Injury to the brain or spinal cord: what is meant by spasticity?

By Cristiano Antonino Last updated Jun 17, 2023

From the Greek spasmos (‘cramp’), the word ‘spasticity’ indicates a disproportionate increase in muscle tone, and is a clinical sign caused by an injury to the encephalon or spinal cord

Spasticity is caused by injuries, from a variety of causes, to the first-order motion neurons, i.e. those nerve cells that – from the area of the cerebral cortex deputed to movement – transmit the nerve impulse intended for muscle contraction.

According to data from the SINCH (Italian Society of Neurosurgery), spasticity affects 12 million people worldwide.

Eighty per cent of patients with paresis or plegia suffer from spasticity, although the levels of severity can vary widely.

Similarly, 80% of people with multiple sclerosis suffer from it.

But there are several causes that can lead to the onset of this condition.

Spasticity, what it is

Spasticity is a potentially disabling condition in which there is an increase in muscle tone at rest, and resistance to passive mobilisation.

The muscles, therefore, are never completely relaxed, may be rigid or tense, and may impair normal movement, speech and walking.

Spasticity is due to a combination of paralysis, hypertonus and increased activity of the spinal reflex arches, due to disinhibition from central inhibitory afferents.

This is how Lance defined it in 1980: ‘Spasticity is a motor disorder characterised by a velocity-dependent increase in the tonic stretch reflex (muscle tone) with exaggerated tendon jerks, resulting from hyperexcitability of the stretch reflex, as one of the components of the upper motor neuron syndrome’.

While, in 2003, a team of American experts redefined it as ‘a speed-dependent increase in hypertone, with a jerk when a certain threshold is exceeded’.

The resistance to passive movement that occurs in spasticity, in fact, is dependent on the speed at which this mobilisation is carried out: moving a spastic limb at a low speed will result in low resistance, while moving it faster will increase resistance.

The ‘jack-knife phenomenon’ is also typical: that is, after an initial resistance to movement, there is a sudden muscle relaxation, which then allows passive stretching.

Often, spasticity is accompanied by other signs of first-order motor neuron injury, i.e. paralysis involving mainly voluntary movements, increased osteotendin reflexes and, in some cases, clonus.

Often, behind the spasticity, there are severe pathologies

cerebral palsy
multiple sclerosis
cerebral stroke
spinal cord injury

Cerebral palsy is a condition that has been present since birth, due to hypoxic-ischemic impairment of various areas of the brain, particularly the areas responsible for controlling muscle tone and movement.

There are often associated osteo-articular deformities, not congenital but secondary to tendon retractions and muscle contractures due to paralysis and spasticity

Other conditions are acquired.

Stroke, whether ischaemic or haemorrhagic, usually occurs in middle-aged patients with cardiovascular risk factors such as hypertension, diabetes, arrhythmias, and involves several cerebral areas in a defined pattern, which follows the vascular territories.

Stroke generally affects only one hemisphere, so the motor deficit involves only one side of the body.

It may then be associated with other unilateral disorders, such as visual field disorders, or sensory deficits, or, if it involves the dominant hemisphere, with speech disturbance (aphasia).

Very often, spasticity instead indicates the presence of multiple sclerosis.

Multiple sclerosis is more frequent in women, usually begins at a younger age than stroke, and may be associated with other disorders such as sphincter incontinence, visual disturbances in a single eye, paresthesias, fatigability.

Finally, pathologies of the spinal cord, which affect the axons of motor neurons in their descending course, can also give paresis and spasticity: in this case, the disorders are localised below the level of the lesion, may be bilateral and are almost always accompanied by other deficits such as flaccid paralysis at the level of the lesion, disturbances in sensitivity and sphincter disturbances.

Other causes may be:

meningitis
encephalitis
post-traumatic brain injury
cerebral anoxia
amyotrophic lateral sclerosis
leukodystrophies (e.g. adrenoleukodystrophy, a serious genetic degenerative disease affecting the nervous system and certain endocrine glands)
hereditary spastic paraparesis
phenylketonuria (a disease of amino acid metabolism that causes mental retardation)

Spasticity: what symptoms does it manifest itself with?

