Introduction
Spasticity is a motor disorder marked by a velocity-dependent increase in muscle tone or tonic stretch reflexes associated with hypertonia.[1]
Colloquially, it is often referred to as “tightness” or “stiffness.” Spasticity can present variably in a clinical setting, sometimes with a subtle neurological manifestation and, other times, with severely increased muscle tone leading to immobility of joints.[2] Spasticity can lead to many complications, including but not limited to, interference with daily function, hygiene, comfort, and nursing care as well as contractures, increasing the risk of pressure ulcers and subsequent infections. Also, spasticity poses an increased risk of subluxation and/or dislocation as well as heterotopic ossification.[3] However, spasticity can prove to be beneficial for some patients, allowing them to ambulate or simply stand/bear weight, which in turn decreases their risk of developing osteoporosis, aids in improved circulation, and improves overall mental health. [4]
History and Physical
A patient may present with new-onset spasticity after suffering from a stroke, SCI, or TBI. On the other hand, they may have been diagnosed with MS years ago or have had CP since infancy and present with new or worsening of pre-existing spasticity. On physical exam, hallmark findings include high muscle tone in muscle groups such as the shoulder adductors; elbow, wrist, and finger flexors; and forearm pronators.[8] A characteristic finding in the hand includes a “thumb in palm” deformity, where excessive finger flexion and adduction of the thumb results in a clenched fist, with fingers wrapping around the thumb. In the lower extremities, the increased tone is especially prominent in the hip adductors, knee flexors and extensors, and plantar flexors and invertors of the ankle. Patients may report difficulty with footwear if their spasticity involves constant, high tone of the extensor hallucis longus or long toe flexors. On physical exam, the clinician will notice that spasticity varies with the speed of movement; meaning the faster the muscle is moved or stretched, the greater the resistance to stretch or passive elongation is felt. Additional physical exam findings include clonus, spastic co-contractions, and spastic dystonia. Clonus is defined as an alternating muscle contraction and relaxation of the agonist and antagonist muscles. Spastic co-contractions are abnormal antagonist contractions that present during voluntary agonist effort. Spastic dystonia is a muscle contraction that is present at rest, leading to a constant clinical posture that is highly sensitive to stretch.
Spasticity is frequently graded using the modified Ashworth scale, which is graded 0 to 4.[3][4][3] Other commonly used scales include the Tardieu scale and Penn spasm frequency scale.[9][4]
Ashworth Scale
- Zero is defined as no increase in tone.
- 1 is a “catch and release,” or minimal resistance towards end-of-range of motion (ROM).
- 1+ is similar to a grade of 1, but with a catch that is followed by resistance through less than half of ROM.
- 2 is increased muscle tone through the majority of ROM while still able to move the affected part.
- 3 is difficult passive movement throughout the majority of ROM.
- 4 presents with the affected part in rigid flexion or extension.
Tardieu Scale
- Velocity to stretch is graded from V1 (as slow as possible) to V3 (as fast as possible).
- Muscle reaction is graded from 0 (no resistance through passive movement) to 5 (joint being immobile).
- The spasticity angle is graded as R1 (angle of catch at velocity V2 or 3) or R2 (full range of motion when the muscle is at rest and tested at V1 velocity).
Penn Spasm Frequency Scale
- 0 is no spasms.
- 1 is no spontaneous spasms; only elicited through vigorous sensory and motor stimulation.
- 2 is occasional spontaneous spasms and easily induced spasms, occurring less than once per hour.
- 3 is spasms occurring between 1 and 10 times per hour.
- 4 is more than 10 spasms per hour.
Evaluation
Clinicians may be presented with a patient who has (1) new-onset spasticity as an initial symptom of an underlying neurological illness or (2) as existing spasticity that has worsened as a result of the progression of the known chronic neurologic condition or an aggravating factor. When evaluating a patient with new spasticity, the clinician must obtain a history and progression of the symptoms, including any motor weakness, altered sensation, pain, bladder and/or bowel dysfunction, and sexual dysfunction. Additionally, a complete history should include family history, travel history, diet, and any compromised immunity. The physical exam should include a neurological evaluation of muscle tone, motor power, reflexes, and sensation.
