Prolonged Effect of Botulinum Toxin Injection in the Treatment of Cricopharyngeal Dysphagia: Case Report and Literature Review

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Prolonged Eﬀect of Botulinum Toxin Injection in the Treatment of

Cricopharyngeal Dysphagia: Case Report and Literature Review

Ming-Jang Chiu, MD, PhD,

1

Yeun-Chung Chang, MD,

2

and Tzu-Yu Hsiao, MD, PhD

3

1

Department of Neurology,2Department of Medical Imaging,3Department of Otolaryngology, National Taiwan University Hospital, College of Medicine, National Taiwan University, Taipei, Taiwan

Abstract. Cricopharyngeus (CP) muscle spasm can

lead to severe dysphagia. Myotomy of the CP muscle

was the treatment of choice. Recently, botulinum

toxin type A (BtxA) has been used for CP spasm. It

usuallybrings improvement in deglutition but most

patients require reinjection in 3–5 months. We report

a 35-year-old man who had an arteriovenous

mal-formation hemorrhage in the brain stem resulting in

CP spasm and consequentlysevere dy

sphagia. He

received BtxA injection and deglutition and nutrition

remained good one year after treatment. A literature

review analyzing 28 patients and our patient showed

negative correlations between age and BtxA dose and

between age and duration. Eﬃcacywas positively

correlated with duration and BtxA dose was

posi-tivelycorrelated with pretreatment severity. In

con-clusion, physicians would use higher doses on

pa-tients with more severe cases but use lower doses on

older patients. Those who obtained better

post-treatment results would enjoylonger eﬀective

dura-tion. Thus, the eﬀective duration of the BtxA is

multifactorial.

Key words: Botulinum toxin type A —

Crico-pharyngeus muscle spasm — Dysphagia —

Deglu-tition — DegluDeglu-tition disorders.

Botulinum toxin type A (BtxA) is of signiﬁcant

therapeutic value in the management of a varietyof

hyperkinetic disorders such as blepharospasm,

tor-ticollis, writer’s cramp, orofacial dystonia, and

spasmodic dysphonia [1]. It is also eﬃcacious in the

treatment of facial nerve disorders such as synkinesis

or hemifacial spasm. It has also been applied in the

treatment of esophageal motilitydisorders such as

achalasia, hypertensive lower esophageal sphincter,

and upper esophageal sphincter spasm [2,3,4].

Dys-phagia due to hyperactivity of the upper esophageal

sphincter (UES), more speciﬁcallythe cricophary

n-geal (CP) muscle, can be seen in a varietyof

neu-rological

disorders

such

as

cerebral

vascular

accidents, amyotrophic lateral sclerosis, multiple

sclerosis, acoustic neuroma, and Parkinson’s disease.

It can also occur after surgical procedures for the

head and neck such as in resections for

oropha-ryngeal and supraglottic carcinoma as a

1 result of

iatrogenic injuryto the pharyngeal or recurrent

la-ryngeal nerves. Some causes of dysphagia are

idio-pathic [4–7]. Traditionally, surgical myotomy of the

CP muscle is the treatment of choice for

hyperac-tivityof the UES due to various causes [8,9].

However, CP myotomy is invasive and is not always

eﬀective [8]. BtxA was introduced in 1989 by

Schneider et al. [4] for patients with spasticity,

hypertonus, or delayed relaxation of the UES. The

intervention usuallybrings improvement in

degluti-tion but most patients require reinjecdegluti-tion in 3–5

months [5]. We report a patient with a brain stem

stroke who was left with CP sphincter spasm and

consequentlysevere dy

sphagia. He received BtxA

injection and deglutition and nutrition remained

good one year after injection. This is unusually long

for BtxA treatment in terms of its mode of action in

which neuromuscular transmission is

usuallyre-stored within 3–4 months. Thus, we did a literature

review to explore factors aﬀecting the eﬃcacyand

duration of BtxA treatment.

