Time course of the effect of a bolus dose of intrathecal baclofen on severe cerebral spasticity

Knee Muscle Stretch Reflex Responses After an Intrathecal Baclofen Bolus in Neurological Patients With Moderate-to-Severe Hypertonia

OBJECTIVES

To examine the prevalence, onset threshold, and response magnitude of stretch reflex response (SRR) in the knee extensors and flexors before and after an intrathecal baclofen (ITB) bolus injection in patients with moderate-to-severe hypertonia.

MATERIALS AND METHODS

SRRs were elicited by reciprocal passive knee extension/flexion movements at preset angular velocities of 5, 60, 120, 180, 240, and 300°/s using an isokinetic dynamometer and recorded with surface electromyographic (EMG) electrodes placed over the knee extensors and flexors in 53 neurologic patients before and at 2.5 and 5 hours after an ITB injection via lumbar puncture. Outcome measures included the number of patients with presence/absence of SRRs, the number of SRRs per session, SRR onset threshold angle and velocity, and response magnitudes (peak EMG and area under the EMG curve) for each muscle. Pre-post comparisons were completed using the Fisher's exact and Wilcoxon signed rank tests.

RESULTS

For both knee extensors and flexors, the proportion of patients with present SRRs (p < 0.0001) and the number of SRRs per session (p ≤ 0.027) decreased from pre- to post-ITB. The threshold velocity significantly increased post-injection in both muscles (p ≤ 0.001) without significant changes in the threshold angle. The response magnitudes significantly decreased in the knee extensors (p ≤ 0.016) but not the knee flexors after the injection.

CONCLUSIONS

The prevalence and threshold velocity of SRR emerged as the most robust and practical parameters for assessing hyperreflexia during ITB bolus trial that can complement clinical assessment of muscle hypertonia.

A numerical investigation of intrathecal isobaric drug dispersion within the cervical subarachnoid space

Intrathecal drug and gene vector delivery is a procedure to release a solute within the cerebrospinal fluid. This procedure is currently used in clinical practice and shows promise for treatment of several central nervous system pathologies. However, intrathecal delivery protocols and systems are not yet optimized. The aim of this study was to investigate the effects of injection parameters on solute distribution within the cervical subarachnoid space using a numerical platform. We developed a numerical model based on a patient-specific three dimensional geometry of the cervical subarachnoid space with idealized dorsal and ventral nerve roots and denticulate ligament anatomy. We considered the drug as massless particles within the flow field and with similar properties as the CSF, and we analyzed the effects of anatomy, catheter position, angle and injection flow rate on solute distribution within the cerebrospinal fluid by performing a series of numerical simulations. Results were compared quantitatively in terms of drug peak concentration, spread, accumulation rate and appearance instant over 15 seconds following the injection. Results indicated that solute distribution within the cervical spine was altered by all parameters investigated within the time range analyzed following the injection. The presence of spinal cord nerve roots and denticulate ligaments increased drug spread by 60% compared to simulations without these anatomical features. Catheter position and angle were both found to alter spread rate up to 86%, and catheter flow rate altered drug peak concentration up to 78%. The presented numerical platform fills a first gap towards the realization of a tool to parametrically assess and optimize intrathecal drug and gene vector delivery protocols and systems. Further investigation is needed to analyze drug spread over a longer clinically relevant time frame.

Reliability of the Modified Tardieu Scale and the Modified Ashworth Scale in adult patients with severe brain injury: a comparison study

Objective: To assess and to compare the reliability of the Modified Tardieu Scale with the Modified Ashworth Scale in patients with severe brain injury and impaired consciousness.

Design: Cross-sectional observational comparison study.

Setting: An early rehabilitation centre for adults with neurological disorders.

Subjects: Thirty patients with impaired consciousness due to severe cerebral damage of various aetiologies.

Measurement protocol: Four experienced physical therapists rated each patient in a randomized order once daily for two consecutive days. Shoulder, elbow, wrist, hip, knee and ankle spasticity were assessed by the use of Modified Tardieu Scale and Modified Ashworth Scale data collection procedures.

Main outcome measures: Test - retest and inter-rater reliability (k=kappa value) of the Modified Tardieu Scale and the Modified Ashworth Scale.

