Dysphagia 8:2%34 (1993)

Dysphagia © Spnnger-VerlagNew YorkInc. I993

Swallowing, Speech, and Brainstem Auditory-Evoked Potentials in Spasmodic Torticollis Jennifer Homer, Ph.D., John E. Riski, Ph.D., Brace A. Weber, Ph.D., and Blaine S. Nashold, Jr., M.D. Department of Surgery, Duke University Medical Center, Durham, North Carolina, USA

Abstract. To explore the controversial "brainstem theory" of spasmodic torticollis, eight consecutively referred patients were examined. Three independent examinations were conducted on the same day: a videofluoroscopic barium swallowing examination, an instrumental speech examination, and a brainstem auditory-evoked potential (BAEP) analysis. Swallowing was normal in two patients; speech physiology, in five; and BAEPs, in all. Normal BAEPs refute the brainstem theory, while abnormalities of speech and swallowing temper this conclusion. Several alternative explanations are proposed. Key words: Barium swallow - - Instrumental speech analysis - - Brainstem auditory-evoked potentials - Spasmodic torticoIlis - - Deglutition - - Deglutition disorders.

data on both the pathophysiology and the clinical expressions of focal adult-onset dystonia (such as torticollis) remain inconclusive [10]. We examined patients with spasmodic torticollis in an attempt to replicate Drake's [18] result of abnormal brainstem function in this disorder and to explore the possible correspondence of BAEPs with speech and swallowing. We used three independent, objective analyses: videofluoroscopic evaluation of swallowing function, instrumental measurement of s p e e ~ function, and BAEPs. Patients with verified lesions of the brainstem often will manifest speech, swallowing, and/or BAEP abnormalities [19, 20]. We expected that, if the brainstem theory were true, abnormalities of swallowing, speech, and BAEPs would coincide.

Methods Although spasmodic torticollis in isolation or in association with other disorders has been studied extensively [1-13] the pathophysiology of this disorder is controversial. The well-recognized basal ganglia theory [3] is being challenged by a brainstem theory, according to Hedreen and colleagues [10]. Sources of evidence supporting the brainstem theory include experimental lesions [14], autopsy analyses [15], abnormal vestibular functioning [7, 8], and abnormal brainstem auditoryevoked potentials (BAEPs) [16-18]. Nevertheless, the

The authors have no commercial or proprietary interest in any product mentioned in this article. Address ofj))rint requests to: Jennifer Homer, Ph.D., Duke University Medical Center, Department of Surgery, Box 3887, Durham, NC 27710, USA

Subjects Eight individuals (two men, six women) with idiopathic spasmodic torticollis were examined on referral from a neurosurgeon (BSN) during a comprehensive preoperative evaluation for surgical candidacy. The speech and swallowing evaluations are a standard part of the care of torticollis patients at Duke Medical Center, while the BAEPs were performed free of charge. The eight patients were examined after consecutive referral to minimize any selection bias. Ages ranged from 32 to 62 years (mean 49.1). Duration of illness ranged from 1 to 11 years (mean 4.9). The direction of torticollis was specified by the chin position relative to the midline [7], with the head rotated or tilted in a sustained (tonic) or unsustained (spasmodic) manner. Leftward pulling torticollis was present in six; rightward, in two. No patient had a concomitant anterocollis or retrocollis. All patients showed "'isolated" torticollis [3], with no dystonia in body parts other than the neck, with the exception of subject 7 who also had pharyngeal dystonia (as verified by vide0fluoroscopic observations). No patient had an orthopedic abnormality, history of trauma to the head and neck, prior surgery for torticollis, or history of botulinum toxin injection.

