Bernhard Voller

Transcranial magnetic stimulation of deep brain regions: evidence for efficacy of the H-Coil

OBJECTIVE Standard coils used in research and the clinic for noninvasive magnetic stimulation of the human brain are not capable of stimulating deep brain regions directly. As the fields induced by these coils decrease rapidly as a function of depth, only very high intensities would allow functional stimulation of deep brain regions and such intensities would lead to undesirable side effects. We have designed a coil based on numerical simulations and phantom brain measurements that allows stimulation of deeper brain regions, termed the Hesed coil (H-coil). In the present study we tested the efficacy and some safety aspects of the H-coil on healthy volunteers. METHODS The H-coil was compared to a regular figure-8 coil in 6 healthy volunteers by measuring thresholds for activation of the abductor pollicis brevis (APB) representation in the motor cortex as a function of distance from each of the coils. RESULTS The rate of decrease in the coil intensity as a function of distance is markedly slower for the H-coil. The motor cortex could be activated by the H-coil at a distance of 5.5 cm compared to 2 cm with the figure-8 coil. CONCLUSIONS The present study indicate that the H-coil is likely to have the ability of deep brain stimulation and without the need of increasing the intensity to extreme levels that would cause a much greater stimulation in cortical regions. SIGNIFICANCE The ability of non-invasive deep brain stimulation potentially opens a wide range of both research and therapeutic applications.

Effects of brain polarization on reaction times and pinch force in chronic stroke

BackgroundPrevious studies showed that anodal transcranial DC stimulation (tDCS) applied to the primary motor cortex of the affected hemisphere (M1affected hemisphere) after subcortical stroke transiently improves performance of complex tasks that mimic activities of daily living (ADL). It is not known if relatively simpler motor tasks are similarly affected. Here we tested the effects of tDCS on pinch force (PF) and simple reaction time (RT) tasks in patients with chronic stroke in a double-blind cross-over Sham-controlled experimental design.ResultsAnodal tDCS shortened reaction times and improved pinch force in the paretic hand relative to Sham stimulation, an effect present in patients with higher impairment.ConclusiontDCS of M1affected hemisphere can modulate performance of motor tasks simpler than those previously studied, a finding that could potentially benefit patients with relatively higher impairment levels.

Treatment of focal hyperhidrosis with botulinum toxin type A: long-term follow-up in 61 patients.

Background The blocking action of botulinum toxin type A (BTX‐A) on cholinergically innervated sweat glands has been used successfully to treat patients with focal hyperhidrosis.

Respective Potencies of Botox® and Dysport® in a Human Skin Model : A Randomized, Double-blind Study

Mouse units used to quantify the activity of botulinum A toxin preparations are not equivalent and issues concerning efficacy and safety remain with regard to their respective potencies and diffusion qualities in human tissue. We compared the effects of Botox® (BOT) and Dysport® (DYS) in different doses and dilutions in a human skin model. Eighteen (8 women, 10 men) healthy volunteers, aged 28.4 years ± 5.7 years were injected intradermally with pure saline, BOT and DYS at 16 points in the abdomen in random order and in a double‐blind condition, using two conversion ratios (1:3 and 1:4) and three different dilution schemes. For an objective outcome, the Ninhydrin sweat test was used to compare the anhidrotic areas. Both preparations showed a linear dose and dilution relationship with similar variances of responses for anhidrosis and hypohidrosis, indicating the same reliability of response. The dose equivalence conversion ratios (BOT: DYS) were 1:1.3 for anhidrosis and 1:1.6 for hypohidrosis (1:1.1‐1.5 and 1:1.4‐1.8 95% confidence intervals). The diffusion characteristics of both products were similar. A dose equivalence factor of more than 1:2 (BOT:DYS) is not supported by these objective and reproducible data.

Contralateral hand anesthesia transiently improves poststroke sensory deficits

To test a possible strategy to alleviate somatosensory deficits after stroke.

