Residency · Residency · Neurosurgery

Spasticity Management: Intrathecal Baclofen and Selective Dorsal Rhizotomy

Introduction

Spasticity is a velocity-dependent increase in muscle tone resulting from hyperexcitability of the stretch reflex, caused by upper motor neuron lesions. It is a common sequela of cerebral palsy, traumatic brain injury, spinal cord injury, stroke, and multiple sclerosis. Neurosurgical interventions including intrathecal baclofen pump therapy and selective dorsal rhizotomy play a central role in managing severe, refractory spasticity.

Pathophysiology of Spasticity

Spasticity develops from loss of descending inhibitory input through the corticospinal and reticulospinal tracts to spinal motor neurons. This creates an imbalance between excitatory and inhibitory interneuron circuits in the spinal cord, resulting in enhanced Ia afferent monosynaptic reflex arc activity. Over time, secondary changes develop including muscle fiber shortening, fibrosis, and fixed contracture. The distinction between spasticity, which is velocity-dependent, and dystonia, which involves sustained involuntary co-contraction, is essential for treatment planning because the two respond differently to surgical interventions.

Clinical Assessment

The Modified Ashworth Scale grades muscle tone from 0 (normal) to 4 (rigid). The Tardieu Scale assesses the velocity-dependent catch and is more specific for true spasticity. The Gross Motor Function Classification System categorizes cerebral palsy patients into levels I through V. Goal-directed assessment determines whether spasticity is functional, aiding activities such as standing and transfers, or detrimental to the patient. Triggers for spasticity exacerbation must be evaluated, including urinary tract infection, skin breakdown, constipation, and pain.

Medical and Non-Surgical Management

Physical therapy and stretching form the cornerstone of all spasticity management. Oral medications include baclofen, tizanidine, dantrolene, and diazepam, though their use is limited by sedation and cognitive effects. Botulinum toxin injections provide focal spasticity management with a temporary effect lasting 3 to 4 months. Phenol and alcohol nerve blocks offer longer duration but carry risk of dysesthesia. Serial casting and orthotics help prevent contracture development.

Intrathecal Baclofen Therapy

Mechanism and Indications

Baclofen is a GABA-B receptor agonist that reduces spinal reflex activity. Intrathecal delivery achieves CSF concentrations 100 times higher than oral dosing while using only 1 percent of the systemic dose, dramatically reducing side effects. Indications include severe generalized spasticity refractory to oral medications, whether of spinal or cerebral origin. ITB is appropriate for patients at GMFCS levels IV to V, or level III with significant functional limitation.

ITB Trial

A screening trial is performed before pump implantation. A lumbar puncture delivers 50 to 100 micrograms of intrathecal baclofen as a bolus, and the response is assessed at 1, 2, 4, and 6 hours using the Ashworth scale. A positive response is defined as a reduction in Ashworth score by at least 1 point. If no response occurs at 50 micrograms, the trial may be repeated at 75 and then 100 micrograms on separate days.

Pump Implantation

A programmable pump such as the Medtronic SynchroMed II is placed in a subcutaneous abdominal pocket. A catheter is tunneled subcutaneously and inserted into the lumbar thecal sac with the tip typically positioned at the T10 to L1 level. The pump reservoir holds 20 to 40 milliliters and is refilled percutaneously every 1 to 6 months. The starting dose is approximately double the effective trial dose divided over 24 hours, with titration over weeks to months for optimal effect.

Complications

Catheter-related problems are the most common complications, occurring in 10 to 30 percent of cases, and include kinking, migration, disconnection, and fracture. Infection of the wound or meningitis affects 5 to 10 percent. ITB withdrawal syndrome is potentially life-threatening, presenting with rebound spasticity, hyperthermia, rhabdomyolysis, and multi-organ failure. ITB overdose causes respiratory depression, drowsiness, and coma. Pump malfunction and battery depletion require surgical replacement every 5 to 7 years.

Selective Dorsal Rhizotomy

Mechanism and Indications

SDR involves selective sectioning of dorsal sensory nerve rootlets from L1 through S1 or S2 that contribute to the abnormal reflex arc. By reducing the afferent limb of the stretch reflex, spasticity is decreased while motor function is preserved. The ideal candidate is a child with spastic diplegic cerebral palsy at GMFCS levels II to III, aged 3 to 8 years, with good underlying voluntary motor strength, no fixed contractures, and adequate cognition to participate in intensive rehabilitation.

Surgical Technique

The procedure is performed through either a single-level laminectomy at L1 or a multi-level laminoplasty approach. Dorsal rootlets from L2 to S1 or S2 are identified using anatomical and electrophysiological criteria. Intraoperative EMG monitoring involves stimulation of individual rootlets at threshold and supramaximal levels. Rootlets demonstrating abnormal sustained or spreading EMG responses are sectioned, with typically 50 to 70 percent of dorsal rootlets divided at each level. Preservation of S2 rootlets is critical for maintaining bladder and bowel function.

Outcomes

SDR produces sustained long-term reduction in spasticity. Functional improvement is documented by gains in GMFM-66 scores and improved gait quality. Intensive postoperative physiotherapy for a minimum of 6 to 12 months is essential for optimal outcomes. Long-term studies demonstrate durable benefits at over 20 years of follow-up.

Complications

Sensory changes including dysesthesia and numbness in the lower extremities occur but are transient in most patients. Bladder dysfunction is usually transient and minimized by careful rootlet selection. Spinal deformity including scoliosis and lordosis is more common with multi-level laminectomy approaches. Weakness can result if excessive rootlets are sectioned or motor rootlets are inadvertently divided.

ITB vs. SDR: Decision-Making

The choice between ITB and SDR depends on several factors. ITB is appropriate for generalized spasticity affecting all four limbs, GMFCS levels IV to V, and cases where the dystonia component is significant. It is reversible and adjustable, suitable for any age, and requires ongoing maintenance with refills and battery changes. SDR is appropriate for predominantly lower extremity spasticity, GMFCS levels II to III, and is a one-time irreversible procedure. It is best performed between ages 3 and 8 and is not effective for dystonia.

Clinical Pearls

Always distinguish spasticity from dystonia before surgical planning; ITB can address both conditions, while SDR is effective only for spasticity. ITB withdrawal is a medical emergency that mimics malignant hyperthermia or neuroleptic malignant syndrome; oral baclofen and benzodiazepines should be administered immediately while the pump system is evaluated for catheter malfunction. SDR outcomes are highly dependent on patient selection; children with predominantly spastic diplegia and good volitional motor control benefit most. All patients undergoing spasticity surgery require a long-term, multidisciplinary rehabilitation plan for optimal outcomes.

References

1. Albright AL, Gilmartin R, Swift D, et al. Long-term intrathecal baclofen therapy for severe spasticity of cerebral origin. J Neurosurg. 2003;98(2):291-295.
2. Park TS, Edwards C, Liu JL, et al. Beneficial effects of childhood selective dorsal rhizotomy in adulthood. Cureus. 2017;9(3):e1077.
3. Hasnat MJ, Rice JE. Intrathecal baclofen for treating spasticity in children with cerebral palsy. Cochrane Database Syst Rev. 2015;(11):CD004552.
4. McLaughlin J, Bjornson K, Temkin N, et al. Selective dorsal rhizotomy: efficacy and safety in an investigator-masked randomized clinical trial. Dev Med Child Neurol. 2002;44(1):17-25.

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