Narcolepsy Workup: Approach Considerations, Sleep Studies

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Narcolepsy

Workup

Approach Considerations

Sleep studies are an essential part of the evaluation of patients with possible narcolepsy. The combination of an overnight polysomnogram (PSG) followed by a multiple sleep latency test (MSLT) can provide strongly suggestive evidence of narcolepsy while excluding other sleep disorders.

Human leukocyte antigen (HLA) typing may provide collateral data, but it is more useful for excluding the diagnosis by documenting that the patient does not have either DQB1*0602 or DQA1*0602. HLA typing is less valuable for confirming the diagnosis, in that HLA-DR2 and DQw1 are present in 20-30% of the general population.

Measurement of hypocretin (orexin) levels in the cerebrospinal fluid (CSF) may help establish the diagnosis.^[16]CSF hypocretin levels lower than 110 pg/mL are included in the diagnostic criteria for narcolepsy in the second edition of the International Classification of Sleep Disorders (ICSD-2). On the other hand, high CSF hypocretin levels do not exclude the diagnosis of narcolepsy.

In most cases, imaging studies are unrevealing. A few small studies have implicated magnetic resonance imaging (MRI) changes of the pons within the reticular activating system. Imaging studies such as MRI are useful for excluding rare causes of symptomatic narcolepsy. Structural abnormalities of the brain stem and diencephalon may present as idiopathic narcolepsy. In patients with secondary narcolepsy, MRI of the brain may show various abnormalities that correspond to the underlying cause.

Sleep Studies

An overnight PSG followed by an MSLT can exclude other causes of excessive daytime sleepiness (EDS), especially sleep apnea, and can provide information about EDS by measuring sleep latency and sleep-onset rapid eye movement periods (SOREMPs). The overnight PSG findings typically are normal in narcolepsy, though they may show sleep fragmentation. All central nervous system (CNS) stimulants and sedative-hypnotics should be discontinued 2 weeks before the PSG and MSLT.

The MSLT involves 5 opportunities to nap at 2-hour intervals over the day. More than 2 SOREMPs and a mean sleep latency of less than 8 minutes strongly suggest narcolepsy. These findings are not completely specific and also can be seen in patients with severe sleep deprivation, delayed sleep phase disorder, or severe sleep apnea. For these reasons, a PSG of the previous night is necessary for interpretation of the MSLT; MSLT cannot be used alone to confirm or rule out narcolepsy.

Diagnosing narcolepsy in children presents numerous difficulties. One study found that 85% of children with narcolepsy also suffered from sleep-disordered breathing. Serial MSLTs may be required, and usually multiple confounding factors are involved (eg, increased alertness in the novel environment of the sleep laboratory). Furthermore, normative MSLT values for children have not been established.

Treatment & Management

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Author

Sagarika Nallu, MD Assistant Professor, Pediatric Neurologist and Epileptologist, Adult and Pediatric Sleep Specialist, Department of Pediatrics, University of South Florida, Morsani College of Medicine

Sagarika Nallu, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Epilepsy Society, Child Neurology Society

Disclosure: Nothing to disclose.

Chief Editor

Selim R Benbadis, MD Professor, Director of Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, Tampa General Hospital, University of South Florida Morsani College of Medicine

Selim R Benbadis, MD is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Clinical Neurophysiology Society, American Epilepsy Society, American Medical Association

Disclosure: Serve(d) as a director, officer, partner, employee, advisor, consultant or trustee for: Acorda, Cyberonics, Eisai, Lundbeck, Sunovion, UCB, Upsher-Smith<br/>Serve(d) as a speaker or a member of a speakers bureau for: Cyberonics (Livanova), Eisai, Lundbeck, Neuropace, Sunovion, UCB<br/>Received research grant from: Acorda, Cyberonics, GW, Lundbeck, Sepracor, Sunovion, UCB, Upsher-Smith.

Additional Contributors

Ali M Bozorg, MD Assistant Professor, Comprehensive Epilepsy Program, Departments of Neurology and Neurosurgery, University of South Florida College of Medicine

Ali M Bozorg, MD is a member of the following medical societies: American Academy of Neurology, American Epilepsy Society, American Academy of Sleep Medicine

Disclosure: Received honoraria from Cyberonics for speaking and teaching; Received honoraria from UCB, Inc. for speaking and teaching.

Dani J Thomas, DO Fellow in Sleep Medicine, University of South Florida College of Medicine

Dani J Thomas, DO is a member of the following medical societies: American Thoracic Society, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Acknowledgements

Carmel Armon, MD, MSc, MHS Professor of Neurology, Tufts University School of Medicine; Chief, Division of Neurology, Baystate Medical Center

Carmel Armon, MD, MSc, MHS is a member of the following medical societies: American Academy of Neurology, American Academy of Sleep Medicine, American Association of Neuromuscular and Electrodiagnostic Medicine, American Clinical Neurophysiology Society, American College of Physicians, American Epilepsy Society, American Medical Association, American Neurological Association, American Stroke Association, Massachusetts Medical Society, Movement Disorders Society, and Sigma Xi

Disclosure: Nothing to disclose.

Matthew J Baker, MD Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital

Disclosure: Nothing to disclose.

Jose E Cavazos, MD, PhD, FAAN Associate Professor with Tenure, Departments of Neurology, Pharmacology, and Physiology, University of Texas Health Science Center at San Antonio; Co-Director, South Texas Comprehensive Epilepsy Center; Director of the Epilepsy Center, Audie L Murphy Veterans Affairs Medical Center

Jose E Cavazos, MD, PhD, FAAN is a member of the following medical societies: American Academy of Neurology, American Clinical Neurophysiology Society, American Epilepsy Society, American Neurological Association, and Society for Neuroscience

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Medscape Reference Salary Employment

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