Introduction

Intrathecal baclofen therapy (IBT) has been used for 3 decades in the management of spastic hypertonia associated with the upper motor neuron syndrome ( ). This chapter will describe patient selection, initial trialing, management of the newly implanted patient, chronic maintenance therapy, and management of intrathecal (IT) baclofen overdose and withdrawal. As of 2016 only one manufacturer (Medtronic) has United States Food and Drug Administration (FDA) approval for chronic IT baclofen infusion. Recognizing this, the chapter focuses on management of the Medtronic system while acknowledging that the principles of management would likely be similar with other systems with relatively minor differences in technical application ( ).

Patient Selection

IBT is formally indicated for the management of severe spasticity of spinal and cerebral origins. Prior to delving into the details of patient selection, it is a worthwhile exercise to define formally spasticity and severe spasticity. Despite its ubiquity, spasticity is a challenging entity to delineate with an evolving definition. Perhaps the best description that captures the depth and breath of this phenomenon is “a disordered sensorimotor control, resulting from an upper motor neuron lesion, presenting as intermittent or sustained involuntary activation of muscles” ( ). This definition shifts the focus away from measurement of stiffness to the measurement of the abnormal muscle activity. Thus terms such as clonus, cocontraction, associated reaction, dystonia, and spasms are included in this spasticity definition but are potentially omitted with other attempts at explanations. This description attempts to exclude the negative sign of muscle weakness associated with the upper motor neuron syndromes, as well as the changes in the rheologic properties of soft tissue ( ). The disease processes classically associated with this phenomenon are clearly divergent. Ultimately the word spasticity likely represents an umbrella term for a multiplicity of movement disorders. Clinicians must recognize the limitations of the term spasticity when considering intrathecal baclofen or any other spasticity-modulating therapy.

The next level of medical decision-making for spasticity management is to determine the gravity of the condition. It is reasonable to consider what the term “severe” implies, despite the vagaries of the spasticity definition described above. Colloquial definitions of severe include terminology such as “causing discomfort or hardship” as well as “very painful or harmful.” It is certainly reasonable to consider spasticity as severe when it is problematic, interfering with comfort, function, or caregiving. Spasticity intensity should include both the clinician’s impression and the patient’s perception. Clinicians should consider how problematic the spasticity is to the patient/caregiver, rather than solely relying on a numerical rating of a particular spasticity assessment measure. For example, modest resistance to passive motion, which could be evaluated as mild to the physician, may have a significant functional impact for the patient, who could describe the same phenomenon as severe. Even mild degrees of spasticity can lead to an inability to perform basic activities of daily living, including hygiene, dressing, and toileting. In addition, involuntary movement and spasms can cause pain, interrupt sleep, negatively impact mood, and impair mobility. These considerations are paramount when contemplating spasticity-reduction techniques ( ).

Spasticity can be both beneficial and deleterious. Advantageous effects of spasticity potentially include assistance with mobility, maintenance of posture, improvement of vascular circulation, preservation of muscle mass and bone mineral density, prevention of venous thrombosis, and assistance in reflexive bowel and bladder function. Conversely, spasticity can interfere with positioning, mobility, comfort, and hygiene. Spasticity has also been linked to increased metabolic demands, which can be problematic in the nutritionally compromised patient. Spontaneous spasms can interfere with sleep or duration of wheelchair use ( ). Spasms can also lead to skin breakdown because of shearing effects or impaired healing of surgical wounds due to tension along suture lines. Clinicians must consider all aspects of a patient’s spasticity before embarking on a treatment plan. The goal may not be complete elimination of spasticity, but rather titration to maximize the risk/benefit ratio.

Hypertonia, a condition marked by an abnormal increase in muscle tension and a reduced ability of a muscle to stretch, can be evaluated clinically using a number of well-established rating scales ( ). The most commonly utilized scales include the Ashworth ( ), Modified Ashworth ( ), and Tardieu ( ), summarized in Table 72.1 . The interrater and intrarater reliability of these scales is generally considered fair to good, with occasional reports of suboptimal consistency ( ). One potential criticism of the Ashworth and Modified Ashworth scales is their inability to distinguish between the rheologic properties of the soft tissues and the neural contributions to hypertonia. In this setting, rheology is defined as the study of deformation of materials. The Tardieu scale attempts to address the difficulty by measuring two angles: the angle (R1) at which resistance is first encountered with a quick muscle stretch, and the final angle (R2) which reflects the maximum range of movement with a slow muscle stretch. The difference between the two is claimed to represent the true amount of spasticity or spasticity angle. More sophisticated measures of hypertonia include neurophysiologic testing that attempts to quantify the muscle response to stretch (surface electromyographic activity, H-reflex response, the H-reflex standardized to the M-wave max, or the F-wave response) or instrumented measurements of stiffness and torque with accelerometers ( ). Some subjective measures include patient assessment of spasm intensity and/or logs of spasm frequency. There is an inconsistent correlation between subjective report and objective measures of spasticity ( ).