Safety study of high-frequency transcranial magnetic stimulation in patients with chronic stroke ☆ ☆☆

OBJECTIVE Repetitive transcranial magnetic stimulation (rTMS) is a potential therapeutic tool to rehabilitate chronic stroke patients. In this study, the safety of high-frequency rTMS in stroke was investigated (Phase I). METHODS The safety of 20 and 25 Hz rTMS over the motor cortex (MC) of the affected hemisphere, with intensities of 110-130% of the motor threshold (MT), was evaluated using surface electromyography (EMG) of hand and arm muscles. RESULTS Brief EMG bursts, possibly representing peripheral manifestations of after discharges, and spread of excitation to proximal muscles are considered to be associated with a high risk of seizure occurrence. These events were recorded after the rTMS trains. Neither increased MC excitability nor improved pinch force dynamometry was found after rTMS. CONCLUSIONS Stimulation parameters for rTMS, which are safe for healthy volunteers, may lead to a higher risk for seizure occurrence in chronic stroke patients. SIGNIFICANCE rTMS at rates of 20 and 25 Hz using above threshold stimulation potentially increases the risk of seizures in patients with chronic stroke.

Long-term efficacy and respective potencies of botulinum toxin A and B: a randomized, double-blind study.

Background  Mouse units (mU) are used for quantification of the biological activity of botulinum A and B toxin preparations. However, in human tissue, mU values between preparations are not equivalent and lack of clarity concerning efficacy and safety remains with regard to their respective potencies, duration of drug effect and diffusion qualities.

NEUTRALIZING ANTIBODIES IN DYSTONIC PATIENTS WHO STILL RESPOND WELL TO BOTULINUM TOXIN TYPE A

Kranz et al. used a ninhydrin sweat test (NST) and mouse diaphragm test (MDT) in 14 dystonic patients and 14 controls and reported subclinical neutralizing antibodies (Abs) in patients with “good clinical responses” to BoNT/A. The authors defined the responses based on a three-point decrease on modified-Tsui scale, injected-muscle atrophy, or reported BoNT/A-associated adverse events.1 Only one patient had anti-BoNT/A Abs (1 mU/mL, by MDT) and a marked anhydrotic area reduction (0.26 cm2). Seven other patients had “borderline” titers of either 0.4 or 0.8 mU/mL and reduced anhidrosis area. The study design, small sample size, and subjective clinical-response assessment precludes extension to incidence value (>40%). Mixing Botox- and Dysport-treated patients complicates analysis because these products have different immune-response rates. NST employs area, but neglects color density. NST correlation value was missing, as the anhydrotic area could vary with injection method. Hyperhidrosis effect reproducibility was also overlooked. The Results imply that NST was done with both Botox and Dysport but this contradicts the statement in the Methods that Dysport was the test agent. The observation that patients had different Ab levels after similar toxin doses is expected.2,3 Immune responses mature with time, boosters, and are genetically controlled.2,3 This means that patients responding to treatment would have different Ab levels, even after similar doses and protocols. …

Type of Edema in Posterior Reversible Encephalopathy Syndrome Depends on Serum Albumin Levels: An MR Imaging Study in 28 Patients

The causes of posterior reversible encephalopathy syndrome continue to be debated and other underlying issues are being added to its etiology. In this short and retrospective study, the authors assessed the role of low serum albumin in the development of PRES. The causes of PRES varied and the authors used diffusion-weighted and fluid-attenuated inversion recovery sequences to characterize the edema as vasogenic (N=22) or cytotoxic (N=6). All studies were done within 3 days of the onset of clinical symptoms. Review of laboratory values showed that during this time low serum albumin in 21 of 28 patients was more common and marked in those with vasogenic edema. Although all of this is simple and clear, the role of albumin is sort of like the “chicken and egg” question: Is there more leakage of fluids due to the low albumin, or is it low because it is actively leaking with fluid due to other processes affecting the blood vessel walls? Read the article to find out more! SUMMARY: PRES is a clinicoradiologic entity, combining seizures, blindness, and coma with MR imaging findings of predominantly vasogenic and occasional cytotoxic edema. In this clinical report, we determined the type of edema by using DWI and FLAIR sequences on MR imaging as well as ADC maps in 28 patients with PRES. The neuradiologic findings were correlated with levels of serum albumin, which is a main contributor to colloid osmotic pressure and vascular integrity. The presence of vasogenic edema was significantly associated with decreased serum albumin levels, which may be a particular risk factor for the development of PRES.

Alcohol challenge and sensitivity to change of the essential tremor rating assessment scale

The ability of the Essential Tremor (ET) Rating Assessment Scale (TETRAS) to detect changes in tremor severity is unknown.