What Causes Fatigue in Multiple Sclerosis?

Primary and Secondary Causes of MS-Related Fatigue

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Fatigue is considered by many to be the worst part of multiple sclerosis, and unfortunately, affects most of those with MS. Indeed, on "bad fatigue days," it's unimaginably difficult to even meet one's basic needs, due to overwhelming tiredness that makes everything more challenging. As it turns out, MS-related fatigue is usually the product of several factors working together.

Primary Fatigue

Primary fatigue is the result of the disease process itself and is caused by demyelination in the central nervous system. "Lassitude" is often used to describe this fatigue, meaning that the overwhelming tiredness is directly related to increased activity and does not generally improve with rest or sleep. The fatigue too can be described as feeling physically weak or mentally weak -- like in a "brain fog."

This fatigue is commonly worsened when your body temperature rises -- like on a hot day or when you exercise, have a fever, or take a hot bath. The term used to describe this experience is called the Uhthoff phenomenon -- but don't fret too much if this happens. When heat worsens your fatigue, it's not a sign of a new relapse and is reversible when the heat source is removed. 

There is also something called "short-circuiting" or "localized" fatigue, where affected nerves of individual muscle groups tire with use, such as your legs after walking or your hand after writing.

Secondary Fatigue

Secondary fatigue is not caused directly by the MS itself but is usually a result of MS symptoms or trying to compensate for them.

  • Sleep disturbances are common in people with MS, due to muscles spasms, depression or anxiety, pain, the frequent need to urinate at night (nocturia) or because of side effects of medications. For instance,  corticosteroids like Solu-Medrol -- used to treat MS relapses --are notorious for causing sleep disturbances. Sleep disorders, like insomnia and restless leg syndrome, are also common in multiple sclerosis. 
  • Exertion causes fatigue in people with MS when they constantly need to compensate for symptoms like spasticity or muscle weakness, which may make it harder to walk, keep your balance or complete tasks around the house.
  • Some medications also cause fatigue as a side effect, including those taken specifically for MS. These include the disease-modifying therapies which are made from beta-interferon (Avonex, Betaseron, and Rebif), Tysabri, and Novantrone. In addition, fatigue is a side effect of some medications taken for MS symptoms such as spasticity, including Baclofen, Valium (diazepam), and Zanaflex. Medications for neuropathic pain, like Neurontin (gabapentin), or for tremor, as well as non-MS medications, like those for high blood pressure, allergies, or anxiety, can also contribute to fatigue.
  • Depression often causes people to feel overwhelmingly tired. In some people, the fatigue itself causes depression. Some of the medications used to treat depression can also cause fatigue, creating a cycle of one triggering the other, which can be difficult to break. 
  • Lack of proper nutrition also causes swings in blood sugar leading to general tiredness.
  • Infections, such as colds, flu, or urinary tract infections can cause fatigue.
  • Lack of physical fitness can greatly contribute to fatigue.

Coping with Fatigue in Multiple Sclerosis

Fatigue can be a debilitating and frustrating experience for you or your loved one. The good news is that with your MS health team, you can battle your fatigue and get some relief, although not likely cure it, with simple lifestyle strategies. These include daily exercises --like short walks or arm movements -- keeping yourself cool and practicing sleep hygiene strategies. For example, be sure you are going to bed at the same time every night and sleeping in a cold, dark room.

Other therapies like physical therapy, cognitive-behavioral therapy to reduce stress, or occupational therapy to help you organize your home and work tasks may also alleviate some fatigue.

Some people also choose to take a daily stimulant medication, like Provigil (modafinil). Or you can take it as needed, like when you want to have energy and enjoy a shopping trip with your partner. 

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Article Sources
  • Birnbaum, M.D. George. (2013). Multiple Sclerosis: Clinician’s Guide to Diagnosis and Treatment, 2nd Edition. New York, New York. Oxford University Press.
  • Multiple Sclerosis International Foundation. (2003). MS in Focus: Fatigue. Volume I.