Therapeutic challenges in dystonia

Tetrabenazine: Spotlight on Drug Review

BACKGROUND

Tetrabenazine (TBZ) is the only US Food and Drug Administration-approved drug for the treatment of chorea related to Huntington's disease and other hyperkinetic disorders. TBZ was first synthesized in 1950, and was then used for the treatment of psychosis. But later its potential in treating hyperkinetic disorders was proved by its ability to block vesicular monoamine transporters 2 and deplete monoamine stores. There is still lack of awareness about the therapeutic potential of this drug.

SUMMARY

TBZ had been approved only for the treatment of chorea, but several clinical studies have been conducted by different research groups and it was concluded that TBZ is effective in various other conditions such as tardive dyskinesia, dystonia, tics, and Tourette's syndrome, thus, highlighting the need for further clinical trials in these conditions.

KEY MESSAGE

The intention of this review is to sum up the information regarding chemistry, mechanism of action, pharmacokinetics, interactions, contraindications, adverse effects, and clinical efficacy of TBZ in diseases other than Huntington's chorea.

Prevalence, predictors, and perceived effectiveness of complementary, alternative and integrative medicine in adult-onset primary dystonia

BACKGROUND

Complementary and Alternative Medicine (CAM) use is on the rise in both the US and Europe, despite questions about its safety and effectiveness, and lack of national standards. We aimed to determine the prevalence and predictors of CAM and integrative medicine use (CAM-I) and perceived effectiveness compared to the standard treatment of botulinum toxin injections in patients with adult-onset primary dystonia.

METHODS

This was a retrospective questionnaire study of 389 dystonia patients examining the effects age, gender, education level and number of affected anatomical regions on botulinum toxin and CAM-I use and their perceived effectiveness.

RESULTS

53% (208) of patients reported CAM-I use, while 90% (349) used the standard treatment (botulinum toxin), and 48% used both. Education was the only significant predictor of CAM-I use - individuals with bachelor's degrees were more likely to try CAM-I whereas those with high school diplomas were less likely. The mean effectiveness rate for botulinum toxin injections (59%) significantly exceeded that for CAM-I (28%, p < 0.0001).

CONCLUSIONS

Our work highlights the need for scientifically sound studies to determine the safety, effectiveness and expense of CAM-I treatments for dystonia and other neurological disorders given that CAM-I use is steadily increasing, there is great variability in what is classified as CAM-I, and the effectiveness of some modalities may be significantly less than conventional medical treatments.

Update on pediatric dystonias: etiology, epidemiology, and management

Dystonia is a movement disorder characterized by sustained muscle contractions producing twisting, repetitive, and patterned movements or abnormal postures. Dystonia is among the most commonly observed movement disorders in clinical practice both in adults and children. It is classified on the basis of etiology, age at onset of symptoms, and distribution of affected body regions.

Etiology

The etiology of pediatric dystonia is quite heterogeneous. There are many different genetic syndromes and several causes of symptomatic syndromes. Dystonia can be secondary to virtually any pathological process that affects the motor system, and particularly the basal ganglia.

Classification

The etiological classification distinguishes primary dystonia with no identifiable exogenous cause or evidence of neurodegeneration and secondary syndromes.

Treatment

Treatment for most forms of dystonia is symptomatic and includes drugs (systemic or focal treatments, such as botulinum toxin) and surgical procedures. There are several medications including anticholinergic, dopamine-blocking and depleting agents, baclofen, and benzodiazepines. In patients with dopamine synthesis defects L-dopa treatment may be very useful. Botulinum toxin treatment may be helpful in controlling the most disabling symptoms of segmental or focal dystonia. Long-term electrical stimulation of the globus pallidum internum appears to be especially successful in children suffering from generalized dystonia.

Selective and sustained α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor activation in cerebellum induces dystonia in mice

Dystonia is a neurological disorder characterized by involuntary muscle contractions that cause twisting movements and abnormal postures. Functional imaging consistently reveals cerebellar overactivity in dystonic patients regardless of the type or etiology of the disorder. To explore mechanisms that might explain the basis for the cerebellar overactivity in dystonia, normal mice were challenged with intracerebellar application of a variety of agents that induce hyperexcitability. A nonspecific increase in cerebellar excitability, such as that produced by picrotoxin, was not associated with dystonia. Instead, glutamate receptor activation, specifically AMPA receptor activation, was necessary to evoke dystonia. AMPA receptor agonists induced dystonia, and AMPA receptor antagonists reduced the dystonia induced by glutamate receptor agonists. AMPA receptor antagonists also ameliorated the dystonia exhibited by the dystonic mouse mutant tottering, suggesting that AMPA receptors may play a role in some other genetic models of dystonia. Furthermore, AMPA receptor desensitization mediated the expression of dystonia. Preventing AMPA receptor desensitization with cyclothiazide or the nondesensitizing agonist kainic acid exacerbated the dystonic response. These results suggest the novel hypothesis that the cerebellar overactivity observed in neuroimaging studies of patients with dystonia may be an indirect reflection of abnormal glutamate signaling. In addition, these results imply that reducing AMPA receptor activation by blocking AMPA receptors and promoting AMPA receptor desensitization or negative allosteric modulators may prove to be beneficial for treating dystonia.