By Alon Y. Avidan, MD, as told to Alexandra Benisek
It's important to understand that periodic leg movement disorder, quick-onset rapid eye movement (REM), cataplexy, depression, and other mental health disorders can be comorbidities in people with narcolepsy.
This means that while anyone can have one or more of these conditions, it's especially common for people with narcolepsy to have them.
The symptoms of these comorbidities might be like those of narcolepsy, which might cause someone's illness to go undiagnosed for years. Since narcolepsy can impact someone's academics, career, and social life, it's important to identify and treat it early.
We want to be able to give people the opportunity to shine and be their best. Proper treatment will allow people to live up to their maximum potential and avoid the poor quality of life and consequences of a misdiagnosis.
Disordered Rapid Eye Movement (REM)
Rapid eye movement (REM) sleep is the stage in which we dream. Everyone has REM sleep, but in people with narcolepsy, REM sleep is abnormal. It occurs so fast, you may begin to dream right after you fall asleep. In most people, it takes about 90 minutes to go into REM sleep. But people with narcolepsy often enter this stage 5 to 15 minutes after they go to bed.
In REM sleep, people often act out what's in their dream. They may move while they sleep, which indicates they may be in this stage. During sleep studies of people with narcolepsy, it's very common to see this.
For those without narcolepsy, REM sleep only occurs for a period during the sleep cycle. But for people with narcolepsy, REM sleep tends to persist and can also intrude into the daytime. That can often result in abnormal napping with dreaming.
There can also be some persistence of REM sleep when the person wakes up, which we call sleep paralysis. The muscles are paralyzed and continue to stay that way until a few minutes after you wake up.
Disordered REM sleep can also cause hypnagogic and hypnopompic hallucinations. Those are unusual or bizarre dreams that occur as the person falls asleep (hypnogogic) or when you wake up (hypnopompic).
Periodic Leg Movement Disorder
In people without narcolepsy, periodic leg movements typically occur more commonly in non-REM sleep. It's very rare to see periodic leg movements in REM sleep. But for those with the condition, periodic leg movements are more uniform. They might have them during REM and non-REM sleep.
Periodic leg movement disorder isn't a separate condition from narcolepsy. It's very common to see leg movements during a sleep study in people with narcolepsy.
One of the most important conditions that is very, very unusual to encounter outside of narcolepsy is cataplexy. This is the sudden loss of muscle tone.
When someone with narcolepsy is excited, laughs, or has strong emotion, they can temporarily lose their ability to control muscle tone. This condition is very specific to narcolepsy.
People with narcolepsy are very likely to also have mood disorders. The reason why is because the disease is so devastating. It's so draining that a person with narcolepsy is more likely to have depression than another person of the same age without the disorder. And that's interesting, because it's probably related to the fact that they're very sleepy during the day, which tends to put them at a higher risk for depression.
Another problem is that some of the symptoms of depression can be similar to the signs of narcolepsy. In fact, when narcolepsy first occurs in children or teenagers, it's very hard to tell the difference between the symptoms of narcolepsy and those of depression.
Because of this, many doctors miss young people's narcolepsy. They often think their fatigue, sleepiness, and loss of energy are from a more common condition, like depression. But oftentimes, when we look at people with narcolepsy, their main symptom is severe sleepiness, whereas depression tends to be related to fatigue.
Sleepiness and fatigue are very different. Fatigue goes along with loss of energy and lack of interest in activities, while with sleepiness from narcolepsy, there's none of that. They'll usually maintain alertness and interest during activity, but sleepiness may creep in during moments of rest.
There are other comorbid psychiatric conditions, such as bipolar disorder or schizophrenia. Some of the hallucinations that people with narcolepsy report can also occur in people with schizophrenia. But with schizophrenia, the hallucinations tend to be auditory, like hearing a sound or people speaking. Visual hallucinations are more specific to narcolepsy.
There's a subtype of narcolepsy that's categorized as a central disorder of hypersomnia. This means that the condition causes sleepiness, and the origin of the illness is the central nervous system of your brain. One specific type is Kleine Levin syndrome (KLS), which doctors often misdiagnose as bipolar disorder.
KLS has similar symptoms to bipolar disorder. People with this condition tend to sleep for long periods of time over the course of days or weeks. They also may show severe cognitive troubles, crankiness, manic behavior, or hypersexuality. In between these episodes, as in bipolar disorder, people with KLS behave normally, which can span several months with only three or four episodes a year.
We don't see a lot of substance misuse from those with narcolepsy. When doctors diagnose people, we always have to think: “Is there any other reason to help explain why the patient has these symptoms?” But substance misuse often doesn't come into the picture.
In fact, many of the drugs that people use for narcolepsy are scheduled medications, which are very potent stimulants and hypnotics. But they don't tend to abuse the drugs.
Part of the evaluation of narcolepsy requires us to rule out substance disorders, which doctors do before someone comes in for their sleep study. It's left up to the clinician whether they just perform a risk assessment or require that someone take a drug test. But regardless of their decision, it's essential to exclude the possibility that someone may misuse drugs, especially since certain drugs could produce narcolepsy-like symptoms.
The Importance of a Proper Diagnosis
Comorbidities can have similar presentations to narcolepsy, which explains why doctors often misdiagnose the disorder. There's often a decade from the start of narcolepsy symptoms until it's eventually confirmed and treated.
Doctors differentiate these conditions through clinical evaluation and through the person's medical history. If someone has had a past with depression or another comorbidity, and then they have narcolepsy, they now have two conditions that doctors need to address.
Oftentimes, one type of drug can treat more than one condition. For example, some antidepressants help with depression and cataplexy. Similarly, wake-promoting drugs for narcolepsy can also help boost energy levels of people with depression. But there are also times where some conditions co-exist and we must treat them separately.
It's important to separate, diagnose, and treat narcolepsy and its comorbidities. Without correct care, people could miss out on essential accommodations or be at risk for accidents. Through a proper treatment program, I think we make a huge difference. We improve the quality of people's lives and allow them to do well for themselves.