Results: The test-retest reliability of the Modified Ashworth Scale was moderate to good (k = 0.47-0.62) and of the Modified Tardieu Scale moderate to very good (k = 0.52-0.87). Test - retest reliability was significantly higher within the Modified Tardieu Scale in comparison with the Modified Ashworth Scale (Z<1.96; p<0.05) except for shoulder extensor and internal rotator muscles (Z<1.96; p<0.05). Although inter-rater reliability of both scales was poor to moderate (Modified Ashworth Scale: k = 0.16-0.42; Modified Tardieu Scale: k = 0.29-0.53), significantly higher k-values were revealed with the Modified Tardieu Scale for all tested muscle groups (Z<1.96; p<0.05) except for wrist extensors (Z<1.96; p<0.05).

Conclusion: In patients with severe brain injury and impaired consciousness the Modified Tardieu Scale provides higher test-retest and inter-rater reliability compared with the Modified Ashworth Scale and may therefore be a more valid spasticity scale in adults.

Effect of Intrathecal Baclofen Bolus Injection on Ankle Muscle Activation During Gait in Patients With Acquired Brain Injury

Background. Intrathecal baclofen (ITB) bolus injection effectively decreases spinal excitability but the impact on lower limb muscle activation during gait has not been thoroughly investigated. Objective. Examine activation of medial gastrocnemius (MG) and tibialis anterior (TA) muscles during gait before and after ITB bolus injection in patients with resting hypertonia after acquired brain injury. Methods. Lower extremity Ashworth score, temporospatial gait parameters, characteristics of the linear relationship between electromyogram (EMG) and lengthening velocity (LV) in MG during stance, and the duration and magnitude of TA-MG coactivation were assessed before and at 2, 4, and 6 hours after a 50-µg ITB injection via lumbar puncture in 8 hemorrhagic stroke and 11 traumatic brain injury subjects. Results. Temporospatial gait parameters did not significantly differ across the evaluation points ( P ≥ .170). However, Ashworth score ( P < .001), frequency and gain of significant positive EMG-LV slope ( P ≤ .020), and duration of TA-MG coactivation ( P ≤ .013) significantly decreased in the more-affected leg after ITB bolus. EMG changes were not significantly different between patients who did (n = 10) and did not (n = 9) increase gait speed after the injection. The timing of the largest decrease in Ashworth score and the largest decrease in EMG parameters coincided in 36% of cases, on average. Conclusions. ITB bolus injection alters the activation of MG and TA during gait. However, the changes in muscle activation are not closely related to the changes in gait speed or resting muscle hypertonia. The analysis of ankle muscle activation during gait better characterizes the response to ITB bolus injection than gait kinematics.

Differential effect of baclofen on cortical and spinal inhibitory circuits

OBJECTIVE

The cutaneous silent period (SP) is a spinal inhibitory reflex, which suppresses activity in spinal motor nuclei. Transcranial magnetic stimulation (TMS) elicits a cortical SP, which represents GABA(B) receptor-mediated inhibition of cortical excitability. Baclofen as a strong GABA(B) agonist effectively reduces muscle hypertonia, however, it is not known whether intrathecal baclofen (ITB) may modulate spinal inhibitory circuits.

METHODS

We evaluated clinical and neurophysiological effects of ITB in ten patients with severe spasticity due to spinal cord injury (n = 9) and chronic progressive multiple sclerosis (n = 1). Neurophysiological assessment included H reflex and cutaneous and cortical SPs, before and 15, 30, 60, 90, 120, and 180 min after ITB bolus administration.

RESULTS

ITB suppressed soleus H reflex as early as 15 min after lumbar bolus injection; MAS scores declined after 1 h. Cortical SP end latency and duration increased progressively with a significant maximum 3h following ITB bolus, whereas cutaneous SP latency and duration did not change significantly.

CONCLUSION

The present findings suggest that baclofen does not affect the cutaneous SP, but prolongs the cortical SP.

SIGNIFICANCE

The spinal inhibitory circuitry of the cutaneous SP is not modulated by GABA(B) receptor-mediated activity, in contrast to the cortical inhibitory circuitry of the cortical SP, which is subject to powerful GABA(B) control.

