Last updated Jan. 17, 2022, by Marisa Wexler, MS ✅ Fact-checked by Ines Martins, PhD Multiple sclerosis (MS) is a disease in which the immune system erroneously attacks the nervous system, which can interfere with the normal communication between nerves and muscles. The nervous system — the brain, spinal cord, and the network of nerves that run throughout the body — is vital for coordinating muscle movement. As a consequence of MS damage, many people with MS experience muscle spasms or spasticity. A muscle spasm is a sudden, involuntary tightening or contraction of the muscle, which may cause a limb to kick out or jerk in an uncontrolled manner. Spasticity refers to muscles being abnormally tight over time, which can make it hard to move and result in feelings of stiffness, heaviness, and/or pain. These symptoms may be aggravated by sudden movements, very hot or cold temperatures, humidity, infections, or particularly tight clothing. Spasticity and its spasms can affect any part of the body, but it is especially common for people with MS in the legs and hips. Spasms in the limbs may be classified as “flexor” if they cause a limb to bend and make it difficult to straighten, or as “extensor” if they cause a limb to straighten and so rigid it’s hard to bend. The severity of these symptoms varies substantially person-to-person, and also tends to change over time, even throughout the day. Spasticity and spasms can make it difficult to walk or perform daily tasks, and also can increase the risk of falls. However, some amount of spasticity also can be beneficial in some instances, like when helping people with significant muscle weakness to keep the legs straight when they stand or move about. It is estimated that as many as 90% of MS patients will experience some form of spasticity or spasms at some point in the course of their disease. Management of these symptoms is tailored based on the needs of the individual patient, and generally involves medications alongside physical and occupational therapy. Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis, or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.