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Procedures The three examinations were conducted the day before surgery in the Center for Speech and Hearing Disorders, Department of Surgery, Duke University Medical Center. The examiners (JH, JER, BAW) were blinded to the results of the respective evaluations until all data were interpreted. Videofluoroscopic Swallowing Evaluation. Oropharyngeal swallowing function was examined. The procedure, adapted from Logemann [21] requires an upright posture, lateral and anterior-posterior views of the oropharynx, three textures, and boluses graduated in size. Textures are: liquid (barium sulfate 45% weight/ water), "paste" (Esophotrast), and soft-solid (V4 piece of Loma Doone cookie, paste-coated). Liquid boluses are graduated as follows: Vzmeasured teaspoon, 1 measured teaspoon, 1 tablespoon "gulp," and multiple successive sips from a cup or straw. Each study was videotaped and the normalcy of oral-pharyngeal swallowing was observed, i.e., the oral-preparatory, reflex initiation, and pharyngeal phases. We used operational definitions of types of dysphagia as described by Riski et al. [22]. Mechanical dysphagia is the result of anatomical defects of the oropharynx [21] and is a diagnosis not applicable to the study population. Neurogenicdysphagia is attributable to an abnormality of reflexive or voluntary function, reflected in weakness or incoordination of the muscles of deglutition [21 ]. Operationatly, we considered any abnormality in reflex initiation or pharyngeal peristalsis to be a sign of neurogenic dysphagia. Posturaldysphagia [22] refers to an asymmetry of bolus transit through the pharynx as viewed in the anterior-posterior projection caused by changes in the relative positioning and/or dimensions of the laryngeal and pharyngeal structures [23]. Normally, with the head at midline during swallowing, large boluses fill the pharynx bilaterally and symmetrically during transit. However, asymmetry of bolus transit through the pharynx may be observed in normal swallowing under certain conditions [21 ]. First, forward tilting of the head typically wilt cause the pharynx to narrow, reduce the degree of laryngeal excursion required during swallowing, and facilitate epiglottic tilting [21 ]. Second, turning of the head to one side will obliterate the laryngeal-pharyngeal spaces on the side to which the head is turned, causing bolus transit to the opposite side. Third, tilting of the head will leave the spaces open, but will cause preferential transit through the spaces on the side to which the head is tilted due to the effect of gravity. In posturaI or movement disorders causing deviant head posture [23] such asymmetries of bolus transit are considered to be abnormal, i.e., postural dysphagia [22]. In torticollis patients, postural dysphagia in isolation rarely if ever causes swallowing to be dysfunctional, but may account for, or contribute to patients' subjective complaints [22]. A priori operational definitions of the degree of swallowing abnormality were established relative to current knowledge about normal [24, 25] and abnormal [21] swallowing: slight (asymmetry of pharyngeal transit only due to postural anomaly); mild (abnormal but adequate function in one of three phases); moderate (dysfunction in two or more phases); severe (dysfunction in all three phases, potentially including aspiration); see Homer et al. for detailed operational definitions and rating scales [26]. Instrumental Speech Evaluation. Objective measures of respiratory, respiratory-laryngeal, laryngeal, velopharyngeal, and articulatory function were obtained. The measure of respiratory function was forced vital capacity (FVC, using a Collins 8-1 Survey Spirometer). Respiratory-laryngeal measures included; phonation volume, phonation time, and calculated mean flow rate (MFR) for a sustained vowel sound (Collins 8-1 Survey Spirometer); oral pressure, oral air flow, and calculated laryngeal airway resistance for re-

J. Homer et al.: Swallowing, Speech, and Auditory Potentials peated syllables (palatal efficiency rating computed instantaneously interfaced with an IBM/XT PC [Perci-PC]). Laryngeal measures included: fundamental frequency, pitch range, and pitch perturbation (Visi-Pitch 6097). Measures of velopharyngeal function included: transnasal pressure drop, transnasal airflow, and calculated velopharyngeal gap during repeated words and sentences (Perci-PC). Oral diadochokinetic rates were used as measures of articulatory function and were measured from tape-recorded samples of repeated syllables (Visi-Pitch 6097). B r a i n s t e m A u d i t o r y - E v o k e d Potentials. BAEPs were recorded using the clinic's standard protocol for patients with suspected brainstem lesions. Unfiltered rarefaction and condensation click stimuli at 80 db HL were presented monaurally to each ear using insert earphones (Etymotic ER-3A). Stimulus rates of 13.3/s and 63.3/s were used. Two channel recordings (Fz-At and Fz-A2), obtained using gold-plated cup electrodes, were subjected to both analog and digital bandpass filtering (100 Hz to 3000 Hz). BAEPs were recorded on a clinical averager (Bio-logic Navigator) and each BAEP consisted of an average of 1000 individual responses. Two BAEPs were obtained for each stimulus condition. The resulting tracings were analyzed in terms of I/V amplitude ratio, absolute latencies, and interpeak latencies (IPLs) for component waves I, Ill, and V. BAEPs from the ear ipsilateral to the torticollis were compared with responses from the contralateral ear.