Given the diversity of spasticity presentations and the variety of diseases that create spasticity, it is not unexpected that there are a multiplicity of treatment options. These therapeutic modalities can be divided into nonpharmacologic, oral agents, chemodenervation techniques, IT therapy, orthopedic surgical techniques, and neurosurgical interventions ( ). A detailed review of each of these modalities is beyond the scope of this chapter, but Table 72.2 summarizes the nature of each intervention with their associated advantages and disadvantages. How each of these techniques is applied to each patient population is an evolving art and science. The role of IBT within the armamentarium of spasticity modification continues to evolve and define itself.

An important differentiation to be recognized by managing clinicians is severe spasticity, which is a dynamic process amenable to IBT, and contracture, which is a static occurrence that is unresponsive to IBT. Contracture is primarily managed by orthopedic interventions ( ). Distinguishing between these two entities may be impossible on routine clinical examination. An IBT trial may be a useful technique in determining to what degree each phenomenon is present. For patients who demonstrate both contracture and spasticity, there is a suggestion that treatment of spasticity should be undertaken first, followed by orthopedic lengthening or release ( ).

Patient Selection for IBT

Patient selection and education are fundamental concepts to all aspects of medical practice. These principles are of enhanced importance with interventional procedures involving implantable technology. Appropriate candidates for IBT need to be counseled before proceeding with this form of therapy. Patients should be apprized of all aspects of the therapy, including trialing, implantation, postoperative rehabilitation, and chronic maintenance issues. The importance of recognition by the patient and caregivers that this treatment modality represents a long-term commitment cannot be understated. In general, patients can be considered candidates for IBT when:

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  spasticity is poorly controlled despite maximal therapy with other modalities;

  
  
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  spasticity is poorly controlled because of limited patient tolerance of other modalities;

  
  
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  adjustable spasticity reduction afforded by a programmable variable-flow pump or implantable drug delivery system (IDDS) would be advantageous.

The FDA-approved diagnoses for IBT include spasticity of spinal (traumatic spinal cord injury and multiple sclerosis) and cerebral origin (acquired brain injury, cerebral palsy, and stroke). There is greater experience with spasticity of spinal origin when compared to cerebral origin, since the former indications had earlier FDA approval. Other diseases, such as degenerative conditions of the brain and spinal cord (i.e., amyotrophic lateral sclerosis, hereditary spastic paraparesis), have also responded well to IBT ( ).

Patients should be clinically stable, comprehend the advantages and disadvantages of IBT, be able to return to clinic for titration and refills, and have demonstrated a positive response to a test dose of IBT. For individuals with cognitive impairment and in pediatric patients, caregivers of the patient must be involved in the medical decision-making. Traditionally a sufficient amount of time after a neurological insult should pass before considering IT therapy, allowing a reasonable amount of natural recovery to occur. For multiple sclerosis patients, where the neurologic presentation may vary, patients should not be solely evaluated during an exacerbation. In selected circumstances this therapy can be considered early in the postinjury recovery period (e.g., <12 months ). IBT generally reduces lower-limb hypertonia to a greater extent than in upper extremities. Perhaps more cephalad catheter tip placement can potentially improve upper-limb response ( ), although the upper-limb response to this strategy is not uniform ( ). Other advantages of IBT include higher potency with potentially less adverse effects when compared to oral baclofen, the ability to have a global effect on all affected limbs, and the possibility of later adjustment with changing patient needs or progressive disease ( ). Disadvantages include surgical risks (bleeding, infection, damage of neural structures), the potential for serious adverse effects, including overdose and withdrawal, and the requirement for ongoing follow-up with healthcare professionals for dosing adjustments and pump refills. Ventricular shunting for hydrocephalus is not a contraindication to IBT, but practitioners should be aware of potential interactions between the devices on cerebrospinal fluid (CSF) flow ( ). IBT can also be used in patients with seizures, with the understanding that this therapy has been occasionally associated with an increased risk of seizures ( ). Similarly, prior abdominal or pelvic surgery (gastrostromy, suprapubic tube placement, etc.), which is relatively commonplace in neurologic patients, does not represent a contraindication for IBT but does require some consideration during surgical placement ( ). Patients and caregiver should be fully apprized of these issues to make sound decisions in proceeding toward an IT trial.

