Patient Selection

Candidates for ITB usually have spastic quadriparesis with mean Ashworth scores of 3 or greater in the upper and lower extremities (Table 226-1). Most have had no significant improvement with oral medications and botulinum toxin injections, but ITB is occasionally appropriate for children with severe spastic quadriparesis who have had no previous treatments because the likelihood of sufficiently improving severe spasticity with oral medications is low. Their spasticity is either impeding caregiving, causing progressive contractures, interfering with function, or causing pain. ITB is used most often in children who weigh 15 kg or more and are 4 years or older, but with the smaller pumps that are now available, there are virtually no age or size limitations. Palisano and coworkers developed the Gross Motor Function Classification System (GMFCS) to broadly categorize levels of disability of children with CP.⁷ Most children who are candidates for ITB are GMFCS level IV or V, occasionally level III, and rarely level II.

TABLE 226-1 Ashworth and Modified Ashworth Scales

It is important that the patient and caregiver goals with ITB therapy be reasonable and clearly identified preoperatively. “Reducing spasticity” per se is not a therapeutic goal. Appropriate goals include increasing range of motion, facilitating care, slowing the development of musculoskeletal contractures, and decreasing painful muscle spasms.

ITB is rarely administered with the intent of improving gait in patients with CP who have spastic diplegia and should not be considered as an alternative to lumbar rhizotomies; the two modalities are indicated for different groups of patients—young ambulatory patients with spastic diplegia are best treated with lumbar rhizotomies, whereas nonambulatory or minimally ambulatory patients with spastic quadriparesis are better treated with ITB. Administration of ITB can be considered in an attempt to improve gait in young adults with spastic diplegia, but in such cases, infusion screening trials are helpful to evaluate the effects of ITB on gait before a pump is implanted.

Screening

When ITB was first used to treat spasticity of cerebral origin, screening trials were conducted to evaluate its effectiveness before pumps were inserted. Screening trials involved the injection of a bolus baclofen dose, 25 to 100 µg via lumbar puncture, and comparison of spasticity scores in the lower extremities before the injection with scores at 2-hour intervals afterward for 8 hours. Decreases of 1 point in the mean lower extremity Ashworth score were considered to be clinically significant and occurred almost invariably. Since then, hundreds of children with spastic CP have undergone screening bolus injections, which virtually always decrease spasticity, and many centers now forego a screening injection. The advantages of a screening trial include (1) the demonstration that baclofen is effective for that patient and (2) the demonstration that function is at times improved by ITB. Disadvantages of screening trials include (1) the cost and discomfort of the trial (headache, nausea, and vomiting are common), (2) the fact that a bolus dose often causes such hypotonia in the lower extremities that pivot transfers and gait are temporarily worsened, and (3) the common development of headache and vomiting from a CSF leak afterward.

If a screening trial is done, however, measurement of opening pressure may be helpful because the pressure is often abnormally increased, and in such cases the risk for CSF leakage is enhanced when the baclofen pump catheter is inserted.⁸ Alternatively, it is reasonable to perform a quick brain magnetic resonance imaging or computed tomographic scan of the head to see whether ventriculomegaly is present; if it is, insertion of an intracranial pressure monitor for 24 hours will provide a better evaluation of intracranial pressure than a single pressure measurement via spinal tap. If pressures are abnormally high, the likelihood of a CSF leak with the baclofen catheter can be diminished either by inserting a ventriculoperitoneal shunt before pump implantation or by inserting the intrathecal catheter with open techniques (laminotomy and purse-string suture around the entry site).

If improving gait is a therapeutic goal, the effects of ITB on gait can be evaluated before pump placement with an intrathecal catheter connected to an external microinfusion pump. Bleyenheuft and coworkers evaluated gait with continuous infusions of baclofen, 45 to 150 µg/day, in nine patients whose gait was deteriorating.⁹ Gait improved in seven of nine as evaluated on the Observation Gait Scale, and the improvement was present after pump implantation.

