Learning Objectives: After participating in this CME activity, the neurosurgeon should be better able to:
- Assess spasticity and the mechanism of action for intrathecal baclofen therapy.
- Evaluate the appropriate indications for institution of intrathecal baclofen therapy.
- Distinguish the basic steps for surgical placement of a subcutaneous pump and spinal catheter and complications associated with the procedure.
Spasticity and generalized dystonia are significant medical problems that effect various patient populations. Systemic medical treatments include baclofen and other medications such as tizanadine and benzodiazepines. Many of these medications cross the blood-brain barrier poorly, only producing a low concentration of drug in the central nervous system. Due to systemic side effects, and the difficulty achieving blood levels sufficient to satisfactorily treat spasticity and generalized dystonia, it is often necessary to employ subcutaneous pumps and spinal catheters that allow intrathecal dosing of baclofen. Intrathecal baclofen therapy can be very efficacious for properly selected patients, but there are significant risks that the practitioner and the patient must bear in mind; these include infection, wound breakdown, catheter malfunction, and adverse medication events. As with any surgical treatment, patient selection and appropriate surgical technique are crucial if one is to maximize the benefits of therapy and minimize complications. With appropriate patient selection and surgical technique, intrathecal baclofen therapy is a rewarding endeavor that significantly improves patient and caregiver quality of life.
Indications for Surgical Treatment
Patient selection begins with making an appropriate diagnosis. Spasticity and secondary generalized dystonia are the most common diagnoses treated with intrathecal baclofen administration. Spasticity is defined as velocity-dependent resistance to movement; the result is resistance to passive or active movement of the patient's body. Dystonia is defined as muscle spasms that result in unwanted postures and movements.
Any upper motor neuron injury has the potential to produce spasticity. Common causes include cerebral injury or spinal cord injury. Patients with traumatic spinal cord injury, cerebral palsy, hereditary spastic paraparesis, stroke, and traumatic brain injury can suffer from marked spasticity. The Ashworth scale is used to grade spasticity and ranges from 1 to 5, where 1 is normal tone and 5 means the affected area remains in rigid flexion or extension. Ashworth Grade 2 is manifested by a “catch” with motion. Grades 3 and 4 are differentiated by increased tone with ease of passive movement or increased tone with difficult passive movement, respectively. When examining patients with spasticity, it is important to differentiate the fixed limb position due to muscle contractures (fibrosis) from that associated with increased muscle tone.
Secondary dystonia, usually the result of brain injury from infarct or infection, must be differentiated from primary dystonia, which is often linked to a specific genetic mutation (ie, the DYT1 mutation). Primary dystonia is usually best treated with deep brain stimulation of the globus pallidus interna, whereas secondary dystonia is most commonly treated with intrathecal baclofen.
Oral medications generally considered for use before the implementation of intrathecal baclofen therapy include diazepam, dantrolene, tizanidine, and, of course, oral baclofen. If the side effects of these medications are intolerable or their effectiveness is insufficient, surgical management of spasticity should be considered because of the serious consequences of untreated spasticity and dystonia. In addition to causing pain and discomfort these conditions can significantly complicate patient positioning, hygiene, and care. Bladder spasticity can result in frequent urination leading to skin breakdown. In some cases spasticity can result in decubitus ulcers, which may result from difficulty in maintaining an appropriate seated posture secondary to spasticity or dystonia. If a patient continues to suffer from spasticity or dystonia despite maximal medical therapy, then surgical therapy must be considered.
Surgical therapies for spasticity fall into the categories of ablative and modulatory. Ablative therapies include neurectomies, rhizotomies, myelotomies, myotomy, and tenotomy. Intrathecal baclofen infusion, by a subcutaneous pump, is considered modulatory because of the adjustable and reversible nature of the therapy. Ablative therapies have the advantage that they do not require the maintenance and expense of an implanted system, but they are not titratable. When selecting a patient for intrathecal baclofen therapy, the practitioner must ensure that the patient has adequate logistic and social support to maintain the system because periodic refills and adjustments are required. Both patient and caregiver education is required for successful implementation of this therapy. A team approach with reliance on physical medicine and rehabilitation physicians or movement disorders specialists can be very helpful to successful implementation of intrathecal baclofen therapy. For many practitioners and patients, intrathecal baclofen therapy has become a preferred modality for treating spasticity and secondary generalized dystonia.
