Presenters at several scientific sessions at the Combined Otolaryngology Spring Meeting (COSM) reported on their recent studies involving the use of botulinum toxin type A (Botox® [BTX]; Allergan, Inc., Irvine, CA) injections to treat adductor spasmodic dysphonia (ADSD) and chronic salivary aspiration.
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December 2007Botulinum toxin is produced by the bacterium Clostridium botulinum and achieves an irreversible neuromuscular blockade at presynaptic terminals, preventing the release of acetylcholine in response to action potentials.1 BTX cleaves to the SNARE protein, SNAP-25 (integral to the docking/release of acetylcholine vesicles at nerve endings), resulting in flaccid paralysis within a day or two that lasts for approximately three to four months.
During the past two decades, BTX therapy has been increasingly used to treat otolaryngological disorders of excessive or inappropriate muscle contraction before pursuing surgical options. These disorders include:
- Spasmodic dysphonia (adductor or abductor);
- Complex dystonias (oromandibular, laryngeal, cervical);
- Facial hyperkinesias (blepharospasms, hemifacial spasm);
- Vocal tics and stuttering;
- Cricopharyngeal achalasia;
- Various tremors and tics;
- Laryngeal granulomas;
- Posterior glottic synechiae;
- Gustatory sweating;
- Hypersalivation;
- Temporomandibular joint disorders; and
- Certain cosmetic applications.2,3,4
ADSD
Today, BTX injection is considered the gold standard treatment for ADSD, the most common clinical type of spasmodic dysphonia, in which there is increased activity of the vocal fold adductors, characterized by strained and strangled speech with breaks in pitch and phonation. The American Academy of Otolaryngology-Head and Neck Surgery has endorsed BTX injection for spasmodic dysphonia.
A patient with ADSD will feel the clinical effects of a laryngeal BTX injection into the thyroarytenoid (TA) muscle within 24 to 48 hours, but may experience breathiness and occasionally dysphagia for one to two weeks afterward. Symptoms will improve for a period of about two to five months, until new nerve terminals sprout and the muscle returns to its preinjection state and the cycle begins again. Because the effect is temporary, a patient is faced with the lifelong prospect of undergoing an injection procedure every three to four months. There is some concern that repeated injections may cause resistance or irreversible denervation to develop. The dose required for treatment varies due to the accuracy of injection, severity of ADSD, and sensitivity of the patient’s larynx to BTX.5
Dose Stability
Because there are few data regarding the long-term dose stability and consistency of BTX in the treatment of ADSD, researchers at the University of California, Irvine, Medical Center conducted a retrospective review of 13 subjects who had received a minimum of six injections (average = 11.5, range 6-19), to establish a baseline set of data to back the widely held belief that BTX dosing is stable in the treatment of ADSD.