Effects of botulinum toxin on pathophysiology in spasmodic dysphonia

Contemporary management of spasmodic dysphonia

PURPOSE OF REVIEW

To review current concept in spasmodic dysphonia management.

RECENT FINDINGS

The standard of care for spasmodic dysphonia in 2004 remains botulinum toxin chemodenervation for symptomatic management. This is supported by a large body of literature attesting to its efficacy in many different hands, particularly for the adductor form of the disorder. New surgical approaches await the crucial test of time, in view of historical difficulties in achieving long-term benefit via recurrent nerve section, and currently, surgery is best reserved for the rare patient who does not benefit or cannot tolerate botulinum toxin injections. Despite efforts to refine both surgical and botulinum toxin treatment, symptom relief in abductor spasmodic dysphonia and dystonia with tremor remains suboptimal.

SUMMARY

Spasmodic dysphonia is a disorder of the central nervous system rather than the larynx, and as in other forms of dystonia, interventions at the end organ have not offered a definitive cure. The pathophysiology underlying dystonia is becoming better understood as a result of discoveries in genetically based forms of the disorder, and this approach is the most promising avenue to a long-term solution.

Central effects of botulinum toxin type A: Evidence and supposition

No convincing evidence exists that botulinum toxin type A (BT-A) injected intramuscularly at therapeutic doses in humans acts directly on central nervous system (CNS) structures. Nevertheless, several studies, using various approaches, strongly suggest that BT-A affects the functional organization of the CNS indirectly through peripheral mechanisms. By acting at alpha as well as gamma motor endings, BT-A could alter spindle afferent inflow directed to spinal motoneurons or to the various cortical areas, thereby altering spinal as well as cortical mechanisms. Muscle afferent input is tightly coupled to motor cortical output, so that the afferents from a stretched muscle go to cortical areas where they can excite neurons capable of contracting the same muscle. The BT-A-induced reduction in spindle signals could, therefore, alter the balance between afferent input and motor output, thereby changing cortical excitability.

Botulinum toxin injections for the treatment of spasmodic dysphonia

BACKGROUND

The use of botulinum toxin for the treatment of spasmodic dysphonia is currently the treatment of choice for management of this neurological voice disorder. Over the past 20 years, botulinum toxin has been used to treat both adductor and abductor forms of the disorder, with vocal improvement noted after treatment for both. A large number of studies have attempted to document the efficacy of botulinum toxin for improvement of vocal symptoms in individuals with spasmodic dysphonia.

OBJECTIVES

To determine the effectiveness of botulinum toxin for treating spasmodic dysphonia.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (1966 to July 2003), EMBASE (1974 to July 2003 ), CINAHL (through July 2003), Dissertation Abstracts International (1975 to July 2003) and PsycINFO (1975 to July 2003). The search engine FirstSearch was also used (July 2003). Reference lists for all the obtained studies and other review articles were examined for additional studies.

SELECTION CRITERIA

All studies in which the participants were randomly allocated prior to intervention and in which botulinum toxin was compared to either an alternative treatment, placebo or non-treated control group were included.

DATA COLLECTION AND ANALYSIS

Two reviewers independently evaluated all potential studies meeting the selection criteria noted above for inclusion. One study met the inclusion criteria and was included in the final analysis.

MAIN RESULTS

Only one study in the literature met the inclusion criteria. This was the only study identified which reported a treatment/no treatment comparison. It reported significant beneficial effects for fundamental frequency (Fo), Fo Range, spectrographic analysis, independent ratings of voice severity and patient ratings of voice improvement.

REVIEWERS' CONCLUSIONS

The evidence from randomized controlled trials does not allow firm conclusions to be drawn about the effectiveness of botulinum toxin for all types of spasmodic dysphonia, or for patients with different behavioral or clinical characteristics.

Botulinum toxin: application into acupuncture points for migraine

BACKGROUND

: Botulinum toxin has been employed in orthopedics, physiatrics, gastroenterology, gynecology, neurology, pediatrics, general surgery, plastic surgery, and several other specialties. We have applied this drug to treat hyperhidrosis and wrinkles in dermatology; it offers also a secondary benefit: relief for headaches.

OBJECTIVE

: We have performed studies based on acupuncture principles in order to develop new botulinum toxin application sites for the treatment of migraine. These additional sites are helpful when patients expect results for both their illness and their wrinkles; whereas some patients will show improvement with the classic treatment for wrinkles, additional sites may be required.

METHODS

: Ten patients suffering from migraine, as diagnosed through the criteria proposed by the Headache Classification Committee of the International Headache Society, were selected. We used easily recognizable acupuncture sites for the injection of botulinum toxin.

RESULTS

: There was significant improvement in patients with acupuncture site-guided botulinum toxin injection. It showed to be a safe and effective therapy for migraine.

CONCLUSION

: There are alternative sites besides those used for the treatment of expression lines, which bring forth an improvement of migraine.