Correspondence to: Tzu-Yu Hsiao, M.D., Department of Otolar-yngology, National Taiwan University Hospital, 7, Chung-Shan S. Rd., Taipei, 100, Taiwan. Telephone: 886-2-23123456 ext. 5214; Fax: 886-2-23410905; E-mail: [email protected]

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Case Report

The patient was a 35-year-old man who suffered from severe dys-phagia with a disabilityrating scale (DRS) score of 4 [4] for about one and a half years after an episode of acute consciousness im-pairment from an arteriovenous malformation (AVM) hemorrhage in the left posterior pontomedulla (Fig. 1A,B). He received emer-gencysurgeryfor decompression and removal of blood clots. After the surgery, he gradually regained consciousness and motor func-tions. However, he was left with severe swallowing disturbance and required nasogastric tube feeding. Afterward, he had a significant bodyweight loss from a premorbid baseline of 73–74 kg to 66 kg (bodyheight = 175 cm). The neurological examination on ad-mission revealed leftward gaze palsy, left abducens palsy, and left peripheral-type facial palsy. Mild dysarthria with minimal hyp-ernasalitywas noted. Mild vocal cord palsyon the left side was also observed during laryngoscope examination. Hemihypoesthesia to pinprick and thermal stimulation over the right side of his body was also detected. No definite motor deficits, including weakness, muscle tone change, or abnormal tendon reflex, were detected. He could not drink even 20–30 ml of water without having to spit it out. Videofluoroscopic swallowing study(VFSS) showed almost no passage of barium into the esophagus. It showed severe dysphagia

with lower pharyngeal constrictor dysfunction or upper esophageal spasm. With written informed consent from the patient we per-formed an intrasphincteric BtxA injection.

About two weeks after the injection, the patient started oral feedings. He could drink small swallows of water and eat semisolid food such as pudding (DRS: 2). His swallowing con-tinued to improve and he could eat solid food the third week (DRS: 1). His bodyweight returned to 74 kg two months after the treatment (DRS: 0–1 ) and remained around 72 kg. At the one-year followup, his neurological condition was stable. He could eat and swallow almost normallyexcept for hard solid food at a rapid speed (DRS: 0–1). He had no complications such as acid regurgitation or belching from aerophagia. He received an-other VFSS about 10 months after the injection of BtxA (de-scribed below).

BtxA Injection Method

BtxA was obtained from Dysport (IPSEN, Berkshire, UK) as freeze-dried lyophilized preparation. For clinical use, BtxA ac-tivityis deﬁned in units, 1 unit representing the estimated median lethal dose for mice. Shortlybefore use, the toxin was dissolved with 2.5 ml of 0.9% sterile saline solution (without preservative), equivalent to 500 units. Under general anesthesia and direct lar-yngoscopic guidance, the bulk of the CP muscle was clearly identiﬁed. Botulinum toxin 0.6 ml, containing an equivalent dose of about 120 units of Dysport per site, was injected into the left and right lateral sides and the dorsomedial part of the muscle (Fig. 2).

VFSS

VFSS was performed with thin barium (5 ml), thick barium (5 ml), and paste barium (5 ml) in the lateral view and thin barium (5 ml) in the anterior–posterior view. The preinjection VFSS (about 3 months prior to the injection) showed almost no passage of barium into the esophagus with occasional pharyngeal–oral reﬂux, and laryngeal penetration (Fig. 2A). There was no aspiration. Poor contractilityof the lower pharyngeal segment with massive move-ment was also noted. VFSS showed a severe dysphagia with lower pharyngeal constrictor dysfunction or upper esophageal spasm. Fig. 1. A Preoperation cranial computed tomographyshows a hematoma in the left posterior pons. B The postoperation magnetic resonance imaging of the head reveals an arteriovenous malformation in the left pontomedulla.

Fig. 2. Under laryngoscopic view, the cricoid (C), esophageal lumen (E), and bulk of the cricopharyngeal muscle (CP) are clearly visible. The asterisks indicate the three injection sites.

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The first postinjection VFSS (about one month after the injection) revealed left-side predominant bilateral passage into the esophagus but no pharyngeal–oral reflux or pharyngeal–nasal reflux. The second postinjection VFSS (about 10 months after the injection) showed left predominant passage into the esophagus with mild oropharyngeal dysphagia (Fig. 2B).