Clinical measurement of limb spasticity in adults: state of the science

Spasticity is a neuromuscular dysfunction characterized by tight or stiff muscles. Spasticity occurs across the spectrum of upper motor neuron disease and complicates the course and quality of life of those affected. Accurate and precise assessment of spasticity is the first step in providing safe and effective treatments to patients for management of spasticity. Examiner evaluations (Ashworth Scale, Modified Ashworth, and Visual Analog Scale) and patient self-reports (Visual Analog Scale and Numeric Rating Scale) are used to assess spasticity in clinical practice. We reviewed the biology of spasticity and summarized research that assessed properties of scores obtained from clinical scales when used in a variety of upper motor neuron diseases. The definition of spasticity was inconsistent. Rater reliability or agreement on clinical scales varied widely. Correspondence with electromyogram results was mixed. There was dissimilarity in patient reports and examiner assessments. Scores from clinical scales are responsive (decrease after initiation of treatment with known effectiveness), but the utility of scores for indexing individual change associated with the natural history of upper motor neuron disease is unknown. Future research incorporating patient reports and examiner findings over time will help to clarify the definition and capture the essence of spasticity.

Contractures and involuntary muscle overactivity in severe brain injury

PRIMARY OBJECTIVE

The aim of the present study was to evaluate the association of contractures with an increase or reduction of non-spastic muscle overactivity due to severe cerebral damage.

METHODS AND PROCEDURES

Forty-five patients with tetraparesis after severe cerebral damage were investigated. Three groups were defined based on the presence of spasticity (revealed as resistance to passive stretch (= hypertonia)), and the presence of contracture of the relevant knee joint: Group(s) (17 patients with hypertonia without contracture), Group(s+c) (20 patients with hypertonia and contracture), and Group(c) (eight patients without hypertonia and with contracture). In all groups spontaneous involuntary muscle activity was assessed continuously over a 12-hour period through isometric measurement of knee joint flexion torque. A mathematical algorithm differentiated an hourly muscle activity spectrum (PI(h)). The frequency of peaks (peaks(h)) from the activity spectrum was determined.

MAIN OUTCOMES AND RESULTS

We revealed that Group(s) had higher PI(h) and more frequent peaks(h) compared with Group(s+c) and Group(c) (p<0.05). Group(c) had comparable PI(h) and peaks(h) compared with Group(s+c) (p>0.05).

CONCLUSION

The presence of contractures was associated with lower involuntary muscle overactivity in terms of lower PI(h) and less frequent peaks(h), indicating that contractures may be associated with reduced non-spastic positive features of the upper motor neurone syndrome in patients with severe brain damage.

Intrathecal baclofen in the treatment of spasticity, dystonia and vegetative disorders

Baclofen (beta-p-chlorophenyl-GABA) binds to a number of spinal and cerebral sites and depresses the excitability of motor neurons. Intrathecal administration induces much higher CSF concentrations compared to the limited passage through the blood-brain barrier after oral administration. The development of reliable implanted pumps allows long-term intrathecal baclofen treatment (ITB). Baclofen is mainly an antispastic drug and the main indication of ITB is generalized lower limb spasticity in spinal cord injury and multiple sclerosis. The side-effects are due to either drug over-dose or withdrawal and to malfunctions of the implanted device (disconnections of the catheter, infections, etc.). Large numbers of patients have been treated over the past twenty years. More recently, baclofen has been used in the treatment of spasticity of cerebral origin, and in the treatment of other motor disorders, mainly dystonia. The results in cerebral palsy are promising and ITB's role will probably grow in the management of the movement disorders of these children. Further studies are required on the exact site of action, on the possible association with other drugs, especially clonidine and on the development of sustained release formulations.

Intrathecal baclofen in current neuromodulatory practice: established indications and emerging applications

Intrathecal baclofen (ITB) has evolved into a standard treatment for severe spasticity of both spinal and cerebral origin. The accumulated promising data from reported series of patients receiving ITB therapy together with the fact that spastic hypertonia commonly coexists with other neurological disorders have constituted a solid basis for offering this kind of treatment to patients suffering from other movement disorders. These include motor disorders such as dystonia, amyotrophic lateral sclerosis, status dystonicus, Hallervorden-Spatz disease, Freidreich's ataxia, "stiff-man" syndrome, but also vegetative states after revere brain trauma, anoxic encephalopathy or other pathology and more recently, various chronic pain syndromes. In this article, on the basis of the established applications of ITB therapy, we review the important emerging indications of this rewarding neuromodulation method and attempt to identify its future potential beneficial role in other chronic and otherwise refractory neurological disorders.

