Tremor, or uncontrolled shaking, is a highly disabling symptom of multiple sclerosis which is often associated with a more advanced disease course. Tremor, an involuntary, rhythmic, muscle movement caused by repetitive contraction and relaxation of paired muscle groups, has long been recognized as a feature of MS. The French neurologist Dr. Jean-Martin Charcot (1825-1893) categorized it with nystagmus and scanning speech (Rascol, 1982).
A study published in the open-access journal Tremor and Other Hyperkinetic Movements reviewed recent advancements in the understanding of tremors in MS. The review explores the prevalence and clinical features of tremors in MS, including physical cause of tremors, and treatment methods, including surgery and/or prescription medications.
Reviewers searched MEDLINE with the terms “multiple sclerosis” and “tremor,” published between January 1966 and May 2012. My own search revealed articles dating back to 1958, and at least six additional relevant articles published since May 2012.
Prevalence of tremor in MS
Studies indicate that tremors are prevalent in 25% to 58% of the MS population. Upper limb tremor was described in 58% of 100 randomly selected MS patients from an MS specialty clinic in London (potential for selection bias); 27% with minimal tremor, 16% with mild tremor, and 15% with moderate to severe tremor (Alusi, 2001). In a community-based study of 200 MS patients in Olmsted County, Minnesota, tremor was noted in 25.5% of patients with severe tremor seen in only 3% of patients (Pittock, 2004).
Authors note that the prevalence of tremor in MS is difficult to establish because of the transient nature of MS symptoms, the lack of assessment for tremor in the EDSS, and the difficulty in distinguishing intention tremor from ataxia.
Assessment of tremor in MS
Tremor is an involuntary, repetitive, rhythmic movement of a body part. A tremor present during rest (muscle relaxation) is different than an action tremor which is produced during voluntary movement. The type of tremors seen in MS are action tremors, specifically postural tremor and/or intention tremor, often involving the arms, head, neck, and trunk. Vocal cords by also be affected.
Tremors which are not commonly seen in MS include rest tremor, task-specific tremor (such as while writing, for example), and simple kinetic tremor present during voluntary non-target-directed motions (such as opening and closing a fist). In general, movement disorders other than tremor are uncommon in MS (Labiano-Fontcuberta, 2012).
Tremor classification and severity scales have not been widely adopted in MS practice. One scale, the Fahn-Tolosa-Marin Tremor Rating Scale, was adapted and tested for reliability in a study, but not for validity. A 0-10 tremor severity scale devised by Bahn and colleagues in 1993 has been tested for validity and reliability in use with the MS population. However, it has only been used in a few clinical studies, according to review authors.