We reviewed the literature, focusing on the efficacyof the BtxA injection and duration of effects. For this purpose, we searched MEDLINE using keywords cricopharyngeus, cricopha-ryngeal muscle, spasm, spasticity, hypertonus, dysphagia, deglu-tition disorder, swallowing disorder and BtxA; we found 7 reported series or cases reports [4,5,10–14]. We analyzed 28 of 30 cases from 5 reports [4,10–12,14] in which there was detailed in-formation on clinical diagnosis, severity, injection dose, efficacy, and duration of response to BtxA intervention. Together with our patient, 29 cases were subjected to further analysis (Table 1). The clinical severityof dysphagia was transformed into Schneider’s 5-point scale (0–4) DRS [4] for comparison. In Schneider’s DRS, score 0 indicates normal function, patient without complaints; score 1: no functional impairment, but subjective dysphagia when swallowing solid and/or liquid foods; score 2: mild functional impairment for solid and/or liquid food; score 3: marked disa-bilitywith moderate aspiration; and score 4: severe functional impairment with complete inabilityto swallow, considerable as-piration, and pneumonia. The efficacywas computed bysub-tracting the post-treatment DRS score from the pre-treatment score. Doses were transformed into Dysport equivalent units with

the ratio of Dysport:Botox = 3:1 [15, 16]. In cases with multiple treatments, the dose with the longest eﬀective duration was used for analysis.

Results

Descriptive statistics were reviewed in 6 women and

23 men with an average age of 62.8 ± 14.6 years. The

mean pretreatment DRS score was 3.48 ± 0.63 and

mean post-treatment DRS score 1.48 ± 1.30 with a

mean Dysport equivalent dose of 110.2 ± 79.1 units.

The mean eﬀective duration was 4.2 ± 2.9 months

with a mean eﬃcacyof 2.00 ± 1.34 change in DRS

score. For exploring eﬃcacyin patients with diﬀerent

clinical diagnoses, patients were further categorized

into three groups; Group 1, patients with

cerebro-vascular diseases, i.e., strokes (n = 10); Group 2,

patients with malignancies in the tongue base,

oro-pharynx, hypooro-pharynx, supraglottis, or larynx who

suﬀered peripheral nerve injuries after surgeryin the

upper neck (n = 13); Group 3 consisted of patients

Fig. 3. A Videoﬂuoroscopic swallowing study(VFSS) about 3 months prior to injection shows almost no passage of barium into the esophagus, pharyngeal– oral reﬂux, and mild laryngeal penetration. There is no aspiration. Poor contractilityof the lower pharyngeal segment with massive movement is noted. B VFSS, about 10 months after the injection shows left pre-dominant passage into esophagus with a mild oropharyngeal dysphagia and minimal laryngeal penetration.

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with other causes such as idiopathic dysphagia

(n = 6). A Kruskal–Wallis test showed no signiﬁcant

diﬀerences in the three groups for age, pretreatment

DRS score, post-treatment DRS score, eﬃcacy, dose

of BtxA applied, and eﬀective duration. However,

Spearman rho correlation showed that age was

neg-ativelycorrelated with the dose of BtxA (r =

)0.598,

p

< 0.0001) and with duration of eﬃcacy(r =

)0.463, p = 0.006). Eﬃcacywas positivelycorrelated

with duration of eﬃcacy(r = 0.448, p = 0.007). Dose

was not signiﬁcantlycorrelated with eﬃcacyor

du-ration but it was positivelycorrelated with the

pre-treatment DRS score (r = 0.370, p = 0.024). In other

words, although physicians used higher doses in more

severe cases, theyalso tended to use lower doses on

older patients, probablybecause the elderlyhad

de-creased muscle mass. The elderlyseemed to have

shorter eﬀective duration. Those who obtained better

post-treatment results enjoyed longer duration of

eﬀectiveness.

Discussion

UES spasm can have serious consequences leading to

complete inabilityto swallow, as in our case. BtxA

has been demonstrated to be therapeutic for CP

muscle spasm and hypertonicity. It can be used in

evaluating patients for permanent treatment such as

CP myotomy [5].

