Hypertonia is a condition in which there is too much muscle tone so that arms or legs, for example, are stiff and difficult to move. The term 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. Not to be confused with common thought of the term such as muscle mass.
Muscle tone is regulated by signals that travel from the brain to the nerves and tell the muscle to contract. Hypertonia happens when the regions of the brain or spinal cord that control these signals are damaged. This can occur for many reasons, such as a blow to the head, stroke, brain tumors, toxins that affect the brain, neurodegenerative processes such as in multiple sclerosis or Parkinson’s disease, or neurodevelopmental abnormalities such as in cerebral palsy.
Hypertonia often limits how easily the joints can move. If it affects the legs, walking can become stiff and people may fall because it is difficult for the body to react quickly enough to regain balance. If hypertonia is severe, it can cause a joint to become “frozen,” which doctors call a joint contracture.
Hypotonia refers to the opposite of this condition where musculature has loss of normal tone and appears to be floppy with loss of contraction. Normally, even when relaxed, muscles have a very small amount of contraction that gives them a springy feel and provides some resistance to passive movement.
Types of Hypertonia
Spasticity is a term that is often used interchangeably with hypertonia. Spasticity, however, is a particular type of hypertonia in which the muscles’ spasms are increased by movement. In this type, patients usually have exaggerated reflex responses. Spastic hypertonia involves uncontrollable muscle spasms, stiffening or straightening out of muscles, shock-like contractions of all or part of a group of muscles, and abnormal muscle tone. It is seen in disorders such as cerebral palsy, stroke, and multiple sclerosis. Spasticity is a common symptom in multiple sclerosis.
Rigidity is another type of hypertonia in which the muscles have the same amount of stiffness independent of the degree of movement. Rigidity is a severe state of hypertonia where muscle resistance occurs throughout the entire range of motion of the affected joint independent of velocity. It is frequently associated with lesions of the basal ganglia. Individuals with rigidity present with stiffness, decreased range of motion and loss of motor control.
Dystonic hypertonia often referred to as Dystonia refers to muscle resistance to passive stretching (in which a therapist gently stretches the inactive contracted muscle to a comfortable length at very low speeds of movement) and a tendency of a limb to return to a fixed involuntary (and sometimes abnormal) posture following movement.
Symptoms of Hypertonia
Spasticity may be as mild as the feeling of tightness in muscles or may be severe enough to produce painful, uncontrollable spasms of the extremities; most commonly the legs and arms. Spasticity may also create feelings of pain or tightness in and around joints, and can cause low back pain.
Adverse effects of hypertonia may include:
- Muscle stiffness, causing movements to be less precise and making certain tasks difficult to perform
- Muscle spasms, causing uncontrollable and often painful muscle contractions
- Involuntary crossing of the legs
- Muscle and joint deformities
- Muscle fatigue
- Inhibition of longitudinal muscle growth
- Inhibition of protein synthesis in muscle cells
Additional complications may exist such as:
- Urinary tract infections
- Chronic constipation
- Fever or other systemic illnesses
- Pressure sores
Causes of Hypertonia
Hypertonia is caused by upper motor neuron lesions which may result from injury, disease, or conditions that involve damage to the central nervous system. The lack of or decrease in upper motor neuron function leads to loss of inhibition with resultant hyperactivity of lower motor neurons. Different patterns of muscle weakness or hyperactivity can occur based on the location of the lesion, causing a multitude of neurological symptoms, including spasticity, rigidity, or dystonia.
Prognosis of Hypertonia
The prognosis depends upon the severity of the hypertonia and its cause. In some cases, such as cerebral palsy, the hypertonia may not change over the course of a lifetime. in other cases, the hypertonia may worsen along with the underlying disease such as multiple sclerosis. If the hypertonia is mild, it has little or no effect on a person’s health. If there is moderate hypertonia, falls or joint contractures may have an impact on a person’s health and safety. If the hypertonia is so severe that is caused immobility, potential consequences include increased bone fragility and fracture, infection, bed sores, and pneumonia and more.
Treatment of Hypertonia
There are several types of treatment available which must be evaluated on a case-by-case basis, depending on the underlying cause, age of the patient, and severity of the spasticity. Different treatments share the common goals of:
- Relieving the signs and symptoms of spasticity
- Reducing the pain and frequency of muscle contractions
- Improving gait, hygiene, activities of daily living, and ease of care
- Reducing caregiver challenges such as dressing, feeding, transport, and bathing
- Improving voluntary motor functions involving objects such as reaching for, grasping, moving, and releasing
Physical and Occupational Therapy
Physical and occupational therapy for spasticity is designed to reduce muscle tone, maintain or improve range of motion and mobility, increase strength and coordination, and improve comfort. Therapy may include stretching and strengthening exercises, temporary braces or casts, limb positioning, application of cold packs, electrical stimulation, and biofeedback.
The use of oral medications to treat spasticity may be indicated when symptoms interfere with daily functioning or with sleep. Effective medication management may require the use of two or more drugs or a combination of oral medications with another type of treatment. It is very important to work closely with a doctor to devise an individualized treatment plan. Side effects vary greatly by class of medication and patient.
- Dantrolene sodium
Botulinum Toxin (BTA / Botox) Injections
BTA, also known as Botox injections have proven effective when used in tiny amounts, by paralyzing spastic muscles. Injection sites are carefully determined based on the pattern of spasticity.
When Botox is injected into the muscle(s), the release of acetylcholine is blocked, resulting in a relaxation of overactive muscles. The injection(s) generally take effect within a few days and last about 12-16 weeks, until new nerve endings grow back and the affected muscle(s) recover. Functional benefits may last longer than this. There are limitations in the number of injections that can be administered.
The primary neurosurgical procedures to treat spasticity are intrathecal baclofen (ITB) pumps and selective dorsal rhizotomy (SDR).
Intrathecal Baclofen (ITB)
In severe cases of spasticity, baclofen can be administered through a pump that has been surgically implanted in the patient’s abdomen. By delivering baclofen directly to the spinal fluid, a much more powerful reduction in spasticity and pain can be achieved, with fewer side effects. ITB has been found to be extremely effective in treating spasticity in the lower and upper extremities.
Selective Dorsal Rhizotomy (SDR)
In SDR, the neurosurgeon cuts selective nerve roots (rhizotomy), the nerve fibers located just outside the back bone (spinal column) that send sensory messages from the muscles to the spinal cord. SDR is used to treat severe spasticity of the legs that interferes with movement or positioning. By cutting only the sensory nerve rootlets causing the spasticity, muscle stiffness is decreased, while other functions remain intact. Decreasing spasticity can improve mobility and function, and help prevent severe muscle scarring (contractures), as well as joint and bone deformities. It is utilized most effectively in patients with CP who meet specific criteria. Individuals with the following criteria are notcandidates for SDR:
- Patients who have experienced meningitis, congenital brain infection, congenital hydrocephalus unrelated to premature birth, head trauma, or familial disease
- Patients who have mixed CP with predominant rigidity or dystonia, significant athetosis, or ataxia
- Patients with severe scoliosis
- Patients who will not make functional gains after surgery
The benefits of surgery should always be weighed carefully against its risks. Randomized, controlled clinical trials have demonstrated that a large percentage of CP patients report significant reduction in spasticity and improved function after surgery. However, surgery is not an option for all cases of spasticity.