Mechanism of Action
From a mechanistic standpoint, spasticity is the end result of decreased inhibition of α-motor neurons. In the normal reflex arc, the actions of Ia afferents from interfusal muscle spindle cells are dampened by the inhibitory influence of motor neurons above the level of the α-motor neurons in the anterior horn of the spinal gray matter. In the case of upper motor neuron injury such as in spinal cord injury or cerebral palsy, the inhibitory influence that upper motor neurons exert on spinal α-motor neurons is reduced or absent. This results in a pathologic reflex arc that causes an exaggerated and pathologic response to muscle stretch. The result is the commonly seen phenotypes associated with spasticity and secondary dystonia. This includes dystonia and marked velocity-dependent resistance to movement. Baclofen can reduce symptoms by its action on γ-aminobutyric acid type B (GABAB) receptors. Action of this GABAB agonist reduces the excitation that Ia muscle spindle afferents exert on α-motor neurons. Therefore, the lack of upper motor neuron inhibition is not felt as acutely because there is less excitation from Ia muscle spindle afferents. Baclofen may also have some activity in decreasing nociception.
Preoperative and Postoperative Considerations
Several points are important to consider before initiating intrathecal baclofen therapy. These include efficacy of the treatment and ability of the patient to tolerate the procedure and maintain the system.
To predict efficacy of the intrathecal baclofen therapy, some practitioners advocate for a trial intrathecal injection of baclofen. During a trial, a lumbar puncture is performed in the standard fashion and 50 to 75 μg of baclofen is injected into the intrathecal space. The patient's spasticity and tone are both monitored by a physical therapist pre- and postinjection to evaluate for any improvements. For ambulatory patients, this also allows an assessment of their ability to ambulate with decreased tone. It is important to caution that a single bolus of intrathecal baclofen may not be equivalent to continuous infusion of small amounts of the medication via a catheter that usually terminates well above the insertion site for a lumbar puncture. Another strategy is to trial only ambulatory patients, which you are concerned, who may be reliant on their tone for continued ambulation. This allows patients some indication of how essential tone is to their ambulation, and it may prepare them better for the postoperative period and provide more information for their decision-making process. Overall, making the determination of a diagnosis that is favorable for the initiation of baclofen therapy is the best predictor of efficacy. Many patients may not require an injection trial before initiated continuous infusion baclofen therapy.
Anatomic considerations include the patient's body habitus and spinal anatomy. With regard to body habitus, many patients with marked dystonia or spasticity or dystonia have low body mass indices. This raises the possibility that it may be difficult to achieve tissue coverage, and the risk of hardware erosion is increased. Placing a smaller pump may be reasonable, but this tactic only incrementally decreases the difficulty with tissue coverage and necessitates more frequent refills. Preoperative tissue expanders can also be considered as an option for improving tissue coverage in small group of patients.
The spinal catheter generally can be placed with a Tuohy needle at the level of L2-L3. However, many patients undergoing intrathecal drug delivery therapy have had prior spinal surgical procedures or suffer from marked scoliosis. Delineation of the spinal anatomy requires plain x-rays of the spine at a minimum, and we perform a preoperative MRI of the spine in all regions that the catheter will traverse, to rule out any significant spinal stenosis. If fusion mass is present or scoliosis is severe, in a patient where a cervical placement is desired, the surgeon may need to introduce the spinal catheter by an alternative method. In either of these cases, alternative entry points and methods may need to be considered. In cases with an entry point at or above the level of the conus, or if there is substantial fusion mass, a laminotomy is needed to insert the spinal catheter. If one is near the spinal cord, the dura is opened with a scalpel and the spinal catheter is inserted under direct vision to minimize the risk of spinal cord injury. In cases where a laminotomy is performed, it is advisable to place a small purse string suture in the dura around the catheter to minimize leaking.
Postoperative considerations are important to successful initiation of intrathecal baclofen therapy. Many patients with spasticity or secondary dystonia are debilitated and have significant mobility issues. It is important that these patients have an adequate support network and that a patient be allied with practitioners that can refill and program the pump. Some ambulatory patients have decreased ability to ambulate in the immediate postoperative period; therefore, they may require a short stay at an inpatient rehab unit to facilitate titration of their baclofen dose (usually each dose adjustment is followed by 24 hours of observation to assess effect) and for them to adjust to their new level of tone in a way that allows ambulation. Where appropriate, it may be reasonable to discuss inpatient rehabilitation options with patients in the preoperative setting. This allows planning and appropriately sets patient expectations.
Of course, each patient has different operative needs, but this section provides a general description of the operative steps for baclofen pump and spinal catheter implantation.
Generally, patients are positioned in the lateral decubitus position on a bean bag, with the operative side up (Figure 1). It is important to place an axillary roll under the rib cage to minimize the risk of compressive brachial plexus injury. The axilla is palpated to ensure that there is no pressure on the brachial plexus. Close attention is directed to the fibular head and greater trochanter of the femur on the downside to ensure that these structures are well padded. The down arm is padded to minimize pressure on the ulnar nerve. A pillow is placed between the legs and between the arms, which are extended in front of the patient. Fluoroscopy is used to guide needle placement and catheter positioning. The fluoroscopy unit is draped out such that it can perform anterior-posterior and lateral x-rays, with the image intensifier and monitors placed on the abdominal side of the patient (Figure 2).