For a patient with worsening of chronic spasticity, which is often a more common reason for consultation than new onset spasticity, a clinician must evaluate for any triggers, disease progression, and the possibility of a new disease. Triggers may include skin, visceral, drug-related, or device-related issues. Skin issues may present as ulcers, ingrown toenails, boils, and infections. Visceral issues include constipation, urinary tract infections, or calculi. Rapid withdrawal of antispasmodic agents can lead to worsening spasticity. Lastly, poor seating, an ill-fitting orthotic, or failure of an intrathecal baclofen pump can all be device-related triggers. Spasticity also can be worsened by other noxious stimuli such as infections, injuries, deep vein thromboses (DVT), or stress.[3][2][3]
Treatment / Management
When considering treatment for spasticity, the clinician must take into account the etiology of the spasticity, the timing of onset, medical comorbidities, the patient’s support system, and the overall goals of management. As with other conditions, treatment options follow a stepwise approach, starting with more conservative routes and extending to more invasive surgical procedures. One of the initial treatment approaches involves identifying and avoiding noxious stimuli, such as infection, pain, DVT, heterotopic ossification, pressure ulcers, urinary retention or stones, and ingrown toenails. Next, it is crucial to implement physical modalities and therapeutics, such as stretching, splinting, serial casting, heat and cold modalities, direct tendon pressure, functional electrical stimulation, vibration, and biofeedback.[10] Pharmacotherapy offers several options currently approved by the Food and Drug Administration (FDA). These include baclofen, tizanidine, dantrolene, and diazepam. These systemic medications may provide relief in cases of mild to moderate spasticity, and have their best effects in spasticity secondary to SCI or MS. Though these agents may reduce tone and decrease pain, they have not been shown to improve function significantly.[4]
Baclofen: This functions as gamma-aminobutyric acid (GABA) agonist at GABA receptors, thereby increasing the overall inhibitory effects within the reflex pathway.[11] By activating presynaptic GABA receptors, the influx of calcium is reduced, suppressing the release of excitatory neurotransmitters from the presynaptic axon. Activation of postsynaptic GABA receptors increases potassium egress and maintains membrane polarization, making it more difficult to depolarize the postsynaptic cell and decreasing the effect of any excitatory neurotransmitters released from the presynaptic axon. As a result, this decrease in neuron excitability also decreases input to muscle fibers as well as muscle spindle sensitivity.[12] Side effects of baclofen include sedation and drowsiness, to which the patient may develop tolerance with time. Baclofen may also lower the seizure threshold and cause muscle weakness, gastrointestinal symptoms, tremors, insomnia, and confusion.[13] Baclofen is the drug of choice for spinal forms of spasticity and MS and also is used for TBI-induced spasticity. Sudden withdrawal of baclofen can lead to seizures, hallucinations, rebound spasticity with associated fever, renal failure, and death. Thus, the discontinuation of baclofen requires a slow taper. Baclofen has renal metabolism, so in patients with the underlying renal disease, the dosage must be adjusted accordingly. If changing to intrathecal baclofen from oral, there may be an association with withdrawal, as the cerebral concentration is relatively low compared to oral use. Baclofen also poses a theoretical interference with recovery after TBI. Dosing typically starts at 5 mg two or three times a day, and maybe increased by 5 mg every 3 to 5 days, up to 80 mg/day, the FDA-recommended maximum dose. However, higher doses have been reported to be tolerated just as well.[14]
Tizanidine: This drug is an alpha-2 adrenergic agonist, chemically related to clonidine. Its mechanism of action is to enhance presynaptic inhibition of the spinal reflex. Its side effects include sedation and drowsiness in up to 50% of patients, liver damage, hypotension, dry mouth, bradycardia, and dizziness. Clinical trials have shown tizanidine to be as effective as oral baclofen or diazepam but with better overall tolerability.[15] Precautions to take with tizanidine include frequent monitoring of liver function tests (LFTs), as it is metabolized by the liver. Additionally, tizanidine requires frequent dosing due to its short half-life and is contraindicated if simultaneously using intravenous ciprofloxacin due to cytochrome P450 inhibition. Dosing for tizanidine begins at 2 to 4 mg/day, typically at bedtime, and may gradually be increased in dose and frequency to 36 mg/day divided 3 to 4 times a day, depending on patient tolerance.[16]
Dantrolene Sodium: This is unique to spasticity treatment when compared to other agents because it acts peripherally at the level of the muscle by blocking the release of calcium from the sarcoplasmic reticulum.[17] As a result, a reduction of extrafusal muscle fiber contraction strength and muscle spindle sensitivity is achieved. Dantrolene minimally affects smooth or cardiac muscle. An important adverse effect is that 1% of patients suffer from liver toxicity. The highest risk is in female patients over the age of 30 who have been taking higher doses for more than 2 months. This liver toxicity carries with it the risk of hepatonecrosis, so LFTs should be monitored closely. Additional adverse effects include drowsiness, sedation, weakness, fatigue, paresthesias, diarrhea, nausea, and vomiting. Dantrolene is the preferred agent for spasticities of cerebral origin, such as CP or head injury. Its use is often limited in SCI and MS due to its associated adverse effect of weakness.[11] It is also used as a treatment for malignant hyperthermia, neuroleptic malignant syndrome, and hyperthermia from baclofen withdrawal. Dosing begins at 25 mg twice daily to be increased to 400 mg daily, divided into doses two or three times a day.
