Muscular weakness is a common complaint in many conditions, including fibromyalgia. It can also result from vitamin D deficiency, or occur following a stroke or injury to a nerve. Muscle weakness can occur due to low levels of sodium or potassium in the blood, and is also a common side effect of major neuromuscular conditions, such as cerebral palsy or multiple sclerosis. One study has suggested that a rare (and recently discovered) genetic disorder known as myotonic dystrophy type 2 (DM2) often presents with symptoms similar to fibromyalgia, including muscle weakness, muscle pain, and joint stiffness. Auvinen et al. noticed that several of their patients who carried the genetic mutation associated with DM2 had a previous diagnosis of fibromyalgia. In turn, they conducted a study to determine if some DM2 patients are erroneously diagnosed as having fibromyalgia. The researchers randomly selected 90 fibromyalgia patients who then underwent genetic testing to determine if they had the DM2 mutation. Although only 3.2% (2 patients) were found to have the DM2 mutation, the authors suggest that DM2 should be investigated in larger groups of patients, and that doctors should be aware of the fact that the symptoms for both DM2 and fibromyalgia often overlap (Auvinen et al., 2008).
In general, muscle weakness is difficult to study in that it can be either subjective or objective. An example of subjective muscle weakness would be a situation in which an individual feels weak, but has no real loss of strength, such as during a bout with the flu. Objective muscle weakness means that there is an actual loss of strength that can be verified upon physical examination. In the case of fibromyalgia, it is possible that objective muscle weakness may be related to the condition itself; however, it likely arises as a result of muscle under-use due to decreased mobility and physical activity. Subjective muscle weakness may also result from the widespread fatigue, pain, and stiffness that are characteristic of fibromyalgia.
Fibromyalgia patients can benefit from detailed tracking of their symptoms in order to gain a better understand of when and why their muscle weakness occurs. Important specifics to note while tracking muscle weakness include the following: time pattern of the muscle weakness (i.e., when it began, if it followed a vaccination or new medication, is it worse at a particular time of day, etc.); quality of the muscle weakness (i.e., is it constant or fleeting, is it made worse by specific activities, is there pain, numbness, or tingling associated, etc.); the location of the weakness (i.e., is it generalized or limited to a specific area); exacerbating and relieving factors (i.e., what makes the weakness worse or better, etc.); and are there any accompanying symptoms (i.e., did any other symptoms occur when the weakness first appeared, do any others accompany it during flare-ups, etc.).
Due to its nonspecific nature, the research related to muscle weakness and fibromyalgia is sparse. Many studies note that it is a common symptom, however most do not delineate if they are referring to objective or subjective findings. There are a few exceptions, however. Henriksen et al. demonstrated that fibromyalgia patients experience significantly reduced knee muscle strength; however, they noted that this decrease in strength is not usually related to other symptoms (Henriksen et al., 2009). A 2009 study by Watson et al. evaluated various neurological signs and symptoms in 166 fibromyalgia patients and 66 control subjects. Out of a variety of symptoms surveyed, the researchers found that 58% of fibromyalgia patients reported “weakness” in the arms and legs (i.e., subjective weakness), versus only 2% of the control subjects. Watson and colleagues later correlated these subjective findings to objective measures of both muscle strength and muscle atrophy (wasting away; decrease in mass); however, they did not state what those objective measures were (Watson et al., 2009).
An area of research that is indirectly related to muscle weakness (but of great importance to fibromyalgia patients who are searching for the most comprehensive and effective means of treatment) is strength training. Considerable evidence suggests that regular, moderately intense exercise is an integral part of a comprehensive fibromyalgia treatment plan. Despite the fact that studies differ in their recommendations as to which mode of exercise is the most useful, the majority suggest that a combination of aerobic exercise and strength training are the most effective (Panton et al., 2009; Geel & Robergs, 2002; Hakkinen et al., 2002; Gowans et al., 2001; Valkeinen et al., 2006). Strength training involves the use of force applied to a muscle or muscle group, which over time increases the strength of the muscle(s). Please refer to our article on strength training for complete information relative to strength training as a treatment tool for fibromyalgia.