Histology of nerves and muscles in adductor spasmodic dysphonia

To elucidate the etiology and pathophysiology of spasmodic dysphonia, we examined the adductor branch of the recurrent laryngeal nerve and the lateral cricoarytenoid muscle from 9 consecutive patients with this disorder who were previously treated with botulinum toxin. Histologic examination revealed average muscle fiber diameters ranging from 21 to 57 microm. Botulinum toxin treatment-related muscle atrophy was observed up to 5 months after injection. Endomysial fibrosis was present in all samples. Histochemical analysis in 8 patients revealed type 2 fiber predominance in 7 patients and fiber type grouping in 2. Type-specific muscle fiber size changes were not present. Nerve samples were examined in plastic sections. In 8 patients the nerves contained homogeneous, large-diameter myelinated nerve fibers and sparse small fibers. One patient had a relatively increased proportion of small myelinated nerve fibers. Overall, the nerve fiber diameter was slightly larger in patients than in controls. These findings may implicate the central nervous system in the pathophysiology of adductor spasmodic dysphonia.

Botox treatment in adductor spasmodic dysphonia: a meta-analysis

Over the years many studies have been conducted to document the treatment effects of Botulinum toxin type A in adductor spasmodic dysphonia. The results of these studies have led to the view that overall Botulinum toxin treatment is moderately effective. This study reviews efficacy research qualitatively and quantitatively to determine the extent to which this conclusion is fully supported by the data. Although the data indicate moderate overall improvement as a result of Botulinum toxin treatment, they also suggest significant variation across patients, measurements, and treatment conditions. This result, together with methodological limitations and lack of standardization in BT efficacy research, justifies caution when making inferences regarding BT treatment benefit in adductor spasmodic dysphonia.

Other noncosmetic uses of BOTOX

Botulinum toxin A has a wide variety of clinical applications, which are related by blockade of acetylcholine and often are related to abnormal muscle contractures. These applications include ocular disorders, disorders of the upper aerodigestive tract, dystonia and hemifacial spasm, cosmetic, gastrointestinal disorders, genitourinary disorders, management of pain, and use in autonomic nervous system disorders. Many of these diseases will be discussed with regard to their treatment with botulinum toxin compared to conventional treatments. Advantages and disadvantages of botulinum toxin use are delineated. General guidelines for adult and pediatric dosing will also be discussed.

The effect of botulinum toxin A on the vocal symptoms of spastic dysarthria: a case study

The vocal symptoms of spastic dysarthria and spasmodic dysphonia have many similar features. Botulinum toxin has been used effectively to treat spasmodic dysphonia. This study was designed to determine what vocal changes occur in an individual with spastic dysarthria following Botulinum toxin A injection into the thyroarytenoid muscles. Measures were obtained preinjection and three times postinjection. Acoustic and aerodynamic results were comparable to those reported for individuals with spasmodic dysphonia. The most marked change was increased DC airflow. Despite persistent breathiness, the participant reported great satisfaction with the result, particularly because of her more appropriate loudness. In addition, everyday listeners perceived significantly less listener burden and more relaxed and pleasant vocal quality postinjection.

Selective suppression of late laryngeal adductor responses by N-methyl-D-aspartate receptor blockade in the cat

Laryngeal adductor responses to afferent stimulation play a key role in airway protection. Although vital for protection during cough and swallow, these responses also must be centrally controlled to prevent airway obstruction by laryngospasm during prolonged stimulation. Our purpose was to determine the role of N-methyl-D-aspartate (NMDA) receptors in modulating early R1 responses (at 9 ms) and/or later more prolonged R2 responses (at 36 ms) during electrical stimulation of the laryngeal afferent fibers contained in the internal branch of the superior laryngeal nerve in the cat. The percent occurrence, amplitude, and conditioning of muscle responses to single superior laryngeal nerve (SLN) stimuli presented in pairs at interstimulus intervals of 250 ms were measured in three experiments: 1) animals that had ketamine as anesthetic premedication were compared with those who did not, when both were maintained under alpha-chloralose anesthesia. 2) The effects of administering ketamine in one group of animals were compared with increasing the depth of alpha-chloralose anesthesia without NMDA receptor blockade in another group of animals. 3) The effects of dextromethorphan (without anesthetic effects) were examined in another group of animals. In the first experiment, the occurrence of R2 responses were reduced from 95% in animals without ketamine premedication to 25% in animals with ketamine premedication (P = 0.015). No differences occurred in the occurrence, amplitude, latency, or conditioning effects on R1 responses between these groups. In the second experiment, the occurrence of R2 responses was reduced from 96 to 79% after an increase in the depth of anesthesia with alpha-chloralose in contrast with reductions in R2 occurrence from 98 to 19% following the administration of ketamine to induce NMDA receptor blockade along with increased anesthesia (P = 0.025). In the third experiment, R2 occurrence was reduced from 89 to 27% (P = 0.017) with administration of dextromethorphan while R1 response occurrence and amplitude did not change. In each of these experiments, NMDA receptor blockade did not have significant effects on cardiac or respiratory rates in any of the animals. The results demonstrate that NMDA receptors play an essential role in long latency R2 laryngeal responses to laryngeal afferent stimulation. On the other hand, early R1 laryngeal adductor responses are likely to involve non-NMDA receptor activation.