IBT Trialing

The typical method for IBT trialing is to perform a lumbar puncture and inject a bolus of a baclofen solution into the CSF. Fifty micrograms is the most commonly used initial screening dose ( ). The onset of clinical effects from a screening bolus occurs within 1–3 h postinjection, and peak effects are typically observed 4–6 h postinjection. The effects of the screening bolus are always temporary, with the effects routinely lasting 6–8 h ( ). Prolonged effects of a single test bolus have been reported ( ). Screening boluses can be repeated if the initial injection is unsuccessful. It is commonly accepted practice to wait at least 24 h before repeating a trial to ensure that the patient’s neuromuscular status has completely returned to baseline. “Positive” responses are reported in 80%–90% of bolus trials ( ). Generally, antibiotic prophylaxis is not needed for a bolus trial ( ). For patients on antiplatelet or anticoagulant therapy, recommendations from the American Society of Regional Anesthesia are followed ( ). As a brief summary, antiplatelet or anticoagulant therapy should be halted prior to trialing, with the length of discontinuance varying from hours to days depending on the agent. Fluoroscopic guidance can assist needle localization into the IT space, since anatomic landmarks for lumbar puncture can be variable ( ) and there is the possibility of low CSF flow in this patient population. More recently, ultrasound has been introduced as a possible localization technique ( ).

During the trial phase for IBT some individuals may experience excessive muscle tone reduction, which uncovers latent weakness or aggravates weakness. Should weakness be observed during the screening trial, it should be interpreted in light of the patient’s goals and residual motor skills. For some patients who are nonambulatory, uncovering underlying weakness may be tolerated if IBT can effectively control other more bothersome problems, such as painful spasms or difficulty in rendering perineal care due to excessively spastic hip adductors and flexors. The occurrence of weakness is not always a contraindication for IDDS implantation, since the chronic infusion system has the ability to modulate doses and subsequent desired effects. The reemergence of active movement and motor control in spite of weakness during the screening trial is an indication of later potential improvement through a rehabilitation program, highlighting core and limb strengthening and motor control retraining. Should the weakness be too concerning, options are to repeat the screening trial using a 25 μg bolus of baclofen or a continuous catheter trial (discussed below). The above scenario should be fully reviewed with the patient and/or caregivers prior to executing the trialing procedure.

An alternative method for conducting trials involves placement of a temporary (or permanent) IT catheter and monitoring patient response to a short-term continuous IT infusion of baclofen. If the catheter is intended to be permanent for trial and long-term infusion, it must be surgically internalized and connected to an intervening externalized catheter for external infusion by an external pump. This technique is more commonly utilized for evaluating chronic pain patients for IT therapy. The potential advantages of catheter IBT trials include avoidance of sequential lumbar punctures; presumably improved approximation of chronic postimplant IT infusion response when compared to single bolus injections; the ability to control catheter tip placement; and the ability to adjust infusion rate while assessing favorable (and unfavorable) effects of IBT administration. The disadvantages of catheter trials include increased technical difficulty, increased need for observation, and increased risk of infection, including meningitis and structural damage ( ). The technique for temporary IT catheter placement is similar to the technique for implanting a permanent IT catheter except that the catheter is externalized and connected to a temporary external pump ( ). Fluoroscopic guidance is generally considered mandatory for catheter placement. While antibiotic prophylaxis is usually not needed for bolus trials, it is generally utilized for short-duration IT catheter trials ( ). Factors to consider include the duration of the trial, patient immunocompetency, and potential chronic bacterial colonization. Evidence suggests that trial duration is a key risk factor for development of infectious complications. Thus the trial should last only as long as required to indicate a potential benefit of chronic IBT ( ). There is no consensus regarding the optimal method of anesthesia utilized for catheter placement. Local anesthesia potentially lowers the risk of inadvertent damage to neural structures. However, if excessive patient movement or severe anxiety is anticipated, deep sedation or general anesthesia may be warranted ( ).

There may be rare circumstance when it may be reasonable to consider proceeding to implantation of IDDS without executing a trial ( ). Examples might include uncooperative or behaviorally impaired patients, patients with significant anesthesia risk, anticoagulated patients who have an excessive risk of recurrent thrombosis when off anticoagulation, and patients with problematic lumbar spine anatomy. In these patients a two-stage procedure (trial and implant) can be performed at the same time. The patient must be positioned in the lateral decubitus position so that the IT catheter and IDDS can be implanted without repositioning and redraping the patient. A direct-to-implant approach without trial was described by Borowski et al. In this study, 26 pediatric patients were directly implanted with an IDDS followed by immediate commencement of IBT. These patients had an inaccessible IT space, and underwent simultaneous IDDS implant and posterior spinal fusion for scoliosis. The positive outcomes of this cohort are identical to those of patients who underwent a trial without a concomitant increase in complications ( ). Patient education and counseling are of heightened importance when considering implanting a permanent IDDS without a preceding trial.