Kai Wohlfarth

Botulinum A Toxin Therapy: Neutralizing and Nonneutralizing Antibodies—Therapeutic Consequences ☆

Although muscle-relaxant doses of botulinum A toxin (BoNT/A) are generally lower than doses stimulating the immune system, specific antibodies are raised in a substantial number of patients. As a rule, this necessitates the termination of treatment. Therefore, a reliable determination of specific anti-BoNT/A antibodies is helpful and we introduced, for this purpose, a novel in vitro toxin-neutralizing assay based on a nerve-muscle preparation. We measured the antibody titers in four groups of subjects: Group 1 comprised 75 randomly selected patients of a total of 295 who responded to treatment with Dysport in our local clinic. Five patients, in group 2, were nonresponders. Group 3 consisted of 32 untreated volunteers and group 4 of 8 subjects immunized with a toxoid more than 10 years ago. Two of the responders had marginal titers of neutralizing antibodies, while they were present in all nonresponders. The sera of all responders were also tested for nonneutralizing antibodies by ELISA. Their occurrence, however, was of no consequence to the therapeutic success. The blood samples of volunteers were free from specific antibodies, whereas antibodies persisted in the immunized subjects for longer than a decade. Patients from various clinics who had been treated unsuccessfully with the toxin-14 patients had received BOTOX, 7 had been treated with Dysport, and 7 with both products-all had neutralizing antibodies. Whether there was an antibody response depended on the amount of toxin administered. We believe, however, the effective toxin dose can be reduced by so much as to make antibody production highly improbable.

Botulinum A toxins: units versus units

Abstract We investigated the efficacies and potencies of two commercial preparations of botulinum neurotoxin type A (BoNt/A) reputed to differ in potency. Tests were conducted in vitro using the mouse phrenic nerve-hemidiaphragm which is an approved tool for measuring clostridial toxicity. In addition, in a double-blind trial on volunteers, varying amounts of one product were injected into the Musculus extensor digitorum brevis of the left foot, while equal amounts, i.e. units, of the other preparation were injected into the same muscle of the right foot. Compound muscle action potentials (CMAPs) were recorded before and at various points in time after the injections. As opposed to wide-spread anecdotal reports, no difference in effectiveness was found. The dose-response curves obtained from the mouse organ preparation with both commercial products equalled one another in potency (number of units) and corresponded to previous toxicity tests in mice conducted elsewhere. Dose-response curves from volunteers were also identical for both commercial preparations. The time course of paralysis and recovery of muscle function did not differ either. At lower concentrations of toxin, however, restoration of muscle function was more rapid than at higher concentrations. Since the results obtained from man and the animal organ preparation are in excellent accord, we conclude that 1 unit of Botox corresponds to 1unit of Dysport.

Muscle vibration: Different effects on transcranial magnetic and electrical stimulation

Transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (TES) were applied before and 3 s after onset of vibration (0.5 mm, 80 Hz) of the right extensor carpi radialis muscle in 5 healthy subjects. Vibration induced significant augmentation and latency shortening of motor evoked potentials elicited by TMS, but not TES. This provides evidence for an involvement of cortical mechanisms by muscle vibration in the augmentation of MEPs following TMS.

Neutralizing antibodies and secondary therapy failure after treatment with botulinum toxin type A: much ado about nothing?

Objectives:As the indications and duration of treatment of botulinum toxin type A (BoNT-A) increase, so do reports of patients who fail therapy after initially responding well. Although a loss of efficacy is commonly thought to be associated with neutralizing antibodies (NAbs), this relationship is not strongly correlated, and other factors may play a significant role. To explore this issue, we evaluated levels of NAbs in a large selected cohort of secondary nonresponders to BoNT-A using the highly sensitive mouse phrenic nerve-hemidiaphragm assay. Methods:Serum samples from 503 patients treated with BoNT-A who had a variety of diagnoses were tested for the presence of NAbs. Results:Fewer than half of the patients (n = 224, 44.5%) were found to be NAb-positive, indicating that in more than half of the secondary nonresponders, lack of efficacy is not due to NAb formation. The proportion of secondary nonresponders with NAbs was greater for higher dose indications (focal spasticity and spasmodic torticollis) than for lower dose indications (blepharospasm and hemifacial spasm) and increased with shorter injection intervals. Neutralizing antibody development was independent of the commercial preparation used. Conclusions:Our results indicate that although NAb formation does play a role in secondary treatment failure with BoNT-A, this is not the cause in all patients, and the influence of other factors needs to be investigated. Gaining a better understanding of the underlying mechanisms for secondary treatment failure may help in the prediction, diagnosis, management, and prevention of this problem.

Botulinum A toxin : Dysport improvement of biological availability

We investigated the efficacy and potency of Dysport, a botulinum neurotoxin type A complex approved for therapy, under various conditions. Conditions for maximal expression of biological activity were explored in vitro in the phrenic nerve-hemidiaphragm preparation, while conditions for optimal distribution of the toxin were tested in vivo in a double blind trial involving volunteers, using the foot Muscles extensor digitorum brevis. In contrast to the recommendations of the manufacturer, the biological availability of Dysport could be enhanced by (1) lowering its concentration, (2) supplementing with albumin, and (3) increasing the injection volume. On the basis of these experimental findings Dysport was diluted to a final concentration of 50 U/ml for therapeutic purposes. In a blind, single crossover study patients suffering from various forms of dystonia were treated with Dysport, first diluted and dosed as suggested by the manufacturer and then with doses cut by approximately 70% in accordance with the experimental findings. The low-dose treatment was as effective as the treatment with the recommended higher doses, but side effects were considerably less apparent. The benefits to be derived from these adjustments include a low risk of antibody formation, which could preclude continued or future treatment and substantial cost savings.

