Narcolepsy is a rare sleep disorder marked by excessive daytime sleepiness (hypersomnia), sleep attacks, sleep paralysis, and, in some cases, cataplexy. Multiple sclerosis (MS) is a neurodegenerative disorder that can cause motor disturbances. Both of these disorders are autoimmune diseases.

Both narcolepsy and MS can occur in the same person, at the same time. When this co-occurrence of disorders happens, it is called comorbidity. Living with comorbid narcolepsy and MS presents its own set of difficulties, but understanding what these disorders have in common can be useful in managing symptoms.

Narcolepsy and MS Comorbidity

Generally, sleep disorders commonly occur in those with MS. Examples of such sleep disorders include insomnia, restless legs syndrome, and obstructive sleep apnea. Although it is a rare combination, narcolepsy and MS can also be comorbid. One systematic review analyzed two studies that reported instances of comorbid narcolepsy and MS. This review found rates of people with both conditions ranging between 0 percent and 1.2 percent. An underdiagnosis of sleep disorders in people with MS may play a role in this lack of data.

Doctors may overlook symptoms of narcolepsy in people with MS. One Japanese study demonstrated — in a small case study — that among seven individuals who had MS and excessive daytime sleepiness, four met diagnostic criteria for narcolepsy upon further inspection. In addition, they had hypothalamus lesions and hypocretin (orexin) deficiency, two critical biological features of narcolepsy.

Shared Risk Factors

This comorbidity may be due, in part, to the autoimmune component of MS and narcolepsy. Genetic susceptibility is also believed to play a role. These factors were demonstrated by research that came soon after the 2009 H1N1 swine flu pandemic. In a few European countries, a vaccine known as Pandemrix was distributed, and a larger than normal proportion of children developed narcolepsy. More recent research suggests that the link between the Pandemrix vaccine and narcolepsy is likely due to immune cells (T cells), which were primed by H1N1 vaccine peptides, cross-reacting with autoantigens found within the central nervous system (brain and spinal cord). The Pandemrix vaccine essentially caused the body of a genetically susceptible individual to attack itself.

In the context of MS, one study showed that a genetically susceptible man with MS received the same vaccination during the 2009 pandemic and subsequently developed narcolepsy. This genetic susceptibility centers on the HLA (human leukocyte antigen) gene. The man had both the HLA DRB1*15:01 allele (associated with MS) and the HLA DQB1*06:02 allele (associated with narcolepsy). Thus, HLA gene variants were speculated to be a shared risk factor for narcolepsy and MS.

Shared Symptoms

Narcolepsy and MS also have a few shared symptoms. For instance, fatigue is widely experienced by both people with narcolepsy and those with MS. Fatigue is also associated with symptoms of depression and a reduced quality of life. Sleepiness, while less common than fatigue in cases of MS, is also experienced by people with both conditions.

Hypothalamus lesions can occur in both narcolepsy and MS. The main difference is that brain lesions are specific to the hypothalamus in cases of narcolepsy. In cases of MS, these lesions spread throughout the whole brain as myelin is destroyed (a characteristic MS symptom). People can even develop secondary narcolepsy via damage to the hypothalamus.

Treatments for Narcolepsy and MS

If a person is living with narcolepsy and MS, treatments may include approaches that work to curb dysfunction associated with each condition. There are also some common treatments — this is largely because several side effects of narcolepsy and MS are the same. Sometimes the same drug can be used to treat different (but similar) symptoms. For instance, Provigil (modafinil) is used to treat fatigue in MS and excessive daytime sleepiness in narcolepsy.

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