Diazepam: This functions by facilitating GABA’s effects on GABA receptors, leading overall to membrane hyperpolarization and decreased firing of neurons. Its net effect is increased presynaptic inhibition and reduced reflexes.[13] Of all the aforementioned antispasmodic agents discussed, diazepam is the most sedating. It also can lead to memory impairment and decreased REM sleep. However, it has shown to be beneficial for spasticity due to MS and SCI.[12] It is often unsuitable in TBI patients due to its side effect of memory impairment.[18] Diazepam undergoes hepatic metabolism, so its clearance can be affected by concurrent use of other hepatically metabolized agents, and it can have a very long half-due to its active metabolites. If used together with alcohol, it can lead to a significant central nervous system (CNS) depression. Diazepam overdose can be treated with flumazenil, and like other agents, may lead to withdrawal symptoms if not tapered gradually.[19] The starting dose is typically 4 mg at bedtime or 2 mg twice a day and can be increased to 60mg per day.
In addition to oral agents, spasticity can be managed with local interventions, such as diagnostic nerve blocks, chemical neurolysis, chemodenervation with botulinum toxin, and motor point blocks. These procedures are the typical choice for treatment of focal spasticity or when the systemic effects of the oral agents mentioned above are prohibitive at required treatment doses.[4]
Diagnostic Nerve Blocks: A local anesthetic is injected perineurally using electrostimulation as guidance to block nerve conduction for a few hours. This temporary measure allows the clinician to plan for more permanent interventions such as chemoneurolysis, botulinum toxin, or possible surgery because seeing the temporary reduction in spasticity allows for assessment of potential benefits to be obtained from longer-lasting procedures. These local anesthetics function by blocking the voltage-gated sodium channels on the axon, thereby preventing the depolarization of the axon membrane and interrupting the travel of the signal along the axon. Local anesthetics should not be injected through infected skin or skin that cannot be properly cleaned. Common agents used include lidocaine and bupivacaine.
Chemoneurolysis: Chemical neurolytic agents function for anywhere between months and years. These agents cause demyelination and axonal destruction via protein denaturation and axonal necrosis.[20] These agents also are injected using electrostimulation or electromyography (EMG) guidance. Agents used for these procedures include phenol and ethyl alcohol.[12][21] Phenol typically is used in concentrations ranging from 2% to 7%. Lower concentrations achieve demyelination, leading to a transient anesthetic effect, but achieve minimal axonolysis. The effects of higher concentrations are neurolytic as they destroy axons, lasting greater than 6 months. Ethyl alcohol should be used at a concentration of 45% to 100% to achieve neurolytic effects. It is less commonly used than phenol and is less toxic. A common adverse effect of chemoneurolysis is dysesthesias, which means pain in the sensory distribution of the blocked nerve. The reported incidence ranges from 10% to 30%, lasting weeks to months. Additional adverse effects are muscle weakness (which may be permanent), transient swelling or nodule formation within the muscle itself, DVT, sprains, and skin sloughing (more common when injecting phenol). Phenol, if injected intravascularly, can lead to serious systemic reactions such as convulsions, CNS depression, and cardiovascular failure. Therefore, the usual dose of phenol is well below its lethal dose (8.5 grams), limited to 20 to 30 mL of 5% concentration. Ethyl alcohol has minimal systemic side effects if injected intravascularly.[22]
Chemodenervation with Botulinum Toxin: This is another treatment option. The FDA has approved three type A toxins, onabotulinumtoxin A, incobotulinumtoxin A, and abobotulinumtoxin A, and one type B toxin, rimabotuinumtoxin B, for clinical use.[21] Currently, onabotulinumtoxin A is approved for use in both upper and lower limb spasticity in five specific muscles, and incobotulinumtoxin A has been approved for upper limb spasticity. All serotypes function at the neuromuscular junction, where they block the presynaptic release of acetylcholine. The toxin is taken up by the nerve terminal, affecting the SNARE complex and its components: synaptobrevin, SNAP-25, and syntaxin. The botulinum toxin is released from the bacterium Clostridium botulinum in the form of one heavy and one light chain. The light chain is the active portion, and once it enters the host cell cytoplasm, it cleaves to the host protein SNAP-25, which is responsible for fusion. Once cleaved, SNAP-25 is not able to fuse vesicles. Thus, the overall effect is to prevent the exocytosis of acetylcholine-containing vesicles into the nerve terminal cleft, causing chemical denervation. Botulinum toxin is contraindicated in patients with a known sensitivity if there is evidence of infection at the planned injection site. The toxin should be used with caution if a patient is undergoing concurrent treatment with aminoglycoside or spectinomycin antibiotics. Patients with an underlying neuromuscular disease, such as amyotrophic lateral sclerosis (ALS), myasthenia gravis, Lambert-Eaton syndrome, or peripheral motor neuropathic disease, are at increased risk of severe reactions including respiratory depression or dysphagia. As above, electrical stimulation, EMG, or ultrasound are all methods to localize the muscle in question.