Incision lines are marked out on the back and on the abdomen. The incision line on the back is paramedian, approximately 5 cm long and centered at a spinal level approximately 2 levels below the desired entry point for the spinal catheter. A paramedian incision is preferred, so the spinous processes can be avoided on the entry trajectory. The incision is centered 2 segments below the proposed spinal catheter entry level to allow the surgeon to approach the entry level, with a shallow angle facilitating the rostral placement of spinal catheter and allowing it to make a gentle turn as it is tunneled over to the abdomen.
The incision line on the abdomen is approximately 2 finger breadths below the costal margin and approximately 10 cm long. After the patient is positioned, the operative sites and the upside flank are carefully prepared.
Creation of the Subcutaneous Pocket for the Pump
Starting with an incision, 2-finger breadths below the costal margin, the surgeon dissects down to the abdominal fascia using monopolar cautery. It is important to dissect all the way down to the fascia, if possible, because the pump must be anchored to this tough layer with nonabsorbable sutures to prevent the pump from migrating or flipping. Once hemostasis is ensured, a moist lap sponge is placed in the subcutaneous pocket, with the tail of the sponge protruding from the incision. Opening of the pocket before placement of the spinal catheter allows a minimal loss of cerebrospinal fluid before pump connection and also acts to minimize manipulations once the spinal catheter is in place.
Placement of the Spinal Catheter
The paramedian incision centered at L4-L5 is opened, and the surgeon dissects down to the lumbar fascia. Under fluoroscopic guidance, the Tuohy needle is inserted normally with an entry point in the L2-L3 region. The angle of attack for the needle is relatively shallow, and this facilitates advancement of the catheter (Figure 3). After the needle enters the subarachnoid space, bevel up toward the operative side, the bevel then is reoriented to face rostrally. Using fluoroscopic guidance, the intrathecal catheter is advanced to the low cervical level if upper and lower extremity symptoms are to be treated and to the midthoracic spine if only treatment of the lower extremity symptoms is desired (Figure 4). When the appropriate catheter position is ensured, the guidewire is removed from the catheter, and an anchoring devise is threaded over the end of the catheter down to the lumbodorsal fascia. The anchor is deployed onto the catheter and sutured down with nonabsorbable suture.
Placement of the Pump and Connection to the Spinal Catheter
From the spinal incision, a short shunt passer is used to tunnel the spinal catheter around to the abdominal incision and it is connected to the pump using a short, sutureless connector. The pump is anchored in the subcutaneous pocket using nonabsorbable sutures, and a side port tap is performed to verify patency of the spinal catheter with good cerebrospinal fluid flow. Both wounds are closed in layers, and the skin is closed.
Patients undergoing placement of a new pump or revision of a spinal catheter are generally hospitalized overnight to ensure there are no untoward effects of the new intrathecal infusion that could lead to respiratory depression. Anteroposterior and lateral postoperative x-rays are obtained to provide a baseline record of pump and catheter position. Intrathecal baclofen therapy is initially started at a low rate, 50 μg/day, in simple continuous mode. Patients then are assessed for their level of tone or dystonic symptoms in the coming weeks, and the baclofen dose is titrated up in an effort to maximize their symptom control and minimize side effects. Many surgeons work with a multidisciplinary team that includes rehabilitation specialists who assist in adjusting the intrathecal dosing, as they see the patients over successive postoperative visits. In patients who are marginally ambulatory, they may struggle with ambulation in the postoperative period until they acclimate to their new level of tone. For these patients, a short stay in an inpatient rehabilitation facility, staffed with personnel who can adjust their intrathecal dose, is very helpful.
Complications of intrathecal baclofen therapy can be grouped into categories as follows: infection, catheter failure, pump failure, and inappropriate medication dosing. Any complication that results in acute loss of intrathecal baclofen therapy must be taken very seriously. Patients who experience abrupt withdrawal of baclofen therapy may have symptoms of rebound spasticity, itching, autonomic instability, seizures, delirium, and others. These patients should be admitted to hospital for close monitoring and treatment of their withdrawal symptoms with valium and oral baclofen. In the immediate postoperative period, it is also necessary to observe the patient for signs of cerebrospinal fluid leaking. Some of these patients present with clear fluid leaking from the spinal incision or accumulating around the pump. Others present more insidiously with positional headaches. In some cases a blood patch is required. Rarely, revision of the spinal incision or a purse string stitch in the fascia around the catheter is required.
