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

Dose escalation in intrathecal baclofen therapy based on disease etiology: Can an a priori target dose be established? A ten-year follow-up study

CONTEXT

Intrathecal baclofen (ITB) therapy is administered for severe, persistent spasticity that cannot be addressed by oral medication or other treatments.

OBJECTIVE

We aimed to evaluate the target dose of ITB for severe, persistent spasticity based on disease etiology.

METHODS

Data at baseline (discharge), 1, and 10 years from 102 patients who received ITB therapy between 1985 and 2011 were retrospectively collected. Patients were divided based on disease etiology (cerebral, spinal, or multiple sclerosis [MS]) to evaluate differences in dose requirements. A comprehensive literature review of the dose trends in ITB therapy was conducted.

RESULTS

Patients with cerebral spasticity (n = 62) required the highest dose after discharge (102.66 ± 30.9 µg), 1 (402.29 ± 300.2 µg), and 10 years (578.74 ± 421.2 µg). Patients with spinal spasticity (n = 19) required an average of 82.89 ± 30.7 µg baclofen at discharge, 296.3 ± 224.6 µg after 1 year, and 522.63 ± 425.97 µg after 10 years. Patients with MS-related spasticity (n = 21) had a dose of 82.73 ± 39.3 µg baclofen at discharge, 226.95 ± 193.3 µg after 1 year, and 320.6 ± 261.4 µg after 10 years. The differences among the categories were significant after 1 and 10 years of therapy.

CONCLUSIONS

The largest dose escalation occurs within the first year of ITB therapy. Our work provides a guideline for the initial dose setting during the inpatient stay after implantation and potentially expected dosage over the years thereafter, although this must always be adjusted individually.

Body Weight-Supported Treadmill Training Ameliorates Motoneuronal Hyperexcitability by Increasing GAD-65/67 and KCC2 Expression via TrkB Signaling in Rats with Incomplete Spinal Cord Injury

Spasticity is a typical consequence after spinal cord injury (SCI). The critical reasons are reducing the synthesis of Gamma-Aminobutyric Acid (GABA), glycine and potassium chloride co-transporter 2 (KCC2) inside the distal spinal cord. The current work aimed to test whether exercise training could increase the expression of glutamic acid decarboxylase 65/67 (GAD-65/67, the key enzymes in GABA synthesis) and KCC2 in the distal spinal cord via tropomyosin-related kinase B (TrkB) signaling. The experimental rats were randomly assigned to the following five groups: Sham, SCI/phosphate-buffered saline (PBS), SCI-treadmill training (TT)/PBS, SCI/TrkB-IgG, and SCI-TT/TrkB-IgG. After that, the model of T10 contusion SCI was used, then TrkB-IgG was used to prevent TrkB activity at 7 days post-SCI. Body weight-supported treadmill training started on the 8^th day post-SCI for four weeks. The Hmax/Mmax ratio and the rate-dependent depression of H-reflex were used to assess the excitability of spinal motoneuronal networks. Western blotting and Immunohistochemistry techniques were utilized for measuring the expression of GAD-65, GAD-67, and KCC2. The findings revealed that exercise training could reduce motoneuronal excitability and boost GAD-65, GAD-67, and KCC2 production in the distal region of the spinal cord after SCI. The effects of exercise training were decreased after the TrkB signaling was inhibited. The present exploration demonstrated that exercise training increases GAD-65, GAD-67, and KCC2 expression in the spinal cord via TrkB signaling and that this method could also improve rats with motoneuronal hyperexcitability and spasticity induced by incomplete SCI.

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.

Consensus on the appropriate use of intrathecal baclofen (ITB) therapy in paediatric spasticity

Among features of motor disorders in children, spasticity is associated with considerable morbidity and problems in care, particularly in severely affected patients. Intrathecal baclofen (ITB) has been increasingly used as a relatively specific treatment modality for spasticity. To date, most of the evidence for its use in paediatric patients has come from retrospective and uncontrolled studies, although randomised, controlled trials of screening ITB and ITB therapy itself have recently been published. This consensus statement on the use of ITB in paediatric patients with spasticity was developed on the basis of currently available evidence, with the aim of providing information for clinicians, promoting an expert opinion and a consistent approach to the management of these patients and emphasising the need for further prospective, large-scale studies.

Clinical and neurophysiologic assessment of strength and spasticity during intrathecal baclofen titration in incomplete spinal cord injury: single-subject design

BACKGROUND/OBJECTIVE

Spasticity after spinal cord injury (SCI) is commonly managed with oral and intrathecal baclofen (ITB), with less attention to the effects on voluntary motor control. Studies combining clinical and neurophysiologic assessments during dose optimization are rare. Study aims (a) systematically evaluate effects of varied doses of oral and ITB on clinical and neurophysiologic measures of strength and spasticity and (b) relate clinical and neurophysiologic findings.

METHODS

A 41-year-old man with an incomplete T11-ASIA D SCI was studied during ITB titration. Spasticity and strength in the lower extremities were assessed clinically and neurophysiologically at 5 different daily dosages of baclofen: (a) 80 mg oral, (b) 80 mg oral/50 microg ITB, (c) 80 mg oral/125 microg ITB, (d) 30 mg oral/125 microg ITB, and (e) 125 microg ITB only.

RESULTS

A dose-dependent change in the Ashworth score and lower limb motor score was observed during titration of oral and ITB. Whereas the Hoffman (H)-reflex was abolished after the introduction of ITB, the flexion withdrawal reflex approximated a dose-dependent pattern. Changes in the motor score and EMG during voluntary muscle activation were proportionally smaller than the corresponding changes in clinical and neurophysiologic measures of spasticity. Neurophysiologic assessment largely paralleled clinical findings.

CONCLUSIONS

This single-subject study shows that the control of spasticity can be achieved without detrimental effects on strength in incomplete SCI and suggests the need for including strength testing in comprehensive clinical assessment of spasticity. The study shows convergent validity between clinical and neurophysiologic assessments during ITB dose titration. Adding neurophysiologic assessment to clinical assessment may provide objectivity and sensitivity and facilitate decision-making during ITB titration.