Results S w a l l o w i n g was n o r m a l in two patients; s p e e c h , in five patients; a n d B A E P s , in all s e v e n p a t i e n t s w h o g a v e scorable responses.

Videofluoroscopic Swallowing Evaluation (Table 1) At the time o f the e x a m i n a t i o n , all patients were tolerating r e g u l a r diets, a n d o n l y o n e p a t i e n t (no. 4) c o m p l a i n e d o f " o c c a s i o n a l " difficulty s w a l l o w i n g . O n v i d e o f l u o r o scopic o b s e r v a t i o n , six o f e i g h t p a t i e n t s s h o w e d a b n o r mal s w a l l o w i n g f u n c t i o n . N o p a t i e n t s h o w e d an oralp r e p a r a t o r y deficit. T w o (nos. 5 a n d 7) s h o w e d a m i l d l y d e l a y e d reflex, i.e., the reflex t r i g g e r e d after h e s i t a t i o n o f the b o l u s in the m i d p h a r y n x (at the epiglottis) r a t h e r t h a n at the p o s t e r i o r tongue. P h a r y n g e a l peristalsis was inferred f r o m the p r e s e n c e or a b s e n c e o f p h a r y n g e a l residue after the s w a l l o w . T w o patients (nos. 2 a n d 3) s h o w e d m i l d residue in the v a l l e c u l a r spaces ( m i d p h a r ynx) bilaterally; o n e o f w h o m (no. 3) also s h o w e d m i l d residue in the p y r i f o r m sinuses ( l o w e r p h a r y n x ) bilaterally. F o u r p a t i e n t s (nos. 1, 3, 7, 8) s h o w e d a s y m m e t r y o f b o l u s transit. T w o p a t i e n t s (nos. 1 a n d 7) w i t h l e f t w a r d p u l l i n g torticollis s h o w e d r i g h t w a r d p h a r y n g e a l transit, w h i l e a third p a t i e n t (no. 8) w i t h l e f t w a r d torticollis s h o w e d l e f t w a r d transit, a n d a f o u r t h (no. 3) w i t h rightw a r d torticollis s h o w e d l e f t w a r d transit. N o p a t i e n t aspirated. In s u m m a r y , six o f e i g h t p a t i e n t s s h o w e d a b n o r mal s w a l l o w i n g f u n c t i o n (two slight, four mild). F o u r

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J. Homer et al.: Swallowing, Speech, and Auditory Potentials Table 1. Swallowing characteristics of 8 patients with spasmodic torticollis examined by videofluoroscopy Case

Age (years)

Sex

Duration (years)

Head deviation

Subjective complaint

1 2 3 4 5 6 7 8

44 56 32 55 49 44 51 62

Male Male Female Female Female Female Female Female

1 2 10 5 11 2 5 3

Leftward Rightward Rightward Leftward Leftward Leftward Leftward Leftward

No No No Yes No No No No

Oral phase

Reflex initiation

Pharyngeal peristalsisa and symmetryb

Overall severityb

Type of dysphagiab

Normal Normal Normal Normal Normal Normal Normal Normal

Normal Normal Normal Normal Mild delay Normal Mild delay Normal

Rightward transit Mild bilateral residue Mild bilateral residue; leftward transit Normal Normal Normal Rightward transit Leftward transit

Slight Mild Mild Normal Mild Normal Mild Slight

Postural Neurogenic Postural and neurogenic Neurogenic Postural and neurogenic Postural

aResidue after the swallow indicates reduced pharyngeal peristalsis. bSee text for explanation.

patients shewed signs of postural dysphagia: two patient (nos. 1 and 8) showed postural dysphagia alone; two patients (nos. 3 and 7) showed signs of postural dysphagia with neurogenic dysphagia. Two patients (nos. 2 and 5) showed neurogenic signs only. The neurogenic signs observed were reduced pharyngeal peristalsis (nos. 2 and 3) and mildly delayed reflex initiation (nos. 5 and 7).