Acoustic measures of symptoms in abductor spasmodic dysphonia

Speech of patients with abductor spasmodic dysphonia (ABSD) was analyzed using acoustic analyses to determine: (1) which acoustic measures differed from controls and were independent factors representing patients' voice control difficulties, and (2) whether acoustic measures related to blinded perceptual counts of the symptom frequency in the same patients. Patients' voice onset time for voiceless consonants in speech were significantly longer than the controls (p = 0.015). A principle components analysis identified three factors that accounted for 95% of the variance: the first factor included sentence and word duration, frequency shifts, and aperiodic instances; the second was phonatory breaks; and the third was voice onset time. Significant relationships with perceptual counts of symptoms were found for the measures of acoustic disruptions in sentences and sentence duration. Finally, a multiple regression demonstrated that the acoustic measures related well with the perceptual counts (r2 = 0.84) with word duration most highly related and none of the other measures contributing once the effect of word duration was partialed out. The results indicate that some of the voice motor control deficits, namely aperiodicity, phonatory breaks, and frequency shifts, which occur in patients with ABSD, are similar to those previously found in adductor spasmodic dysphonia. Results also indicate that acoustic measures of intermittent disruptions in speech, voice onset time, and speech duration are closely related to the perception of symptom frequency in the disorder.

Assessment of posterior cricoarytenoid botulinum toxin injections in patients with abductor spasmodic dysphonia

In this study, we compared 2 techniques for injection of botulinum toxin type A (Botox) into the posterior cricoarytenoid (PCA) muscle for the treatment of abductor spasmodic dysphonia (ABSD). Fifteen patients with ABSD were enrolled in a prospective randomized crossover treatment trial comparing the 2 injection techniques. The PCA muscle was injected with 5 units on each side, with the injections staged 2 weeks apart, via either a percutaneous posterior-lateral approach or a transnasal fiberoptic approach. Eleven patients reported some benefit with the injections; however, the patient-perceived benefits were not related to changes in symptoms on blinded counts by speech pathologists. No significant reductions in the numbers of breathy breaks occurred with either technique, and no differences were found between techniques. Although patients perceived a benefit, blinded symptom counts did not substantiate these benefits. Thus, PCA muscle injections of Botox provided limited benefits to patients with ABSD, demonstrating the need for a more effective therapy for these patients.

Other noncosmetic uses of BOTOX

Botulinum toxin A has a wide variety of clinical applications, which are related by blockade of acetylcholine and often are related to abnormal muscle contractures. These applications include ocular disorders, disorders of the upper aerodigestive tract, dystonia and hemifacial spasm, cosmetic, gastrointestinal disorders, genitourinary disorders, management of pain, and use in autonomic nervous system disorders. Many of these diseases will be discussed with regard to their treatment with botulinum toxin compared to conventional treatments. Advantages and disadvantages of botulinum toxin use are delineated. General guidelines for adult and pediatric dosing will also be discussed.

Effects of adductor muscle stimulation on speech in abductor spasmodic dysphonia

OBJECTIVE

To determine whether adductor laryngeal muscle stimulation might be a beneficial treatment alternative for abductor spasmodic dysphonia (ABSD).

STUDY DESIGN

Baseline comparisons were made on measures of voiceless consonant and syllable duration between patients with ABSD and normal control subjects, and speech and voice production with and without muscle stimulation were compared within 10 patients with ABSD.

METHODS

Baseline group comparisons were conducted on measures of syllable and voiceless consonant duration between the patients and the control subjects. Neuromuscular stimulation was applied to the thyroarytenoid or lateral cricoarytenoid muscles in the patients during extended phonation, and measures were made of fundamental frequency and sound pressure level in the stimulated and nonstimulated conditions. Voiceless consonant duration was compared with and without adductor laryngeal muscle stimulation during syllable repetitions and sentences in the patients.

RESULTS

Before stimulation, the patients had increased syllable durations in comparison with control subjects (P = .003). Repeated within-patient comparisons with and without stimulation demonstrated significant (P < .008) reductions in voiceless consonant durations during syllable repetition. The more severely affected patients had the greatest reductions in voiceless consonant duration during sentence production.

CONCLUSIONS

Adductor muscle stimulation improved speech production in patients with ABSD, and the improvement was greatest in the most severely affected patients. Therefore adductor muscle stimulation has potential for benefiting patients with ABSD.