Spasticity is itself a symptom: the patient may experience mild muscle tension or uncontrolled spasms of the legs and arms.

Often the spasm is accompanied by joint pain, up to and including low back pain.

Other typical symptoms are:

muscle weakness
muscle rigidity (movements become imprecise and difficult)
muscle and limb deformities

Spasticity is often associated with muscle weakness, which can result in paresis (difficulty in performing certain movements) or complete plegia (complete inability to move the affected limb).

One speaks in this case of

monoparesis, if the motor deficit affects only one limb
paraparesis, if the motor deficit affects both legs
hemiparesis, if the motor deficit affects only one side of the body
tetraparesis, if the motor deficit affects all four limbs and sometimes also the muscles of the trunk and neck

Depending on the different brain areas affected by the underlying pathology, the patient may experience

balance disorders
difficulty swallowing
chronic constipation
urinary tract infections
bedsores
ataxia (disorder consisting of progressive loss of muscle coordination)
dysarthria (speech disorders caused by a lack of control of the muscles that enable articulation)
tendon shortening
muscle retractions

How is spasticity diagnosed?

The neurological specialist, in order to make his diagnosis of spasticity, will assess the strength when performing certain movements and the resistance of the muscle to passive stretching.

In addition, he/she will observe the presence of associated signs and symptoms, e.g. the appearance of pathological and primitive reflexes.

The most typical is Babinski’s sign, an abnormal response to the plantar skin reflex.

To complete the diagnosis, the Ashworth scale is now used, which assigns a score between 0 and 4 to alterations in muscle tone:

0: no change in muscle tone occurs during mobilisation;
1: moderate increase in tone, with a “stepping” sensation when the limb is flexed and extended;
2: noticeable increase in tone, but with mobilisation still possible;
3: significant increase in tone, with difficult passive movement;
4: fixed contracture in flexion or extension.

It is essential that spasticity is detected and diagnosed early, so that the specialist can get to the bottom of the symptom and discover its causes: only with a correct diagnosis is it possible to study the right treatment that can improve the patient’s quality of life as much as possible.

Spasticity: treatments

Treating spasticity is fundamental to improving a person’s quality of life.

The typical approach involves the use of various therapeutic techniques, with a combination of drugs and physiotherapy treatments: the aim of the former is to reduce pain and hypertonus, the aim of the latter is to strengthen healthy muscles and mobilise those affected by spasticity.

The drugs used to treat spasticity are:

diazepam, a benzodiazepine used to relax spastic muscles. It can, however, give a feeling of drowsiness and reduce alertness, although these effects usually tend to wear off over time;
baclofen, a muscle relaxant that acts as a GABA-B receptor agonist. It can be administered either orally or intrathecally by surgically implanting a subcutaneous infusion pump and catheter that releases the drug at predefined intervals. Dizziness, psychological disturbances, weakness and a sense of sedation may be experienced;
tizanidine, a muscle relaxant drug that is an agonist of presynaptic alpha2adrenergic receptors. Side effects include dizziness, a sense of sedation, muscle weakness, hypotension and bradycardia.

Other treatments for spasticity include

injections of botulinum toxin into affected muscles, which block transmission at the neuromuscular junction, thereby reducing the excitatory action of the second-order motor neuron on the muscle;
physical and occupational therapy, designed to reduce muscle tone, maintain or improve range of motion, and increase strength and coordination. It may consist of: stretching, muscle strengthening, use of braces or temporary casts, cold packs, electrical stimulation, passive physiokinesitherapy;
selective dorsal rhizotomy, a surgical procedure that consists of selectively cutting the sensitive nerve roots (nerve fibres that send sensory messages from the muscles to the spinal cord): muscle stiffness decreases, while other functions remain intact. However, the operation cannot be performed in patients with mixed cerebral palsy with predominant rigidity or dystonia, meningitis, congenital hydrocephalus or congenital brain infection, patients with severe scoliosis and for whom functional recovery after surgery is not expected. It is currently little used.

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