Pump and Catheter Implantation

Operations to implant a baclofen pump in patients with CP are done under general anesthesia and usually last 1 to 1.5 hours.¹⁰ Programmable pumps are needed when treating patients with spasticity of cerebral origin because of the frequent need to adjust the ITB dosage. At present, the only commercially available programmable pump is the Medtronic SynchroMed pump, a battery-powered pump with a 7-year battery life. The pump is usually implanted in the abdominal wall, subfascially in most children and thin patients and on the fascia in patients with more subcutaneous fat. In patients with no abdominal site for pump implantation (e.g., because of multiple scars, ostomy sites), the infraclavicular region is an alternative site. The baclofen catheter is connected to the pump and tunneled posteriorly to the lumbar region, where it is inserted via a Tuohy needle into the thecal sac and advanced cephalad to a site that depends on the distribution of the patient’s spasticity: T10-11 for patients with spastic diplegia and C7-T4 for those with spastic quadriparesis. For patients with spine fusions or anticipated spine fusions, catheters can be tunneled obliquely cephalad and inserted into the thecal sac via a small laminectomy at C6-7 above the spine fusion, which usually extends from T1-2 to the sacrum (Fig. 226-1).

FIGURE 226-1 Baclofen pump and the catheter tunneled to enter the thecal sac above the spine fusion.

The initial reports of ITB for the treatment of spinal spasticity associated with spinal cord injury or multiple sclerosis positioned the catheter tip in the T10-12 region. However, Kroin and associates subsequently demonstrated that the concentration of radioisotope administered in the lumbar region was 4 times higher than the concentration at the craniovertebral junction.¹¹ To increase the baclofen concentrations in the cervical region and obtain better reductions in upper extremity spasticity, catheter tips are now positioned higher when treating spastic quadriparesis. Grabb and coauthors reported that higher catheter positions were associated with a better reduction in upper extremity spasticity than was observed with lower catheters.¹² Cervical catheter tip positions do not result in increased complications or adverse side effects and are associated with significantly decreased spasticity in both the upper and lower extremities.

Dosing of Intrathecal Baclofen

After implantation of the pump, ITB doses are titrated over the first few months, regardless of the movement disorder being treated. When treating spasticity, infusions often begin at 100 µg/day and are increased by 10% to 20% daily until spasticity is perceptibly reduced to the patient and physician; doses are then adjusted at less frequent intervals on an outpatient basis. Stable doses are achieved by 6 to 12 months. The average ITB dose at 1 year when treating cerebral spasticity is approximately 300 µg/day. Doses greater than 600 µg/day are uncommonly needed to treat spasticity. Some patients seem to respond better to intermittent baclofen boluses, such as 75 µg every 4 hours, than to continuous infusion, but no studies have been reported in which the effects of continuous infusions were compared with those of intermittent bolus infusions in the same patient.

Tolerance to ITB probably does not develop in people with spastic CP. If patients have been at a stable, effective dose for 2 years but then become more spastic and higher and higher doses do not yield the effectiveness of the initial infusion, there is almost always a malfunction of the infusion system and the problem is generally related to the catheter. Approximately 8% of people with dystonic CP do not achieve satisfactory improvement even at high ITB doses, such as 1500 µg/day. The lack of effect is more likely due to unresponsiveness to ITB than to tolerance.

Outcomes of Intrathecal Baclofen in Patients with Spastic Cerebral Palsy

The efficacy of ITB in reducing spasticity in children and young adults with CP has been documented in multiple publications from both single institutions and multicenter trials.^13,14 Butler and Campbell reviewed the 12 publications on ITB that had been published by 2000 and concluded that spasticity is improved and function is probably improved.¹⁵ Spasticity is significantly decreased in the lower and upper extremities and remains decreased during the years of infusion, probably indefinitely; a multicenter study in 2003 reported sustained decreases in Ashworth scores in the lower and upper extremities during 6 years of follow-up.¹⁴