Narcolepsy, a type of sleep disorder, occurs in about 1 in 2,000 people in the United States. Rarely, narcolepsy can be caused by tumors and brain injuries. When narcolepsy occurs due to another illness or head injury, it’s called secondary narcolepsy. Unlike primary narcolepsy, secondary narcolepsy frequently occurs without any genetic factors.
In general, narcolepsy is caused by the dysfunction of neurons (brain cells) that secrete hypocretin. Hypocretin is a messenger molecule in your brain that is involved in wakefulness and appetite. Neurons that secrete hypocretin are only found in your hypothalamus. The hypothalamus is a region of your brain near its center. It is involved in your emotions, hunger, thirst, sleep, and other functions. These cells also have long, wire-like connections that extend throughout other parts of your brain.
A 2018 University of Copenhagen study of 72 people — 20 of whom had previously been diagnosed with narcolepsy — concluded that the condition is likely caused by autoimmune disease. (If a person has an autoimmune disease, their immune system mistakes their healthy tissue for disease-causing viruses or bacteria.) In typical narcolepsy cases, a person’s autoimmune response targets hypocretin-secreting cells and destroys them. Genetic factors, such as certain inherited genes, and environmental exposures, including certain infections (like strep throat), can increase a person’s risk of developing narcolepsy.
However, anything that damages these neurons or their connections can lead to narcolepsy. That leaves the door open for a person to have a case of secondary narcolepsy. Secondary narcolepsy can develop due to masses in the brain (such as tumors), or injuries (such as traumatic brain injury). Damage can also be caused by stroke or when a person has other autoimmune disorders that attack neurons.
Causes of secondary narcolepsy can include:
Aside from the cause, secondary narcolepsy is similar to other types of narcolepsy in terms of its symptoms, diagnosis, and treatment.
The symptoms of secondary narcolepsy are the same as other types of narcolepsy. It can occur with or without cataplexy (an immediate weakening — or loss of power — in your muscles).
There is, however, one symptom that is unique to secondary narcolepsy. People with secondary narcolepsy tend to sleep for 10 hours or more at night — a symptom called hypersomnia.
Other neurological symptoms may also occur, depending on the extent of damage to a person’s brain. Those symptoms include:
To get an accurate diagnosis of the type of narcolepsy you may have, you will need to have sleep studies. An overnight sleep study (polysomnogram) records your brain activity as you sleep. A multiple sleep latency test (MSLT) helps your doctor assess your sleep during daytime. These tests help identify abnormal sleep patterns and disordered rapid eye movement (REM) sleep. The studies can also identify sleep apnea — a separate condition that can also lead to daytime sleepiness.
Laboratory tests for hypocretin levels in your cerebrospinal fluid (fluid surrounding the brain and spinal cord) may be used for your diagnosis, too. Obtaining this fluid requires a lumbar puncture, also called a spinal tap. Knowing your hypocretin levels can help your doctor determine the best treatment for your specific case.
When secondary narcolepsy is diagnosed, it is important to identify its cause. Imaging, including computed tomography (CT), may be used to look for evidence of head trauma. A magnetic resonance imaging (MRI) scan may be needed to identify damaged areas of your brain. (MRI can see details of soft tissue, such as the brain, that X-rays and CT cannot.)
Narcolepsy without cataplexy (type 2 narcolepsy) can be treated with drugs such as Sunosi (solriamfetol), Provigil (modafinil), and Nuvigil (armodafinil). Stimulants such as Adderall (amphetamine/dextroamphetamine) and Ritalin (methylphenidate hydrochloride) can be used for treatment, as can antidepressant medications.
On MyNarcolepsyTeam, the social network for people with narcolepsy and their loved ones, more than 8,000 members come together to ask questions, give advice, and share their stories with others who understand life with narcolepsy.
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