Essential Tremor

Intramuscular Injections of Botulinum Toxin Type A

Although surgical intervention may be effective in patients with medication-resistant ET, it may not be desirable in all cases. For carefully selected ET patients, chemodenervation with localized injections of botulinum toxin (BTX) may be an appropriate alternative. Botulinum toxin type A as Botox® was originally introduced in the 1970s for the treatment of strabismus and blepharospasm associated with dystonia or facial nerve disorders. Chemodenervation with BTX is now increasingly being used as a therapeutic option for selected patients with other disorders characterized by severe muscle hyperactivity, including tremor, spasticity, and cervical dystonia.

Seven serologically distinct neuroparalytic toxins, designated as A through G, are produced by Clostridium botulinum bacteria. In the United States and worldwide, botulinum toxin type A is available as Botox®, which is produced by Allergan Inc., Irvine, CA, US. Another formulation of botulinum toxin type A as Dysport®, distributed by Ipsen Pharmaceuticals, United Kingdom, is available in numerous countries outside the US. Botulinum toxin type B is also available as Myobloc® in the US (Solstice Neurosciences) and Neurobloc® in Europe. Because these preparations are not equivalent unit for unit, caution must be used when converting units between the different formulations of botulinum toxin.

Botulinum toxin produces a chemical denervation of treated muscles through presynaptic inhibition of acetylcholine release at the neuromuscular junction. BTX binds to receptor sites on motor nerve terminals and inhibits neurotransmitter release without impeding acetylcholine synthesis or storage. Although the specific mechanism of action in the attenuation of tremor is unknown, local injections of botulinum toxin are known to affect muscle efferents and afferents and may alter the sensory feedback loop to the CNS.

Intramuscular injections of botulinum toxin type A as Botox have been used successfully to treat some patients with essential hand tremors, head tremors, and vocal tremors. Some experts believe that BTX-A is the treatment of choice in ET patients with head and vocal tremor.