Instrumental Speech Evaluation (Table 2) Respiratory Function. Respiratory function, as determined by forced vital capacity (FVC), was normal in all eight patients. Six patients were above the expected FVC for their age, height, and gender; the two remaining patients performed at 92% (no. 6) and 84% (no. 4) of expected FVC [27]. Respiratory-laryngeal Function. Measures of respiratory-laryngeal function were also considered normal in all eight patients. Phonation volume averaged 2174 ml or 66% o f FVC. The phonation time for this task averaged 20.4 s. The mean flow rate (MFR) for this task averaged 111.6 ml/s and ranged from 65 ml/s to 173 ml/s. Oral pressure recorded during a repeated syllable task ranged from 4.8 cm Ha0 to 7.3 cm H20 and averaged 5.8 cm H20. The patient (no. 5) with the lowest pressure measure reported a habitually soft voice. Glottal airflow rates for this task averaged 163.5 ml/s and ranged from 98.6 ml/s to 296 ml/s. Calculated

Table 2. Summary of instrumental speech evaluations for eight patients with torticollis for respiratory, respiratory-laryngeal, laryngeal, velopharyngeal, and articulatory functions

Case

Respiratory; respiratorylaryngeal"

l

Normal

2 3 4

Normal Normal Normal

5 6 7

Normal Normal Normal

8

Normal

Laryngeal

Velopharyngeal Articulatory

Poor pitch controlb Normal Normal Vocal tremorc Normal Normal Poor pitch controlb Normal

Normal

Normal

Normal Normal Normal

Normal Normal Normal

Normal Normal Nasal air Escape Normal

Normal Normal Normal Normal

aRespiratory and respiratory-laryngeal functions are measured separately (see text), but results are collapsed here because all subjects performed normally on both sets of measures. bMildlyabdnormal in both patients 1 and 7. CMonosymptomaticessential voice tremor.

laryngeal airway resistance ranged from 18.6 cm H20 liters per second (LPS) to 56.1 cm H20 LPS and averaged 35.4 cm H20 LPS [28]. Laryngeal Function. Fundamental frequency, pitch perturbation, and pitch control were examined. All patients demonstrated nor-

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J. Homer et al.: Swallowing, Speech, and Auditory Potentials

mal fundamental frequency and pitch perturbation for their age and gender. Two patients (nos. 1 and 7) demonstrated difficulty with pitch control during the pitch range tasks. One female patient (no. 4) demonstrated poor control for sustaining a steady pitch for selected vowel sounds (e.g., "ee"), pitch breaks, and vocal tremor (5/s), the latter consistent with essential tremor [29]. Velopharyngeal Function. Seven patients demonstrated normal velopharyngeal function. One patient (no. 7) demonstrated a small amount of nasal air escape (19 ml/s) during articulatory transitions from oral to nasal sounds (e.g., "hamper") and during the production of high tongue carriage vowels (e.g., "people"). This patient also showed pharyngeal dystonia during the swallowing examination, but observation of velopharyngeal function during videofluoroscopy was precluded by her extreme head posture. Articulatory Function. All patients had normal articulation. All patients could repeat the single syllables "pa," "ta," or "ka" at 5.5 syllables per second or faster. No patient had speech distortions or irregularities.