BtxA binds to the motor nerve terminal with

its heavychain [17], which is selective for cholinergic

nerve terminals. It is then internalized via endocytosis

[18], forming a vesicle inside the nerve terminal and

releasing its light chain into the cytoplasm [19]. It

blocks acetylcholine release by cleaving SNAP-25, a

cytoplasmic protein on the cell membrane, for release

of this transmitter [20]. Paralysis occurs as the

com-plete loss of miniature endplate potential starts.

Therefore, the therapeutic eﬀects of muscle weakness

are usuallyevident after a certain latencyranging

from a few days to 2–3 weeks. Chemical denervation

Table 1. Data from 31 patients with CP dysphagia

Case Age (yr) Sex Diagnosis Severity Prea _Dose _SeverityPosta _{Duration (months)}

S1 29 M Stroke, VI, X, XII 4 80/160 3 4.5

S2 52 M Supraglottic ca, partial laryngectomy 3 80 0 5

S3 47 F Oropharynx ca, lower jaw resection 3 80 0 5

S4 71 M Acoustic neuroma, IX, X 4 80 4 0

S5 55 M Stroke, tetraplegia 3 80 2 5

S6 45 M Brachyesophagus 2 80 2 0

S7 62 M Oropharynx ca, lower jaw resection 2 100 0 5

Ah1 48 M Stroke 4 240 0 3

Ah2 41 M HIV 4 180/300 0 4

Ah3 67 M Carotid EA, pharyngeal dysmotility 3 180/180 0 3

Ah4 65 M Stroke 4 180/180 4 2

Ah5 68 F Tongue base ca + R/T, S/T 4 120/180 4 14

At1 78 M Bulbar palsy+ apraxic gait 3 30 1 2.5

At2 85 M Progressive dysphagia + myotomy 3 30 2 2.5

At3 75 M Stroke; cerebellum, brainstem 4 45/60 2 1.5

At4 70 M Peripheral neuropathy3 60 3 0.5

At5 ? ? Medullar tumor, IX, X, XI, XII 4 ? ? ?

P1 52 M Hypopharynx ca + C/T, R/T 4 30–75 3–1 3–6

P2 72 M Stroke 3 45 1 3

P3 58 M Idiopathic 4 45 2 4

P4 76 M Idiopathic 3 45 2 3

P5 63 M Larynx ca + total laryngectomy 4 45 1 6

P6 69 M Larynx ca + total laryngectomy 4 45/90 2/1 4

P7 71 F Amyotrophic lateral sclerosis 4 75 3 4

P8 75 M Stroke, vocal palsy, unilateral 4 45/90 2/1 4

P9 58 M Larynx ca + total laryngectomy 4 60 1 6

P10 86 F Parkinson’s, Stroke 3 45 2 3

P11 80 F Idiopathic cervical dysphagia 4 45 0 4

P12 69 F Idiopathic cervical dysphagia 4 60 * *

R 68 F Oculopharyngeal muscular dystrophy 3 60 1 4

C 35 M Stroke, VI, VII, IX, X 4 360 0 12

?: not speciﬁed; *: lost followup; Dose: Dysport equivalent units (Dysport : Botox = 3:1).

a_{Severityfollowing S: Schneider [4]; Ah: Ahsan [11]; At: Atkinson [10]; P: Parameswaran [12]; R: Restivo [14]; C: Chiu; ca: carcinoma; C/T:} chemotherapy; R/T: radiotherapy; S/T: surgery; EA: endarterectomy.

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of the neuromuscular junction byBtxA results in an

expansion of the end-plate region and growth

stim-ulation of collateral axonal sprouts [21]. A nerve

sprout eventuallyestablishes a new neuromuscular

junction, and muscle activitygraduallyreturns. But

evidence also suggests the new nerve sprout retracts

and the original junction returns to functionality[22].

