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Neurosurgical Treatment of Spasticity

by Joseph R. Madsen, MD

Spasticity is the condition of abnormal movements resulting from overly active reflexes and abnormal control of limb movements due to malfunctioning circuits in the spinal cord. Reflexes have been well studied since the time of Sherrington, as one of the most primitive responses of the nervous system. It is known that when input to spinal cord neurons from higher centers is lacking, as in brain injury or spinal cord injury, these circuits become hyperactive so that reflex movements can be exaggerated. In children, frequently treated causes of spasticity include cerebral palsy, which includes a wide variety of motor dysfunctions related to brain problems acquired near the time of birth, as well as severe head injuries, encephalitis, near drowning, congenital malformations of the nervous system, and spinal cord injury. The management of spasticity requires close cooperation among several medical disciplines, including primary care physicians, neurologists, orthopedists, physiatrists, physical therapists, and, in some cases, neurosurgeons. This discussion will focus on the neurosurgeonÕs role in treating spasticity, but it is not intended to minimize the important and more frequent roles of the other specialties.

Two major neurosurgical approaches are available for directly attacking the underlying abnormal circuitry in spasticity: rhizotomy (literally root cutting and placement of baclofen pumps.

Rhizotomy involves interrupting some of the nerve roots which mediate the overly active reflex circuit. The most common procedure is selective dorsal rhizotomy (SDR). The rationale for this procedure is that partial elimination of the tiny sensory fibers entering the spinal cord can decrease the intensity of feedback, so as to diminish the hyperactive, spastic motor response. Although this procedure was first proposed and performed by Foerster in the early part of this century, it fell out of practice because of a high complication rate, only to be rediscovered and popularized in the 1970s. Part of the reason for its resurgence has been the addition of electrophysiological studies to permit better identification of roots and to study the abnormal reflexes at the time of surgery. Considerable controversy has surrounded the need and advisability of complex electrophysiological testing in these cases.

Research at Children's Hospital has concentrated on the detailed study of responses to single spike electrical stimulation of a sensory nerve root, as measured by the motor responses in the muscles (EMG). We have found that many of the motor responses to dorsal nerve root stimulation are in fact not reflexes at all. Since they are not reflexes, they cannot be used in the decisions about which nerve roots ought to be cut. These responses are useful, however, in determining the identity of each nerve root in terms of where it projects in the motor system. Thus, a simple protocol for measuring the presence of nerve root responses has allowed us to be not only selective about the fibers to cut to interrupt the spastic reflexes, but also selective in the sense of which data can be rationally interpreted and which cannot. The references cited below provide technical information on our experience with this.

Intrathecal baclofen. A separate strategy for the management of spasticity by neurosurgeons involves the use of surgery to supply a substitute neurotransmitter to the spinal cord to permit muscle relaxation. Baclofen is a drug which was designed to match the structure of GABA (gamma amino butyric acid), the major inhibitory neurotransmitter in the central nervous system. Because of spasticity is in part a lack of inhibition from the higher levels in the nervous system, direct replenishment of this inhibitory pathway makes sense as an approach to treat spasticity. A pump has been designed especially for this purpose, which can be implanted under the skin with a small catheter going into the spinal canal to deliver the drug. The pump is accessed from outside the skin and can be programmed by an external computer to give a very precise dose of the medication. This system has been extensively used in spinal cord injury, and has recently been approved by the FDA for treatment of spasticity and head injury and cerebral palsy. Published reports also describe the utility of this intrathecal Baclofen therapy in dystonic and other complicated spastic states.

In the evaluation of spastic patients for neurosurgical treatment at Children's Hospital, we typically select those with a particular need for tunability for intrathecal Baclofen treatment. This would include patients who rely on the spasticity to allow upright posture, or may have borderline underlying trunk strength so that complete removal of the spasticity by rhizotomy may be inadvisable.

Patient Evaluation. For either rhizotomy or Baclofen pump insertion, a multidisciplinary evaluation, including neurological, orthopedic, and physical therapy evaluation is crucial. Sometimes, specific pre-operative tests of so-called H reflex, or electrophysiological analog of the reflex strength, is useful. Arrangements for this multidisciplinary evaluation and consultation regarding the need or validity of any of these procedures can be arranged by contacting the office of Dr. Joseph Madsen at (617) 355-6005.

Selected references:

Logigian EL, Wolinsky JS, Soriano SG, Madsen JR, Scott RM. H reflex studies in cerebral palsy patients undergoing partial dorsal rhizotomy. Muscle & Nerve 1994; 17:539-549.

Soriano SG, Logigian EL, Prahl PA, Scott RM, Madsen JR. Nitrous oxide depresses the H-reflex in children with cerebral palsy. Anesthesia & Analgesia 1995; 80:239-241.

Logigian EL, Shefner J, Soriano SG, Goumnerova L, Scott RM, Madsen JR. The critical importance of stimulus intensity in intraoperative monitoring for selective dorsal rhizotomy (DR). Muscle & Nerve, 1996; 19:415-422.

Madsen JR, Scott RM, Logigian EL. The latency test: criterion for valid reflexes in dorsal rhizotomy surgery. American Society of Pediatric Neurosurgeons abstract, 1995.

Madsen JR. After neurotrauma: Brain and spinal cord repair. Harvard Mahoney Neuroscience Institute Letter 1996; 5: 1, 1-7.

Gilmartin R, Bruce D, Storrs BB, Abbott R, Krach L, Ward J, Bloom K, Brooks WH, Johnson DL, Madsen JR, McLaughlin JF, Nadel J. Results of a multicenter trial of intrathecal lioresal (baclofen injection) for the management of spastic cerebral palsy. Submitted to Pediatric Neurosurgery, 1997.

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