Brainstem Auditory-Evoked Potentials (Table 3) Sufficiently clear BAEPs were recorded from seven of the eight patients. The one patient (no. 1) with poor quality BAEPs had a significant bilateral sensorineural hearing loss (thresholds at 4000 Hz were 65 dB and 70 dB) plus a high level of muscle artifact; his data were excluded from analysis. For the remaining seven patients, absolute latencies for waves I, III, and V fell well within clinical norms for both stimulus presentation rates, and there were no morphological or amplitude abTable 3. Brainstem auditory-evoked potential interwave intervals for

eight patients with spasmodic torticollis Ear ipsilateral to torticollis

Ear contratateral to torticollis

Case

l-III

III-V

I-V

l-lII

III-V

I-V

2 3 4 5 6 7 8 Mean

2.4 2.2 2.5 2.3 2.0 2.0 2.4 2.3

2.0 2.1 1.8 1.7 2.0 2.0 2.0 t.9

4.4 4.3 4.3 4.0 4.0 4.0 4.4 4.2

2.3 2.2 2.4 1.8 2.1 2.1 2.4 2.2

2.2 2.1 2.0 1.8 2.0 1.8 2.1 2.0

4.5 4.3 4.4 3.6 4.1 3.8 4.5 4.2

Note: Intervals are displayed for rarefaction polarity clicks presented at a rate of 13.3/s. No latency data are presented for case 1 because the level of muscle artifact made it impossible to identify waves with confidence.

normalities. Typical interwave latencies for BAEPs ipsilateral and contralateral to the torticollis are displayed in Table 3. Of particular note is the lack of interpeak asymmetry between stimulation ipsilateral and contralateral to torticollis. Only patient 5 showed asymmetry greater than 0.2 ms for any interval. For patient 5 this is due to unusually short intervals contralateral to the torticollis rather than abnormal prolongations for the ipsilateral ear. The asymmetry for this case was not present for condensation polarity clicks or at the fast (63.3/s) click rate. For the patients as a group, there are no significant differences in the I-III, III-V, and I - V intervals among any of the test conditions.

Discussion

Eight consecutively referred spasmodic torticollis patients underwent independent evaluations of swallowing, speech, and BAEPs. There was little agreement among the three independent evaluations. Signs of neurogenic dysphagia were observed in four patients. These neurogenic signs (delayed reflex initiation and pharyngeal residue) are reminiscent of those seen in poststroke patients [30]. Riski and colleagues [22] observed such neurogenic signs frequently in a series of 43 torticollis patients evaluated before surgery, as did Horner and colleagues [26] in a unique series of torticollis patients undergoing rhizotomy. Comella and colleagues [31] also observed defective peristalsis in 4 of 15 torticollis patients before botulinum toxin injections. Patterns of dysfunction observed in the present sample lead us to suggest that two patients showed signs of neurogenic dysphagia only; two patients, postural dysphagia only; and two patients, combined postural and neurogenic. To date, few studies have attempted to compare objective measures of speech system function with swallowing [32-34]. However several series of stroke patients have shown concurrent dysphagia and dysphonia [19, 30, 35, 36]. In the present series, three of eight patients had abnormal laryngeal function with dysphonia (nos. 1 and 7, poor pitch control; no. 4, essential voice tremor). Of these three patients, two showed concomitant dysphagia. Patient 1 showed signs of postural dysphagia, and patient 7 showed signs of combined postural and neurogenic dysphagia. Patient 4 complained of swallowing difficulty and had an essential voice tremor, but showed no swallowing abnormality on the videofluoroscopic examination. Further studies of speech and swallowing in patients with spasmodic torticollis are needed. BAEPs provided no evidence of brainstem dysfunction in any of the subjects. As a result, there was no clear relationship between BAEP measures and the pres-