Of all complications, infection is one of the most common. To minimize infection risk, practitioners must be meticulous in their surgical technique and in accessing the pump for refills. It is a good practice to dose within 1 hour before incision for any surgical procedure. In addition, the surgeon should try to ensure that the patient has an adequate nutritional status before placing a pump, as this or uncontrolled diabetes may increase infection risk. If an infection occurs, it is necessary to remove the pump and the spinal catheter and start IV antibiotics in consultation with an infectious disease specialist. The pump can be replaced when the erythrocyte sedimentation rate and the C-reactive protein levels normalize and patients have finished their antibiotics.
Catheter failure can occur due to occlusion, disconnection, fracture, or the formation of loculating membranes around the catheter, preventing the drug from circulating freely in the intrathecal space. A side port tap of the pump often demonstrates no cerebrospinal fluid flow if the catheter has failed. If loculating membranes that prevent the medication from reaching the intrathecal space freely are suspected, it may be necessary to inject preservative-free contrast through the side port, thereby performing a pump myelogram. Always make sure that the catheter has been cleared of drug by aspiration before injection through the side port, otherwise the patient could receive an inappropriate bolus of the baclofen. Usually, a CT scan is performed with the pump myelogram to ensure good connectivity of the catheter and appropriate distribution in the intrathecal space. If loculations abound then the contrast will tend to layer in focal areas and not quickly diffuse throughout the cerebrospinal fluid. Failed catheters usually require a surgical procedure to replace some portion of the catheter.
Pump failure is less common than either infection or catheter failure. It usually takes the form of a permanent or intermittent stall of the mechanical motor that controls delivery of the intrathecal medication through the catheter. Another possibility is unexpected failure of the pump's battery. In either case, a surgical procedure is required to replace the pump. The service life of most pumps is approximately 7 years, and all should be replaced before reaching the end of service life to prevent medication withdrawal symptoms.
Any patient receiving intrathecal baclofen is at risk for an inappropriate dose of the medication, and this can result in significant complications. Common problems include filling the pump incorrectly (ie, the needle slips out of the fill port when injecting the refill) resulting in loss of therapy; entering the wrong dosing rate in the software; and injecting through the side port without clearing the catheter, resulting in an unexpected bolus of the drug. Patients who receive an overdose of drug may need supportive care such as mechanical ventilation until the medication clears from the system, whereas patients who are underdosed because of a medication error may require withdrawal treatment (oral valium and baclofen) until therapy can be reestablished.
Intrathecal baclofen therapy circumvents the blood–spinal cord barrier and acts as a GABAB agonist, reducing the excitation that Ia muscle spindle afferents exert on α-motor neurons. This mechanism results in significant improvements in spasticity. Placement of the subcutaneous pump and intraspinal catheter proceeds with proper patient positioning, opening of the subcutaneous abdominal pocket, placement of the spinal catheter, and connection of the spinal catheter to the pump. Working with a multidisciplinary team, the patient's intrathecal dose is titrated to improve symptoms of spasticity and to minimize side effects. When used properly to treat an appropriate indication, intrathecal baclofen therapy can greatly improve patient quality of life.
Albright AL, Turner M, Pattisapu JV. Best-practice surgical techniques for intrathecal baclofen
therapy. J. Neurosurg. 2006;104(4 suppl):233–239.
Bilsky GS, Saulino M, O'Dell MW. Does every patient require an intrathecal baclofen
trial before pump placement? Phys Med Rehabil. 2016;8(8):802–807.
Greenberg MS ed. Handbook of Neurosurgery. 8th ed. New York, NY: Thieme; 2016.
Maneyapanda MB, McCormick ZL, Marciniak C, et al Long-term dosing of intrathecal baclofen
in the treatment of spasticity
after acquired brain injury. Phys Med Rehabil. 2017;9(6):556–562.
Saulino M, Anderson DJ, Doble J, et al Best practices for baclofen therapy: troubleshooting. Neuromodulation. 2016;19(6):632–641.
Spader HS, Bollo RJ, Bowers CA, et al Risk factors for baclofen pump infection in children: a multivariate analysis. J. Neurosur Pediatr. 2016;17(6):756–762.
Stevenson VL. Intrathecal baclofen
in multiple sclerosis. Eur Neurol. 2014;72(suppl 1):32–34.
Zuckerbraun NS, Ferson SS, Albright AL, et al Intrathecal baclofen
withdrawal: emergent recognition and management. Pediatr Emerg Care. 2004;20(11):759–764.
Keywords:Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved
Generalized dystonia; Intrathecal baclofen; Spasticity