Thomas Scammell, MD, discussed diagnostic challenges and solutions in a symposium during the SLEEP 2016 meeting.
Symptoms of Narcolepsy
Typical symptoms of narcolepsy include excessive daytime sleepiness (EDS), cataplexy, and other REM sleep-like phenomenon such as sleep paralysis and hypnagogic and hypnopompic hallucinations, said Thomas Scammell, MD, a professor of neurology at Harvard Medical School, during the “Best Practices for Managing Narcolepsy and Obstructive Sleep Apnea: Evidence-Based Strategies and Solutions” symposia on June 13 in Denver. In an e-mail interview with Sleep Review, Scammell, also employed at Beth Israel Deaconess Medical Center and Boston Children’s Hospital, said, “All patients have sleepiness, and each of the other symptoms are seen in roughly half of patients. Overweight, depression, and other concurrent sleep disorders such as obstructive sleep apnea are also common in people with narcolepsy.”
Cataplexy is defined as brief episodes of muscle weakness, triggered by strong emotions such as laughter or anger. Dependent on the person, Scammell noted that the frequency of cataplexy can vary from only one episode each year to several per day. Consciousness is preserved during cataplexy; partial cataplexy can affect only the face, voice, or a limb.
Causes of Narcolepsy
“Severe loss of the hypocretin neurons is the only known cause of narcolepsy,” Scammell said. “This appears to be the usual cause in narcolepsy type 1 (NT1), but the cause of narcolepsy type 2 (NT2) is unknown.” He said NT2 is difficult to diagnose because CSF hypocretin is typically normal in this type of narcolepsy, so there is no specific biomarker. As such, clinicians must rely on the multiple sleep latency test (MSLT) and clinical history of the patient.
“The challenge is that many other disorders can produce chronic sleepiness, and the MSLT can be falsely positive or falsely negative,” Scammell said. (See “Ensuring Optimal Conditions for MSLT Helps Establish Strong Narcolepsy Diagnosis.”)
Establishing a Strong Diagnosis
In order to more accurately diagnose narcolepsy, Scammell said that healthcare providers should rule out other causes of EDS, such as obstructive sleep apnea, shift work, and insufficient sleep. A detailed patient history can also aid in diagnosis. Also, the provider should make certain the patient has cataplexy by asking whether there is true muscle weakness as opposed to just a feeling of weakness, whether the episodes are brief, and if there are clear emotional triggers for the episodes, he said.
In addition, the frequency of REM phenomena can be assessed; for example, in people with narcolepsy, hallucinations of sleep paralysis often occur several times per month; these symptoms can also occur in otherwise healthy people, but usually only a few times over several years.
Finally, providers can consider measuring cerebrospinal fluid (CSF) Hcrt in patients with atypical cataplexy or those with suspected narcolepsy with cataplexy in whom MSLT is impractical, Scammell said. He also recommended adhering to the aforementioned suggestions and knowing the appropriate American Academy of Sleep Medicine guidelines for performing the PSG and the MSLT.
The symposium was sponsored by Voxmedia and supported by an independent educational grant from Jazz Pharmaceuticals.
Cassandra Perez is associate editor for Sleep Review. CONTACT [email protected]