[23] The clinician also should be aware of the dose-dependent response, meaning that more toxin load per muscle results in increased weakness clinically. Onabotulinumtoxin A is typically injected in units ranging from 25 to 200 per muscle, depending on muscle size, function, patient weight, and amount of spasticity. The typical effect of the toxin lasts up to 3 months, at which point the patient may need re-injection. The toxin takes 24 to 72 hours to take action and achieves peak effect between 4 and 6 weeks, from which clinicians refer to the “rule of 3s”: 3 days for initial effect, 3 weeks for peak effect, 3 months duration. Adverse effects are typically benign and include unwanted weakness in adjacent muscles, hematoma, local bruising or swelling, flu-like symptoms, dysphagia from the cervical injection (transient), and injection site pain.[24][25]
Intrathecal Baclofen Pump: Another management option is an intrathecal baclofen (ITB) pump. This device allows for direct delivery of baclofen into the cerebrospinal fluid (CSF) in the intrathecal space. This allows a patient to receive a high concentration of the medication directly to the spine while decreasing the CNS risks associated with high oral doses of baclofen, with a ratio of 100:1 for the baclofen concentration at the spinal cord level when administered intrathecally versus orally.[26] The components include a pump and reservoir implanted subcutaneously within the abdominal wall and a catheter placed into the intrathecal space. A programmable battery-powered pump stores and delivers the baclofen via an electronic schedule. The pump is refilled on an intermittent basis via transcutaneous injection. The frequency of refill depends on the infusion rate and the size of the pump reservoir. The dose can be adjusted via the electronic programmer at any time. The pump also has a programmable alarm system to alert the patient, caregiver, and clinician when the reservoir is running out of medication or when there has been a pump malfunction.[14]
Symptoms of baclofen overdose include hypotonia or severe weakness, somnolence, nausea/vomiting, hypotension, respiratory depression, and seizures. Symptoms of baclofen withdrawal include fever, nausea, hyperthermia, dizziness, insomnia, pruritis, hallucinations, altered mental status, and exaggerated rebound spasticity.
ITB pump is indicated for patients with generalized spasticity who either cannot tolerate or lack response to more conservative agents (oral, nerve blocks, etc.).[27] Once again, the clinician must be careful to evaluate the utility of a patient’s spasticity to their daily function. Before implanting an ITB pump, the patient must undergo trials through a single intrathecal bolus or continuous infusion through a percutaneous catheter. Multiple trials of increasing doses may be performed to establish clinical benefit. If the patient demonstrates a significant decrease in tone or spasms, he or she may be a good candidate for pump placement. The initial pump infusion dosing is typically calculated by doubling the initially clinically effective dose and using this for the initial 24-hour infusion dose. An ITB pump requires strict compliance, as it needs regular monitoring and refilling, and withdrawal can be lethal.[12]
Surgery: The most invasive management options are surgical. These include orthopedic surgeries such as tendon lengthening, tendon transfer procedures (such as the split anterior tibial tendon transfer known as SPLATT) as well as neurosurgical procedures such as sectioning at the level of a peripheral nerve (neurectomy), central electrical stimulators, rhizotomy, and neuroablative procedures.[28]
Differential Diagnosis
The differential diagnoses for spasticity include contractures, rigidity, and catatonia. A contracture is defined as a decreased elasticity of a muscle, tendon, ligament, joint capsule, and skin, leading to increased resistance during the passive stretch, similar to spasticity. However, the difference between the two is that contractures do now show any velocity-dependent changes with movement or limb positioning. Rigidity is most commonly associated with basal ganglia injuries. Rigidity, unlike spasticity, exhibits high tone that is non-selective and affects all muscles surrounding a particular joint equally. Similar to a contracture, rigidity is unaffected by the speed of movement and is constant throughout the range of movement. Catatonia is a neuropsychiatric disorder in which the patient exhibits abnormal posturing; the increase in muscle tone seen here is dependent on the force applied to the muscle in question. Unlike spasticity, catatonia frequently presents with concomitant signs such as stupor, impulsivity, perseveration, staring, grimacing, echolalia, echopraxia, and withdrawal.[3]
Spasticity