Spasticity : Classification, Diagnosis, and Management

Introduction

Spasticity is defined as hypertonia occurring in response to passive muscle stretch that meets one of two criteria: the hypertonia increases with increasing speed of muscle stretch, or the hypertonia increases beyond a certain critical angle of joint motion. Spasticity should be distinguished from rigidity, which is characterized by hypertonia that is present at very low movement speeds and does not worsen with rapid movement or movement beyond a threshold. Spasticity can be classified based on the number of limbs involved: spastic quadriplegia affects all limbs, spastic diplegia affects the lower limbs, and spastic hemiplegia affects the limbs on only one side.

Several grading schemes for spasticity and hypertonia in general have been created. The modified Ashworth scale is shown in Table 54.1 . Although this scale is the most commonly used to grade the severity of spasticity, it does not distinguish whether the hypertonia is due to spasticity, rigidity, or dystonia. Thus rather than grading spasticity per se, it instead reflects the severity of the patient's hypertonia overall. The Gross Motor Function Classification Scale (GMFCS), shown in Table 54.2 , is used in children to describe the overall functional limitations caused by spasticity, but it also does not specifically describe the spasticity itself.

Spasticity results from lesions of upper motor neurons that lead to hyperactivity of spinal motor neurons. This hyperactivity is associated with an involuntary, reflexive transition from relaxation to contraction as the stretch rate or degree of stretch reaches a threshold. In adults, it can occur as a consequence of spinal cord injury, multiple sclerosis, stroke, or other upper motor neuron lesions. In children, cerebral insults are far more common than are injuries to the spine. White matter lesions are particularly common causes among premature infants, possibly because of the sensitivity of oligodendrocyte precursors to hypoxic–ischemic insults during the third trimester. Genetic and metabolic diseases such as X-linked adrenoleukodystrophy, metachromatic leukodystrophy, and Pelizaeus-Merzbacher disease can also cause this clinical picture.

Cerebral palsy (CP) is a common cause of spasticity in children. This heterogeneous condition affects between 1.5 and 3 per 1000 live births and is characterized by abnormalities affecting movement and posture that interfere with normal activity. It can be broadly categorized into spastic and dyskinetic forms based on the predominant motor findings, although no standardized classification scheme exists. Children with spastic CP experience increases in tone that interfere with normal activity and caretaking; dyskinetic CP is characterized by abnormal patterns of involuntary motor movements. Risk factors include prematurity, low birth weight, and a host of genetic and metabolic factors.

Children presenting with signs and symptoms of CP should undergo a thorough evaluation, including assessment of developmental milestones, a general medical history, and screening for associated neurologic impairments such as epilepsy or sensory disturbances. The physical examination should focus on muscle bulk, muscle tone, posture, and, if the child is old enough, gait. Magnetic resonance imaging of the brain should be obtained to evaluate for structural abnormalities. Children with CP do not typically regress in terms of function, so loss of acquired milestones should prompt further workup and evaluation. Notably, the severity can vary with the patient's alertness and emotional state, which can complicate evaluations in young children.

Associated neurologic impairments are common. One-third of children with CP experience seizures, which are frequently challenging to treat and often require treatment with multiple medications. Developmental delay is frequently present as well, and the domains affected can differ substantially from child to child. Some children with limited verbal IQ may have normal nonverbal intelligence, and others with normal verbal IQ can have profound disability in other types of reasoning. Detailed neuropsychiatric testing should therefore be performed in all children with CP.

Signs and symptoms of CP are typically present by 1 year of age, and in more than half of cases the symptoms actually improve over time. Nonetheless, other neurologic disability, such as developmental delay and seizures, may linger.

As with other diseases caused by upper motor neuron lesions, spasticity is almost always associated with hyperreflexia, clonus, weakness, and poor motor control. Although hypertonia can cause functional issues, the associated weakness and lack of control are more likely to be the primary factors underlying disability. In fact, spasticity is to some extent an adaptive response to a decrease in control. Complete treatment of spasticity when associated with weakness can actually lead to a decline in function, such as deterioration in head or trunk control or worsened ambulation.

