Maximus Gage
Muscle tone is critical to several movement disorders, such as Parkinson's disease and dystonia. The main challenge is to distinguish between the main subtypes of increased muscle tone: rigidity, dystonia, and spasticity. Various scales are used to measure muscle tone, such as the Modified Ashworth Scale (MAS), which is a simple and widely used method of measuring spasticity and muscle hypertonia. The scale includes grades from 1 to 3, with 1 being a slight increase in muscle tone and 3 being a considerable increase, making passive movement difficult. Another example is the Tardieu Scale, which differentiates contracture from spasticity.
| Characteristics | Values |
|---|---|
| Slight increase in muscle tone | Catch and release, or minimal resistance at the end of the range of motion |
| Slight increase in muscle tone | Catch, followed by minimal resistance throughout the remainder (less than half) of the ROM |
| More marked increase in muscle tone | Through most of the ROM, but affected parts can be moved easily |
| Considerable increase in muscle tone | Passive movement is difficult |
| Rigidity | |
| Dystonia | |
| Spasticity | |
| Fluctuating muscle tone | Involuntary movements and limited postural stability |
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What You'll Learn
The Modified Ashworth scale (MAS)
The MAS is performed by extending the patient's limb from a position of maximal possible flexion to maximal possible extension (the point at which the first soft resistance is met). The scale is then assessed while moving from extension to flexion. The MAS is a quick and simple test that does not require any instrumentation. It is considered the current standard for clinical assessment of extremity spasticity and is the most commonly used tool to evaluate the efficacy of pharmacologic and rehabilitation interventions for the treatment and management of spasticity.
The MAS has been utilised in various populations, including stroke, spinal cord injury, multiple sclerosis, cerebral palsy, traumatic brain injury, paediatric hypertonia, and central nervous system lesions. It has been subject to criticism, however, due to its poor inter and intra-rater reliability and its inability to differentiate between the many factors that can contribute to resistance to passive stretch. Some studies have found low-average intraobserver reliability with the MAS, while others have found average-excellent scores.
The MAS grades are as follows:
Slight increase in muscle tone, manifested by a catch and release or by minimal resistance at the end of the range of motion when the affected part(s) is moved in flexion or extension.
1+. Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the ROM.
- More marked increase in muscle tone through most of the ROM, but the affected part(s) are easily moved.
- Considerable increase in muscle tone, passive movement difficult.
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Grading muscle hypertonia
The Hypertonia Assessment Tool (HAT) has been developed to aid in identifying these hypertonia subtypes. Spasticity, for instance, can be assessed by performing a slow and fast stretch of a muscle, with spasticity diagnosed if a spastic catch and increased tone are observed during the fast stretch. The Modified Tardieu Scale is another method that involves performing a muscle stretch at two velocities and measuring the angle of the spastic catch and passive range.
The Modified Ashworth Scale (MAS) is a commonly used grading scale for muscle hypertonia, particularly spasticity. It measures resistance during passive soft-tissue stretching and grades severity on a 5-point ordinal scale:
Slight increase in muscle tone, observed as a catch and release or minimal resistance at the end of the range of motion.
1+. Slight increase in muscle tone, manifested by a catch followed by minimal resistance throughout less than half of the range of motion.
- More marked increase in muscle tone throughout most of the range of motion, but the affected part can still be moved easily.
- Considerable increase in muscle tone, making passive movement difficult.
Muscle strength testing is another aspect of grading muscle hypertonia, and it involves asking the patient to contract a specific muscle group while the examiner resists the movement. Grades range from 0 (complete paralysis) to 5 (normal power), with half-grades indicating intermediate levels of strength. This method can help localise lesions and differentiate affected muscle groups to guide treatment.
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Clonic reflexes
The presence of clonic reflexes indicates a decrease in the synaptic current threshold, which enhances motor neuron excitability. This is likely due to alterations in the net inhibition of neurons caused by injury to the central nervous system. The frequency of clonic beats is directly proportional to the length of the reflex pathway it is found in.
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Rigidity, dystonia, and spasticity
Rigidity
Rigidity is a condition in which it is difficult to move the muscles through their range of motion, regardless of the speed at which the movement is attempted. This condition is often associated with severe damage to the brain. Decorticate rigidity, for example, is a sign of damage to the nerve pathway in the midbrain, which is between the brain and spinal cord.
Dystonia
Dystonia is a condition that can occur in combination with spasticity in children with cerebral palsy. It is a type of hypertonia, which is resistance to passive movement. Hypertonia is not velocity-dependent, but there is a particular type of hypertonia in which muscle spasms are increased by movement.
Spasticity
Spasticity is a velocity-dependent increase in muscle tone in response to passive movement. The faster the passive movement, the stronger the resistance. It is considered a form of sustained efferent muscular hyperactivity, dependent on the continuous supraspinal drive to the alpha motor neuron. Spasticity can be measured using the Modified Ashworth Scale (MAS), which measures resistance during passive soft-tissue stretching.
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Proper positioning for feeding and swallowing
The correct feeding position includes maintaining a neutral alignment of the head and neck, a midline orientation, and a symmetrical trunk position. Additionally, achieving a 90-degree pelvic/femoral alignment and symmetrical arm position with neutral shoulders is essential. This positioning helps to maintain a stable and balanced posture, facilitating the complex processes of feeding and swallowing.
For swallowing, the head and neck position plays a significant role. While there are limited studies on this topic, it is known that head flexion and extension can decrease the opening of the airways and esophagus, making swallowing more challenging. Specifically, neck extension should be avoided when training patients with swallowing disorders, as it causes mechanical widening of the laryngeal vestibule and narrowing of the valleculae, leading to difficulties in closing the upper esophageal sphincter.
To facilitate swallowing and prevent aspiration, a chin-tuck position is often recommended. This position makes the vallecular space wide and the airway entrance narrow, reducing the likelihood of aspiration. Additionally, the chin-tuck position decreases pharyngeal contraction, further aiding in the prevention of dysphagia. Studies have shown that swallowing while sitting with the head and neck flexed is more challenging than sitting upright.
Maintaining the correct positioning for feeding and swallowing is essential for individuals with muscle tone abnormalities. It helps to compensate for any muscle tone-related difficulties with feeding and swallowing, reducing the risk of complications such as aspiration or food falling out of the mouth due to inadequate oral motor patterns.
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Frequently asked questions
Muscle tone refers to the amount of tension or resistance to movement in a muscle during its state of relaxation.
Increased or decreased muscle tone can contribute to difficulty preserving a patent airway, compromised self-feeding skills, poor rib cage expansion, and oesophageal motility. It can also cause involuntary movements and limited postural stability.
The Modified Ashworth Scale (MAS) is one of the most widely used methods of measuring muscle tone due to its simplicity and reproducible method.
The grades are as follows:
- Grade 1: Slight increase in muscle tone, manifested by a catch and release or by minimal resistance at the end of the range of motion.
- Grade 1+: Slight increase in muscle tone, manifested by a catch, followed by minimal resistance throughout the remainder (less than half) of the range of motion.
- Grade 2: More marked increase in muscle tone through most of the range of motion, but the affected part(s) easily moved.
- Grade 3: Considerable increase in muscle tone, passive movement difficult.
Yes, another scale is the Tardieu Scale, which differentiates contracture from spasticity.