J. Homer et al.: Swallowing, Speech, and Auditory Potentials

ence or absence of neurogenic dysphagia or dysphonia. This finding is in agreement with Narayan and colleagues [ 17] who detected no abnormalities in auditory, visual, or median and somatosensory evoked responses in patients with idiopathic torticollis. In contrast, Drake [18] reported longer I-III and I-V interpeak intervals for stimulation ipsilateral to torticollis when compared with controls and contralateral stimulation. The relatively small differences (approximately 0.3 ms) noted by Drake, however, were not present across the subjects in the present study. A reinspection of the BAEPs for stimulation ipsilateral to torticollis failed to show evidence of sufficient muscle artifact to suggest that true latency differences were undetected in the degraded evoked potentials. Both the Drake and the present study examined a small number of patients, so differences may be due to subject selection. Whatever the explanation, the present study does not support Drake's suggestion that ipsilateral brainstem dysfunction may be associated with torticollis in some patients. We offer a series of possible explanations for the lack of agreement among our swallowing, speech, and BAEP analyses. First, dysphagia in torticollis may indeed result from an anatomical defect within the brainstem. However, the BAEP, which reflects synchronous neural firings within the auditory pathways, may not be affected by the lesion. The BAEP is a purely sensory response, so a defect of brainstem motor pathways (potentially having concurrent effects on speech and/or swallowing) may not manifest itself in prolonged BAEP interwave intervals or abnormal response morphology. Further, the BAEP is thought to provide information about brainstem status between the cerebello-pontine angle and the level of the midbrain. As a result, specific lesions inferior to the cochlear nuclei or superior to the lateral lemniscus are not likely to be detected. Unfortunately, a satisfactory alternative electrophysiologic measure to the BAEP is not available. A second explanation for the lack of agreement among measures may be that the dysphagia may be purely "pos~ural," (as in patients 1 and 8), not neurogenic as we have suggested (patients 2, 3, 5, and 7). Though delayed reflex initiation and reduced pharyngeal peristalsis are consistent with neurogenic dysphagia, it is possible that states of chronic postural abnormality may alter timing and integrity of the pharyngeal swallowing reflex. If dysphagia in torticollis is purely "postural," the need for a "brainstem theory" to explain the dysphagia is unnecessary. We acknowledge that the subtle differences from normal in swallowing ability that we observed might be secondary to the abnormal posture of the head and neck incurred by the torticollis. As observed by Logemann [23], abnormalities of head and neck posture may cause changes in the size and shape of the oropha-

33

ryngeal cavity, as well as cause aberrations in the displacement of key structures (e.g., larynx, hyoid, and tongue) during swallowing [23]. Such displacements might have, in turn, secondary effects on the highly coordinated muscle actions during speech and swallowing. A third possible explanation for the discrepancies among our tests may be that the dysphagia may be purely "neurogenic" (as we suggest in patients 2, 3, 5, and 7), but may have a central origin other than the brainstem, e.g., in the basal ganglia [3, 37] or in one or more cortical regions [13]. Fourth, the dysphagia may be neurogenic but peripheral, not central, in origin. Altered innervation or function of extrinsic laryngeal musculature (elevators and depressors) might allow a lower motor neuron explanation for the observed dysphagia [26, 38]. Finally, the limited agreement between the swallowing and speech examinations is consistent with the idea that these motor functions have shared but not identical neural substrates [39, 40]. The limited agreement between our speech and swallowing data does not, therefore, necessarily preclude a central neurogenic explanation for the radiologically determined swallowing abnormalities. The data from this pilot study neither support nor definitely refute the brainstem argument. We suggest that the abnormalities we saw might be secondarily rather than primarily related to the torticollis of our subjects. The differences from normal that we observed might be due solely to abnormal posture, and not related to the underlying pathophysiology, located in the brainstem (or elsewhere) in the nervous system. To test the "theories" about the pathophysiology of speech and swallowing abnormalities in focal idiopathic torticollis patients, the sample of torticollis patients must be larger. Whereas we tested patients in order of consecutive referral, and each of three examiners were blinded to other tests, it might be worthwhile to preselect for BAEP and instrumental speech testing only those patients who show abnormalities on the videofluoroscopic swallowing evaluation. We suggest that further exploration of speech and swallowing function with objective measures of brainstem function such as BAEPs in torticollis is warranted. Replicable correlations among such data may eventually elucidate the pathophysiology of this challenging disorder or, at least, may help us in understanding its varied clinical expressions. References 1.

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