Not all muscle groups are affected equally. Generally speaking, flexors are more affected than extensors, adductors are more affected than abductors, and muscles of internal rotation are more affected than muscles of external rotation. The cumulative effects of hypertonia can cause problems with time. Fixed contractures can develop in muscles and tendons because of prolonged, involuntary muscle contraction, leading to shortening of the tissue and reduced range of motion. Increased stiffness due to these changes can superimpose on the rigidity due to increased muscle tone and cloud the clinical picture. In severe cases, bone and joint deformities such as hip dislocation can develop and cause significant discomfort. These soft tissue and bony changes can significantly impair mobility and complicate daily care.

Nonsurgical Management

Physical and occupational therapy are central to the care of patients with spasticity. The goal is to teach parents and caretakers skills to minimize the effects of hypertonia on daily life. Exercise can help address muscle atrophy, and stretching is used to prevent contractures, although in cases of severe hypertonia stretching may not be feasible. Adjunctive therapies such as treadmill training can help improve gait, and there is experimental evidence that transcranial stimulation can improve the response to this intervention in children via modulation of cortical activity. Direct electrical stimulation of the muscles has also been found to help improve range of motion and gait.

In patients whose spasticity interferes with function, cosmesis, or daily care, tone reduction should be considered. Botulinum toxin is a neurotoxic protein produced by Clostridium botulinum that is used for local control of spasticity. The agent is injected intramuscularly, where it is internalized by presynaptic neurons at the neuromuscular junction to prevent the release of acetylcholine. Of the seven types of botulinum toxins, types A and B have biologic activity in humans and are available commercially in the United States; of these two, type A has been studied more extensively. Botulinum toxin is highly effective. It has been shown to substantially improve spasticity in the targeted muscles, and its use also helps to alleviate pain. Several randomized trials have also demonstrated significant improvements in gait and functional status, although improved functional outcomes have not been seen universally. Functional gains appear to be more robust when injections are combined with occupational therapy. Serial casting is an effective adjunct to botulinum toxin for children with ankle equinus.

Oral medications can also be used to treat generalized spasticity. Baclofen is a gamma-amino butyric acid (GABA _B ) receptor agonist that has been shown in some studies to reduce spasticity and improve both passive and active range of motion, although high-quality evidence of improved functional outcomes is wanting. Side effects, including sedation and confusion, can be significant. Withdrawal syndromes are a risk with sudden cessation. Tizanidine is a centrally acting α ₂ -agonist that has also been used, and limited evidence suggests that it may be more effective and better tolerated than baclofen. Diazepam may also be considered.

Orthopedic Surgery

Children with severe spasticity frequently require orthopedic procedures to help address deformities. Contractures are treated with tendon-lengthening procedures to improve range of motion. Osteotomies may also be required to correct bony malalignment and restore muscle action to the desired plane. Arthrodesis is performed for progressive scoliosis to help with sitting and may be required to definitively treat hallux valgus (great toe bunion). Although these deformities may appear sequentially as the child ages, many providers now prefer to wait until the child is approximately 7 to 9 years of age before intervening. Delaying surgery allows the provider to better understand the relative contributions of dystonia and spasticity to the overall clinical picture, and it also facilitates gait analysis, which is important in operative planning. It also enables the child to mature and understand his or her condition and the reasons for surgery. These procedures should be conducted simultaneously in a single setting, an approach termed single-event multilevel surgery (SEMLS). Performing these operations together prevents the phenomenon of “birthday surgeries,” where the patient undergoes regular, nearly annual operations during development as deformities arise; this practice leads to a near constant state of recovery and rehabilitation, significantly impairing the child's ability to live a normal life. SEMLS has been shown to provide good outcomes, both in the short term and on long-term follow-up. Hip dislocations are an important exception that should be treated sooner, if they occur.

Intrathecal Baclofen