Low-Dose Treatment of Cervical Dystonia, Blepharospasm and Facial Hemispasm with Albumin-Diluted Botulinum Toxin Type A under EMG Guidance

Several studies support the hypothesis that low-dose botulinum toxin treatment may be as beneficial as high-dose regimen. Therefore, we studied 115 patients (aged 27–84; mean 58.0, SD = 12.9 years; 68% females, 32% males) suffering from cervical dystonia (n = 66), blepharospasm (n = 28), and facial hemispasm (n = 21) over a period of 2 years in an open label, non-controlled pilot study. Patients received low-dose treatment with botulinum toxin type A (Dysport®). The toxin was diluted in 20 ml of 0.1% albumin solution to arrive at a concentration of 25 MU/ml and injected under EMG control. Patients responded to the treatment about 1 week after injection (mean 7.3 days, SD = 4.6). The mean duration of beneficial effects was 11.7 weeks (SD = 5.6). Patients evaluated the clinical global improvement on a scale ranging from 0 to 4. For the whole population, the mean was 2.7 points (SD = 1.1). In none of the subjects could antibodies to botulinum toxin type A be detected, and only a few side effects were observed. In conclusion, low-dose therapy with botulinum toxin A merits further controlled studies.

Remote F-wave changes after local botulinum toxin application.

OBJECTIVE Although the therapeutic effects of botulinum toxin A can be explained by its action at the neuromuscular junction, central or more proximal effects have also been discussed. METHODS Eleven patients with torticollis spasmodicus and 3 patients with writers cramp were studied before and 1 and 5 weeks after the first treatment with botulinum toxin. We measured compound muscle action potentials (CMAPs), motor conduction velocities (MCVs), the shortest (SFL) and the mean F-wave latencies (MFL) and F-wave persistence (30 trials) of untreated muscles for each side (ulnar nerve-abductor digiti minimi muscle, peroneal nerve-tibialis anterior muscle). RESULTS CMAPs and MCVs showed no significant changes. For both nerves, however, SFL and MFL were prolonged slightly 1 week after treatment and returned to about baseline after 5 weeks (t test). The F-wave persistence was reduced 1 week after treatment for the right ulnar and both peroneal nerves (t test). CONCLUSIONS These results are not likely due to an impairment of neuromuscular transmission. Instead, we propose a decreased excitability of alpha-motoneurons supplying non-treated muscles. A reduction of muscle spindle activity or changes of the recurrent inhibition are discussed as possible causes.

Muscle fatigue, lactate, and pyruvate in mitochondrial myopathy with progressive external ophthalmoplegia

We studied muscle fatigue and serum lactate and pyruvate levels in 20 patients with mitochondrial myopathy with progressive external ophthalmoplegia (PEO). Fatigue was assessed in the adductor pollicis muscle (AP) using a low‐intensity exercise protocol (20 min). Forces (TFs) and relaxation times of ulnar nerve evoked twitches, compound muscle action potentials (CMAPs), and maximal voluntary contractions (MVCs) were monitored. Serum lactate and pyruvate levels were independently measured at rest and after exercise on a bicycle (15 min, 30 W). Most patients showed abnormal fatigue of the AP with a reduction of TFs and MVCs and normal CMAPs. The reduced TFs were significantly correlated with lactate levels at rest (r = −0.60, P < 0.05) and less so with those after exercise (r = −0.47, P < 0.05). Pyruvate levels revealed a similar correlation although they were widely scattered. We conclude that abnormal fatigue in PEO is metabolic, is localized beyond the muscle fiber membrane, and involves the electromechanical coupling and the contractile apparatus. Serum lactate levels at rest are good predictors of fatigue in PEO.

Neutralizing botulinum toxin type a antibodies: clinical observations in patients with cervical dystonia.

Neutralization of antibodies poses a problem for a substantial number of cervical dystonia (CD) patients treated with botulinum toxin type A (BoNT/A). Presence of these antibodies may lead to a secondary nonresponse to BoNT/A treatment. In this study, we compared 6 antibody-positive (Ab+) with 12 antibody- negative (Ab-) CD patients treated with BoNT/A (Dysport) and matched for du- ration of treatment, number of BoNT/A injections, and severity of clinical symptoms. The two groups differed in cumulative BoNT/A dose (Ab+, 5984 mouse units [MU ], SD = 3151 MU; Ab-, 3143 MU, SD =1294 MU; P <.05), in addition, ab+ patients were significantly younger (ab+ mean age = 41.3 y, sd =5.9 y; ab - mean age = 56.8 y, sd = 15.3 y; p <.05), in or- der to avoid formation of neutralizing antibodies, doses of bont/a should be kept as low as possible, the risk of antibody formation seems to be higher in younger patients.

Acamprosate Reduces Motor Cortex Excitability Determined by Transcranial Magnetic Stimulation

Acamprosate is effective in reducing alcohol intake in weaned alcoholics. We were interested if acamprosate had an effect on the excitability of cortical motoneurons determined by transcranial magnetic stimulation (TMS). We studied 12 male healthy volunteers (mean age 29.5 years, SD = 4.8) who were either treated with 6 tablets of acamprosate (each containing 333 mg verum) per day or placebo (randomized cross-over design) for 1 week. TMS was performed after each treatment session including a paired stimulation paradigm. Motor evoked potentials (MEPs) of the placebo and verum group did not differ with respect to paired stimulation. However, motor threshold increased in the acamprosate group (verum: 61.5% (SD = 7.9) vs. placebo: 58.9% (SD = 8.8), p = 0.036). We conclude that acamprosate leads to a hypoexcitability of the motor cortex. This might be due to subcortical mechanisms, e.g. thalamocortical pathways since intracortical inhibition and facilitation was not affected.