Neurophysiological basis and clinical applications of the H-reflex as an adjunct for evaluating response to intrathecal baclofen for spasticity

Implanted programmable pumps that infuse intrathecal baclofen (ITB) markedly enhance the ability of clinicians to manage severe spasticity in appropriately selected patients. Studies addressing the efficacy of this treatment modality have primarily used clinical outcome measures of impairment, particularly reduction in stiffness as measured by the Ashworth scale. Several recent studies, however, highlight comparalively higher sensitivity of neurophysiologic techniques, especially the H-reflex, as an objective index of spinal cord response to ITB administration. We review the conceptual, physiological, and methodological hases for use of the H-reflex as an adjunct to clinical evaluation among patients receiving ITB infusion, including published reports and selected case studies that address the potential advantages and limitations of such techniques when applied to dose titration and system "troubleshooting" scenarios, We also address the implications of such findings in the context of reported complications such as "tolerance" to ITB administration and catheter "microfracture". The accumulated knowledge suggests that H-reflex is a sensitive method for documenting altered spinal cord responsiveness in the presence of ITB delivery. We therefore recommend using H-reflex as an adjunct to clinical evaluation when judging the overall effectiveness of ITB administration.

Dose-response relationship between the H-reflex and continuous intrathecal baclofen administration for management of spasticity

OBJECTIVE

To determine the relationship between the H-reflex (H/M ratio) and continuous intrathecal baclofen (CITB) dose after pump implantation for control of spastic hypertonia.

METHODS

Soleus H-reflexes were serially recorded in 34 subjects (19 men, mean age 32 years, mean follow-up 1.7 years) during simple continuous mode of CITB delivery. Different fitting methods were explored to determine which function best described changes in H/M ratio with increasing CITB dose. We then calculated effective CITB doses yielding H/M ratios equal to 75, 50, and 25% (ED75, ED50, ED25) of the baseline recorded before the implant in 22 subjects.

RESULTS

We found a significant dose-response relationship between the soleus H/M ratio and CITB dose. A two-decay exponential function was the best fit on each side for pooled data, but a general linear model when controlling for subject. The mean ED75, ED50, ED25 were 30, 70, and 110 mcg/day. Logistical regression predicted with high probability that the H/M ratio should be less than 30% at CITB doses above 150 mcg/day.

CONCLUSIONS

H/M ratio is strongly dependent on CITB dose. It sharply decreases up to 150 mcg/day of CITB followed by a plateau.

SIGNIFICANCE

Establishing the relationship between the H/M ratio and CITB dose may be useful for dose titration and early identification of an ITB system malfunction.

Comparison of Clinical and Neurophysiologic Responses to Intrathecal Baclofen Bolus Administration in Moderate-to-Severe Spasticity After Acquired Brain Injury

OBJECTIVES

To compare clinical and neurophysiologic responses to intrathecal baclofen (ITB) bolus injection in subjects with spasticity after acquired brain injury.

DESIGN

Prospective case series.

SETTING

Tertiary care rehabilitation center.

PARTICIPANTS

Thirty consecutive ITB pump candidates with dysfunctional spasticity caused by traumatic brain injury, hypoxic encephalopathy, or stroke.

INTERVENTION

A single 50-microg ITB bolus.

MAIN OUTCOME MEASURES

Lower-extremity Ashworth Scale score at 2, 4, and 6 hours after ITB bolus; soleus Hoffmann reflex (H-reflex)/M-wave amplitude (H/M) ratio and abductor hallucis F-wave persistence and F/M ratio at 5 hours. Nonparametric repeated-measures analysis of variance and paired t test were used for statistical analyses.

RESULTS

The Ashworth score on the more involved side significantly decreased from 2.4+/-0.7 at baseline to 1.5+/-0.6 and 1.4+/-0.6 at 4- and 6-hour evaluations, respectively (P<.001). H/M ratio significantly decreased bilaterally (more involved side, 62%+/-28% to 14%+/-19%; less involved side, 59%+/-26% to 11%+/-20%; P<.001). F-wave persistence significantly decreased on the more involved side (86%+/-17% to 75%+/-13%, P<.05) with no change in F/M ratio. There was no significant correlation among these outcome measures before or after the ITB bolus injection.

CONCLUSIONS

H/M ratio is more sensitive than the Ashworth score or F-wave persistence in detecting a physiologic response to ITB bolus. H-reflex is useful for verification of ITB bolus administration, as an adjunct to clinical evaluation, particularly among patients with moderate spasticity at rest or with small changes in Ashworth score. However, potential application of the marked sensitivity of the H-reflex to other clinically challenging situations, such as early detection of possible ITB system malfunction, awaits further investigation.