Muscle and spasticity symptoms in multiple sclerosis patients are common with the spectrum of the disease. Musculature is controlled via nerves in a person’s peripheral nervous system (PNS) which sends signals to muscles. The origin of these signals comes from the central nervous system (CNS) which encompasses the brain and spinal cord to contract a given muscle or release it.
Multiple sclerosis exacerbations (attacks) cause damage to nerves in the central nervous system known as “neurons” resulting in signal loss. The loss or misinterpretation of these signals through a network of neurons results in the symptoms associated with MS. Thus muscles may receive signals to contact but the signals to release do not come causing the muscles to spasm, jerk or become rigid.
Muscle and Tonus Overview
Nervous system pathways connect the brain, spinal cord and muscles which work together to control and coordinate movements. When signals within these pathways are misinterpreted, interrupted or weakened the muscles react accordingly. For example, when signals are interrupted the muscle may result in its shortened or contracted state making a limb feel stiff, tight difficult or even impossible to move.
If a limb becomes fixed in one position known as contracture it can result in serious implications if not promptly managed. Nerve signals disrupted can cause over or under activity in muscles as well and a loss of control and coordination leading to spasms.
Where damage occurs in the brain or spinal cord nerves has a direct correlation to where musculature control problems occur.
Muscle Tone or Tonus
In physiology, medicine, and anatomy, muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state. It helps to maintain posture for example.
If a sudden pull or stretch occurs, the body responds by automatically increasing the muscle’s tension, a reflex which helps guard against danger as well as helping to maintain balance. Such near-continuous innervation can be thought of as a “default” or “steady state” condition for muscles. There is, for the most part, no actual “rest state” insofar as activation is concerned.
Flexor muscle contraction bends a limb or other part of the body.
Extensor muscles contraction extends or straightens a limb or other part of the body.
Both the extensor and flexor muscles ( are involved in the maintenance of a constant tone while “at rest.” In skeletal muscles, this helps maintain a normal posture.
Disorders such as multiple sclerosis can result in abnormally low (hypotonia) or high (hypertonia) muscle tonus as can other conditions or injuries. In MS hyoptonia or hypertonia is caused by damage to neurons (nerve cells) resulting in loss of electrical conduction of nerve impulses known as “action potentials”.
Another form of hypertonia is paratonia, which is associated with dementia.
Hypotonia can present clinically as muscle flaccidity, where the limbs appear floppy, stretch reflex responses are decreased, and the limb’s resistance to passive movement is also decreased.
Foot drop where a individuals foot appears floppy or pointed downwards is a form of hypotonia as is facial drop often associated with stroke but can happen as well in multiple sclerosis.
Hypertonia can present clinically as either spasticity or rigidity. While spasticity is velocity-dependent resistance to passive stretch (i.e. passively moving an elbow quickly will elicit increased muscle tone, but passively moving elbow slowly may not elicit increased muscle tone).
Rigidity is velocity-independent resistance to passive stretch (i.e. there is uniform increased tone whether the elbow is passively moved quickly or slowly).
Spasticity can be in the form of the clasp-knife response, in which there is increased resistance only at the beginning or at the end of the movement. Rigidity can be of the lead pipe type, in which there is resistance throughout to passive movement, or it may be of cogwheel type, in which the resistance to passive movement is in a jerky manner.
Hypertonia may appear in limbs, fingers, toes or other parts of the body.
Paratonia or gegenhalten is defined as a form of hypertonia with an involuntary variable resistance during passive movement. In other words, attempting to move the limb of a person with paratonia will result in that person involuntarily resisting the movement. The amount of resistance is determined by the speed of the movement: faster, more forceful movements will result in greater amounts of resistance. It is also present regardless of the direction of the movement.
Dystonia is a neurological movement disorder in which sustained muscle contractions cause twisting and repetitive movements or abnormal postures. Dystonia is characterized by long-lasting (sustained) involuntary muscle contractions that may force people into abnormal positions—for example, causing the entire body, the trunk, limbs, or neck to twist. Movements are usually patterned and twisting, and may resemble a tremor.