Between 75 percent and 87 percent of people with multiple sclerosis (MS) report experiencing fatigue — and two-thirds consider it one of their worst symptoms. Unlike ordinary tiredness or sleepiness, MS fatigue is an intense form of physical and mental exhaustion. It can severely impact daily life, motivation, work ability, exercise routines, adherence to MS treatments, and personal relationships. Given that MS often strikes in young adulthood, fatigue can significantly affect someone’s prime years and quality of life.

Unfortunately, the exact cause of MS-related fatigue remains unclear, posing a challenge for doctors in measuring and treating it. In general, fatigue is hard to measure because it’s based on someone’s personal perception and individual experience. As such, most tools depend on self-reporting, which can be inconsistent.

There's still a long way to go in finding objective and reliable methods for measuring fatigue. However, researchers have validated several measurement tools that provide a good starting point for understanding and managing fatigue.

Different Forms of MS-Related Fatigue

Fatigue is one of the most common symptoms of MS and can take on different forms. MS-related fatigue is usually categorized into one of three types:

• Physical fatigue — Causes muscle weakness, muscle spasms, spasticity, and other symptoms that impair physical activity
• Cognitive fatigue — Affects attention, thinking, memory, and other cognitive functions
• Psychosocial fatigue — Reduces the desire to go out or connect with people

The term “lassitude” describes a particular type of fatigue associated with MS. Lassitude is defined as severe fatigue that may occur daily despite sleeping well and can get worse with heat and humidity. Lassitude can come on suddenly and hinder everyday activities, which sometimes leads to depression.

Potential Causes of Fatigue With MS

It’s not exactly clear why fatigue is so common with MS, but there may be more than one issue contributing to the problem. There are two main types of fatigue associated with MS — primary fatigue and secondary fatigue.

Primary fatigue describes fatigue that happens directly from MS. One theory is that demyelination and the loss of axons in the central nervous system may be responsible for this fatigue. In MS, the immune system attacks the protective myelin sheath covering nerve fibers, leading to communication problems between the brain and the rest of the body. This process can increase the brain’s effort to send signals, resulting in fatigue. Additionally, immune system changes and inflammation in MS could contribute to feelings of tiredness.

Secondary fatigue in MS stems from other MS symptoms or comorbidities. This can include anemia (low red blood cell count), which reduces the body’s ability to carry oxygen, leading to feelings of exhaustion. Additionally, some people with MS may experience sleep disturbances, leaving them feeling more tired during the day. Factors such as posture and gait changes, pain, or muscle spasms can also lead to physical and mental fatigue. Finally, some MS medications can cause fatigue as a side effect, further complicating the experience of those with the condition.

Fatigue Measurement Tools

Many clinical tools have been developed to measure physical, cognitive, and psychosocial fatigue in MS. Fatigue scales are generally based on self-reporting by someone living with MS. Fatigue questionnaires may assess total scores or subscales of different fatigue symptoms.

There are more than 250 different ways to measure fatigue. Following are some of the popular self-reporting tools that health care providers may use to assess fatigue in MS.

Modified Fatigue Impact Scale

The Modified Fatigue Impact Scale (MFIS) is a questionnaire that assesses how fatigue affects everyday life based on past interviews and research on people with MS. The MFIS includes the scoring of 21 items that address physical, cognitive, and psychosocial fatigue. It focuses on fatigue’s impact on daily activities. Some studies suggest that this is one of the most reliable ways to measure fatigue.

When taking the MFIS, a person responds to a series of statements designed to assess the impact of fatigue on their daily life. Each statement is rated on a scale from 0 to 4, where 0 means “never” and 4 means “almost always,” indicating how frequently fatigue affects them. Some examples of statements on the MFIS include:

• “I have been less alert.”
• “I have had difficulty paying attention for long periods of time.”
• “I have been clumsy and uncoordinated.”

Higher scores indicate greater impact of fatigue on a person's daily life.

The MFIS typically takes about five to 10 minutes to complete, but there is an abbreviated version that can be done in just two to three minutes, containing only five items. The MFIS was designed for self-administration, though it can also be conducted as an interview.

Fatigue Impact Scale

The Fatigue Impact Scale (FIS) is a comprehensive 40-item questionnaire used to assess a person’s current state of fatigue. It serves as the foundation for the Modified Fatigue Impact Scale.

Like the MFIS, the FIS evaluates fatigue's impact across cognitive, physical, and psychosocial functioning. This makes it a valuable tool for individuals with multiple sclerosis and also other types of chronic conditions or infectious diseases, such as hepatitis C. Respondents rate each item on a scale from 0 (“no problem”) to 4 (“extreme problem”), reflecting how significantly fatigue affects them on that day.

Examples of the types of items mentioned on the FIS include:

• “Because of fatigue, I feel less alert.”
• “Because of fatigue, I have to reduce my workload or activities.”
• “Because of fatigue, I feel slowed down in my thinking.”

Although the FIS is an extensive tool providing detailed insights, its length can be challenging for someone experiencing significant fatigue to complete. This is where shortened versions, like the MFIS and abbreviated MFIS, become particularly useful. They offer a more manageable approach to assessing fatigue without sacrificing the depth of information needed for effective treatment planning.

Rochester Fatigue Diary

The Rochester Fatigue Diary measures levels of fatigue over the course of a day. It’s one page with 24 vertical bars. People with MS rate their level of fatigue once every hour by marking a point from 0 (max fatigue) to 100 (no fatigue).

Fatigue Severity Scale

The Fatigue Severity Scale (FSS), also known as Krupp’s Fatigue Severity Scale, is a reliable self-reported measure designed to assess fatigue. The FSS consists of nine items, with a shortened version available that includes seven items. One item refers to cognitive fatigue, while the rest focus on physical fatigue. Respondents rate each item on a scale of 1 to 7, where 1 means complete disagreement and 7 indicates complete agreement.

Along with the MFIS, the FSS is considered by some experts to be one of the best ways to measure fatigue severity. It’s relatively quick and inexpensive to use.

Why Measuring Fatigue Matters

Fatigue is the most common symptom of MS interfering with day-to-day activity. Doctors and researchers use these tools to see how fatigue affects people with MS. These measures can be used in studies to help researchers learn whether specific treatments, therapies, or interventions are effective in improving fatigue and its impact on daily life.

Tools for the assessment of fatigue may help your doctor make specific diagnoses of fatigue that are associated with sleep disorders or depression. Correct diagnosis is important because different clinical presentations call for different management measures. Measurement scales can also help evaluate the level of fatigue that may persist during or after treatment.

Researchers continue to seek more precise methods for analyzing and applying outcome measures of fatigue to health care policy and clinical practice guidelines.

Talk With Others Who Understand

MyMSTeam is the social network for people with multiple sclerosis and their loved ones. On MyMSTeam, more than 214,000 members come together to ask questions, give advice, and share their stories with others who understand life with MS.

Have you ever taken one of these assessments of fatigue tools? What is the impact of fatigue on your life with MS? Share your experience in the comments below, or start a conversation by posting on your Activities page.