A Phase 2 Trial of Deep Brain Stimulation for Spasmodic Dysphonia

Spasmodic Dysphonia (SD) is a focal, action-specific movement disorder with prominent effects on speech (1, 2). Patients with SD lose their ability to speak normally due to involuntary contractions of their laryngeal muscles. As a result, SD tremendously affects an individual's quality of life by limiting their ability to communicate effectively.

The current standard of care for SD involves botulinum toxin (BTX) injections into the laryngeal muscles. BTX causes a weakness in the injected muscles thereby lessening the spasms (3). The primary neurological problem is not changed but weakening the muscles temporarily diminishes the symptoms. However, BTX therapy is associated with several limitations (3, 4). First, the clinical effect produced by BTX is temporary and repeated injections are required approximately every 3 months. Second, there is a delay in the onset of benefits provided by BTX injections; this delay results in a sinusoidal symptom curve where SD is optimally controlled for only a portion of each treatment cycle and patients' spasms return prior to the next injection cycle. Furthermore, the injections can be very painful and some patients develop antibodies to BTX (3, 4). Oral medications used in dystonia, such as anticholinergics, benzodiazepines, and baclofen, provide minimal relief and have numerous side effects at the doses required to influence a patient's voice. Thus, on basis of these limitations, we set out to explore new and innovative strategies to treat SD and provide patients with long-term benefit.

Deep Brain Stimulation (DBS) is a neurosurgical procedure that involves the implantation of electrodes to deliver electrical stimuli to specific brain regions. It is the gold-standard surgical treatment for other movement disorders such as Parkinson's disease and generalized dystonia. During a DBS procedure, an electrode is inserted very precisely into the brain and is linked to a pacemaker implanted under the skin of the chest or abdominal wall. When the pacemaker is switched on, a very small electric current passes into the brain, blocking the damaging signals that cause the condition.