The causes of MS-related fatigue are currently not fully understood. Theories include immune system dysfunction or problems with the central nervous system as a result of MS. A high prevalence of fatigue in people with MS may also be caused by problems related to the condition, such as sleep disturbances, pain, or medication side effects.
Disability in MS is widely measured with the Expanded Disability Status Scale, but that tool has limited consideration of fatigue. Clinically, fatigue has been difficult to define in the field of neurology. This is because fatigue is gauged by subjective perceptions or experiences, such as pain. However, research has validated measurement tools that can help clinicians better understand the severity and impact of fatigue.
Fatigue is one of the most common symptoms of MS and can take on different forms. It is a multidimensional symptom that can affect the body and mind in individual ways. Fatigue measurement scales address the following three forms of fatigue recognized by researchers:
The term “lassitude” is a particular characteristic of fatigue that is associated with MS. It is defined as severe tiredness that may occur daily despite sleeping well and can be worsened by heat and humidity. Lassitude can come on suddenly and often hinders everyday activities. It can be associated with depression in MS and is considered difficult to measure.
Many clinical tools have been developed to measure the three major forms of fatigue in MS. Fatigue scales are generally based on self-reporting by someone living with MS. Fatigue questionnaires may assess total score or subscales of physical, cognitive, or psychosocial fatigue symptoms.
The self-reporting measurement tools described below are some of the most common scales for evaluating fatigue in people with MS.
The Modified Fatigue Impact Scale (MFIS) is a questionnaire that assesses how fatigue affects everyday life. The MFIS is based on the scoring of 21 items that address physical, cognitive, and psychosocial fatigue and focuses on fatigue’s impact on daily activities.
The Fatigue Impact Scale, a 40-item questionnaire, is the basis for the MFIS. This scale evaluates how fatigue is affecting someone on the day the test is administered.
The Rochester Fatigue Diary (RFD) measures levels of fatigue each hour over the course of a day. Questions are answered on a scale of zero to 100, with higher scores indicating less severe fatigue. The RFD was designed to determine levels of severe fatigue or lassitude, rather than specific characteristics of physical, cognitive, or psychosocial fatigue.
The Fatigue Severity Scale (FSS), sometimes called Krupp’s Fatigue Severity Scale, includes nine items (seven in a shortened version). The questionnaire emphasizes the severity of physical or motor fatigue and assesses fatigue for the week before the test is administered. The FSS is also used to measure fatigue in chronic fatigue syndrome.
Doctors and researchers administer these tools to assess the ways and degree to which 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.
Fatigue measurement tools may help your doctor make specific diagnoses of fatigue that are associated with sleep disorders or depression. Correct diagnosis is important because different conditions call for different treatments. 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.
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