What is Spasticity?
Spasticity is an abnormal muscular hyperactivity with increase in muscle tone (rigidity), and sustained muscle contractions (spasm), caused by damage to the central nervous system. Spasticity occurs when the damaged brain is unable to generate adequate inhibitory stimulus to the spinal cord or when the damaged spinal cord cannot relay the signals to the alpha motor neuron of the spinal cord. The imbalance results in exaggeration of the excitatory impulses reaching the spinal cord from areas of the body below the neural damage.
Muscle tone is necessary to maintain normal posture. A patient may use a small increase in muscle tone to stand, and transfer from bed to chair. As spasticity worsens, the muscle tightness increases as the patient tries to move, the limbs and body jerk involuntarily, causing pain, and interfering with mobility, sleep, and care.
What causes Spasticity?
The common causes of spasticity are:
1. Spinal cord injury
2. Multiple sclerosis
3. Cerebral palsy
4. Stroke
5. Head injury
What is the standard treatment for Spasticity?
Mild spasticity is treated with physical therapy and stretching exercises. Moderate spasticity often require oral muscle relaxants for effective control. Baclofen is one of the most widely used antispasmodic agents. Higher doses are often required with long-term use. Diazepam is also commonly used, but produces sedation and tiredness. Dantrolene sodium acts directly on muscles and reduces spasticity by inhibiting the inflow of calcium ions. It produces muscle weakness and it can be toxic to the liver. Clonidine and tizanidine act directly on the brain and are associated with drowsiness and hypotension. Injection of botulinum toxin, or nerve blocks may be helpful if the spasticity involves only a few muscles.
Patients who have severe spasticity and do not respond to oral muscle relaxants or those who are unable to tolerate the side effects, may be candidates for intrathecal (spinal) baclofen therapy (ITB). Small doses of baclofen infused into the spinal subarachnoid space through an implantable pump can significantly control spasticity.
Baclofen Pump for treatment of Spasticity
Selection
Not all patients with spasticity should be treated with a pump. Every potential patient will be interviewed and examined by a physician in our department to determine whether or not he or she meets the criteria for treatment with ITB. Questions that will be asked include the onset of symptoms, severity of spasticity, and how it interferes with daily activities or care of the patient. Records or previous and current treatments should be provided. A general neurological examination will be performed, and the degree of spasticity will be graded on two standard scales. The Ashworth Scale is a measure of the degree of muscle tightness or stiffness, while the Spasm Frequency score is determined by the how often the jerky movements occur. Patients must have a mean Ashworth score of at least 3 or Spasm score of at least 2 in the affected limb to be eligible.
Patients with any of the following conditions may not be eligible.
1. History of allergy to baclofen.
2. Severely impaired renal or hepatic function.
3. Seizures that are not well controlled.
4. Presence of systemic infection.
5. Skin that is too thin to hold the pump, or inadequate body size.
6. Pregnancy.
7. Inability to keep follow-up appointments.
Those selected must demonstrate a positive response to a test injection of ITB before they can undergo implantation of the pump.
Screening
The test requires a lumbar puncture, and the baclofen can be injected directly through the needle, or via an intrathecal catheter. The test is stopped as soon as a positive response is noted. Otherwise, a higher dose is administered on the following day. A reduction in the mean Ashworth score or the mean Spasm score by two or more points for at least four hours is considered to be a positive response
Patients who do not have a positive response are not candidates for the pump.
Implantation of Pump
There are two main types of pumps that can be implanted for administration of baclofen to the spinal cord. The first type of pump is called a programmable pump because the dose and timing can be programmed into the pump and changed by the use of an external, battery-powered computer called a programmer. The second type is a fixed rate pump which is powered by the expansion of anti-freeze in a sealed chamber. Most pumps are about the size of a hockey puck. Our experience is that most patients require frequent dose adjustments during the first few months after implantation of the pump. Therefore, our preference is to use a programmable pump during the initial placement.
The implantation is done in the operating room with the patient on the side so that there is access to the lower back and the anterior abdomen. We have done some of the surgery under local anesthesia, now almost always use general anesthesia because we have found it to be safe, and to provide the most comfort for the patient. A small incision is made in the lower back (lumbar area) and needle is inserted into the spine in the space occupied by cerebrospinal fluid (intrathecal space). Rarely, the presence of severe arthritis or deformity of the spine may make it necessary for the surgeon to remove a small portion of the back of the spine (laminectomy) before the needle can be successfully passed into the intrathecal space. A small tube (catheter) is introduced into the space through the needle. A second incision, about 3 to 4 inches long is made across the front of the abdomen on one side. A special rod is passed under the skin from the abdomen to the back, and the catheter is tunneled to the abdomen. The pump is filled with baclofen solution and the appropriate dose is programmed in. It is then connected to the pump and placed under the skin of the abdomen.
We like the patient to stay in bed with the head flat for at least 12 hours to reduce the chances of getting a headache from the lumbar puncture. Patients who were taking oral baclofen just prior to surgery will be weaned off the oral medication over a few weeks. Abrupt cessation can lead to confusion, anxiety, hallucination and symptoms of withdrawal.