence‐related symptoms. This study was conducted within the scope of the international Swiss Primary Hypersomnolence and Narcolepsy Cohort Study (iSPHYNCS), which aims to find new biomarkers in central disorders of hypersomnolence (CDH). Study participants underwent Mini International Neuropsychiatric Interview and completed questionnaires related to quality of life and sleep. Comparative analysis was conducted to investigate group differences, and multivariable regression models were used to reveal the impact of psychiatric comorbidities. Among a total of 90 patients, 26 were diagnosed with NT1 and 64 with OCH. In all, 38 patients showed at least one psychiatric disorder, 27% of NT1 and 48% of OCH, with female dominance (50% in females versus 23% in males, p < 0.02). Major depressive episodes (n = 29) were most common, followed by suicidality (n = 13). Patients with a psychiatric diagnosis were more fatigued (β = 0.70, p < 0.05), apathic (β = −5.41, p < 0.002), had more disturbed sleep (β = 0.55, p < 0.02), worse sleep (β = 1.89, p < 0.001) and general health (β = −12.55, p < 0.02) quality. Comorbid psychiatric disorders are frequent in patients with CDH and worsen the impact of hypersomnolence‐related symptoms on daily activities regardless of the type of CDH. Psychiatric comorbidities may create a vicious circle with fatigue and avoidance of physical activities, which aggravates hypersomnolence‐related symptoms.

Study Objectives: The boundaries between narcolepsy type 1 (NT1), narcolepsy type 2 (NT2), and idiopathic hypersomnia (IH) and the evolution of these diseases over time are poorly understood. This retrospective cohort single-center study with a cross-sectional follow-up aims to assess changes of diagnosis and test findings over time. Methods: Retrospective and cross-sectional data collection: We assessed demographic characteristics, symptoms, sleep–wake tests, and diagnosis changes in patients with NT1, NT2, or IH seen at the Bern Sleep–Wake Epilepsy center between 2000 and 2021. In addition, we obtained information about changes in symptoms and diagnosis by contacting patients seen between 2005 and 2017 by telephone. The two data sources were combined to analyze the frequency of diagnosis changes. Results: A total of 214 patients (NT1 n = 122, NT2 n = 37, IH n = 55) were included. In 17% (30/179) of patients with follow-up, the diagnosis changed during the observational period. The most unstable diagnosis was NT2 (17/30, 57%), most commonly transitioning to NT1 (n = 5) and IH (n = 9). Five patients with IH went into remission. NT1 was mostly stable (104/107). We confirmed a poor retest reliability of the MSLT in patients with NT2 and IH. Conclusions: Frequent diagnosis changes in patients with NT2 and IH challenge the current diagnostic criteria, in addition, IH can remit.

Kleine-Levin syndrome (KLS) is a rare and debilitating disorder presenting with periodic hypersomnolence, cognitive, psychiatric and behavioral disturbances. In the absence of biomarkers it can be difficult to diagnose. Rare LMOD3 variants in a family and in seven sporadic cases with KLS have been described. Here we report a patient and her family with an unclassified, familial, periodic central disorder of hypersomnolence (CDH) in whom the presence of a LMOD3 gene variant was assessed. The female patient presented since early adulthood with recurrent episodes of hypersomnolence. Over more than 20 years of follow-up the diagnoses of idiopathic hypersomnia, KLS and hypersomnia associated with a psychiatric condition were made. The family history is positive for periodic hypersomnolence and psychiatric conditions. The patient, her symptomatic mother and her asymptomatic sister carried a Proline for Histidine substitution at codon 552 of the LMOD3-gene. This variant was previously reported in two sporadic KLS patients and its frequency in the general population is below 0.02%. We report the association of periodic hypersomnia with a polymorphism of the LMOD3-gene in a patient with atypical KLS and a positive family history. Further research is needed to assess the pathological and predictive value of LMOD3 variants in KLS.