Narcolepsy is a rare neurological sleep disorder. In addition to type 1 and type 2 narcolepsy, there’s a type called secondary narcolepsy — or symptomatic narcolepsy. Secondary narcolepsy is caused by injury to the brain, including a hypothalamic tumor.
Whereas type 1 and type 2 narcolepsy are idiopathic (of unknown origin), secondary narcolepsy is not. The condition is caused by injuries to the brain region that helps control sleep, called the hypothalamus. Some of these injuries include:
The symptoms of secondary narcolepsy are very similar to those of type 1 and type 2 narcolepsy, including cataplexy (sudden muscle weakness) and excessive daytime sleepiness. The biggest difference is, people with secondary narcolepsy tend to sleep for at least 10 hours a day, whereas people with type 1 or type 2 narcolepsy tend to sleep the same amount as those without narcolepsy (approximately 8 hours).
Hypothalamic tumors are brain tumors that occur in a specific area of the brain known as the hypothalamus. The hypothalamus is a small region near the base of the brain, positioned above the pituitary gland and brain stem. It is largely responsible for the production of hormones within the brain and body. Tumors in or near the hypothalamus can be disruptive.
Like most tumors, the causes of hypothalamic tumors are largely unknown. The hypothalamus can be a site of many types of tumors, including gliomas — a tumor that results from abnormal growth of a type of brain cell known as a glia. But why cells such as glia begin to grow abnormally is not well understood. In one study, researchers found that most cases of hypothalamic tumor-related secondary narcolepsy were associated with tumors called craniopharyngioma (38 percent), adenoma (24 percent), and glioma (14 percent). Some of these tumors are benign (noncancerous). Others are not. Often, it is hard to tell the difference between benign and malignant (cancerous) tumors, even using a microscope. Benign or malignant, these tumors can still cause secondary narcolepsy to occur.
Researchers have discovered that dysfunction in the hypocretin (orexin) system is associated with type 1 and type 2 narcolepsy. This has led to new insights into the processes underlying secondary narcolepsy, particularly secondary narcolepsy caused by hypothalamic tumors.
It is believed that tumors in the region of the hypothalamus cause secondary narcolepsy by affecting hypocretin-1 (orexin-A) production, as hypocretin is produced in the hypothalamus. Hypocretins, especially hypocretin-1, play an important role in the regulation of sleep, likely due to the role that hypocretin-1 plays as an “on-off” switch between states of sleep and wakefulness. Levels of this brain hormone in the cerebrospinal fluid (CSF) are often low in individuals with type 1 and type 2 narcolepsy. Importantly, one study found that most cases of secondary narcolepsy (including those caused by tumors) were also associated with lower hypocretin-1 in the CSF.
Symptoms of hypothalamic tumor-associated secondary narcolepsy that are likely a result of hypocretin-1 deficiency include:
A diagnosis of secondary or symptomatic narcolepsy from a hypothalamic region tumor will likely require an MRI examination. An MRI scan can show tumors in the hypothalamus.
Treating narcolepsy-linked tumors can be difficult, but not impossible. A biopsy may be performed to determine if surgery is an option. The use of stimulants may also help address symptoms. Both surgery and stimulants appear to increase hypocretin activity.
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