Theoretically, eﬀects are not permanent, lasting an

average of 3–4 months, which is the time needed for

re-establishing new neuromuscular junctions and

muscle activity. Our patient maintained good

deglu-tition for more than one year after BtxA injection. He

was the second youngest patient in our analysis and

responded verywell to the BtxA injection of 360

Dysport units. Although our patient received the

highest dose of BtxA among all reviewed cases, the

relation between the dose and duration of eﬃcacy

was not substantiated bystatistics. Some cases in our

reviewed series used doses of BtxA up to 240 (Case

Ah1) or 300 (Case Ah2) units but theysustained a

duration of about 3–4 months (Table 1). Thus, the

unusuallyprolonged duration of eﬀectiveness cannot

be fullyelucidated just through the denervation and

sprouting of the motor endplate. Other possible

mechanisms should be considered.

In our patient, the lesion involved the dorsal

pontomedulla aﬀecting the corticoreticular tract and

ﬁbers leading to the dorsal recticulospinal tract, which

is of crucial importance in the facilitation of the

in-hibitoryfunction from cortical neurons. The inﬂuence

of cortical motor areas over tone is

principallymedi-ated bya powerful mechanism in the bulbar reticular

formation. Loss of inhibitoryinﬂuence from the

cor-ticoreticular tract leaves the facilitating eﬀects of the

ventromedial reticular formation unopposed [23]. In

this situation, severe spasticitywith hy

pertonia is

greatest in the antigravityor postural-maintaining

muscles (composed of mainlyslow ﬁbers) such as the

closure maintaining CP muscle. Reduction of muscle

tone following treatment with BtxA results from eﬀects

of muscle denervation as well as inhibition of the

fus-iform system and muscle spindle [24]. Motor

innver-vation of the intrafusal muscle ﬁbers comes from

small-diameter motor neurons, called gamma motor neurons

to distinguish them from the large-diameter alpha

motor neurons. The gamma motor neurons provide a

mechanism for adjusting the sensitivityof the muscle

spindles. When a muscle is stretched, e.g., the CP

muscle is stretched during passage of a bolus coming

down from the oropharynx, the Ia aﬀerents in the

muscle increase their ﬁring rates leading to excitation

of the alpha motor neurons and contraction of the

muscle via the reﬂex arc. The activation of gamma

motor neurons causes increased intensityor lowered

threshold of the sensoryaﬀerents’ ﬁring from the

in-trafusal spindles. This coactivation of alpha and

gamma motor neurons serves as a feedback

mecha-nism from muscle spindles to reinforce the activation

of the alpha motor neurons. The swallowing peristaltic

waves come down from the oropharynx and the upper

pharynx to the CP muscle. The CP oriﬁce completes

the bolus passage through three steps. First is

relaxa-tion and opening of the oriﬁce. At this point, an

ab-normal hyperactive stretch reﬂex of the muscle would

impede the relaxation and thus prevent opening of the

oriﬁce. Second, after the opening, the CP muscle

con-tracts and closes the oriﬁce. Finally, it returns to the

resting state [25]. In the human CP muscle, the

hori-zontal inner layer contains more slow ﬁbers while the

outer oblique layer contains more fast ﬁbers [26].

In-terestingly, sprouting is generally slower in fast-twitch

muscles, which are more crucial in the stretch reﬂex,

than in slow-twitch muscles with predominantlytype I

fibers [27]. Thus, muscle-fiber-type specificity unique in

human CP muscle could be an additional factor in

prolonged eﬀectiveness.

In conclusion, the eﬀective duration of BtxA

injection in relieving CP spasm is multifactorial,

es-peciallyin cases with brain stem stroke. It diﬀers

from a simple denervation–reinnervation process as

in cases of hemifacial spasm. It also diﬀers from

hyperkinetic disorders such as spasmodic dysphonia

in that hypertonia results from rigidity but not

spasticity. It also diﬀers from spastic paresis, which

occurs in areas other than the CP muscle where

fiber-type specificity is not seen. A prolonged effect has

also been seen in upper [11] and lower esophagus

spasm [28]. Further studyon the mechanism is still

necessaryto clarifythis interesting and important

phenomenon.

References

1. Jankovic J, Brin MF: Therapeutic use of botulinum toxin. N Engl J Med 324:1186–1192, 1991

2. Pasricha PJ, Ravich WJ, Hendrix TR, Sostre S, Jones B, Kalloo AN: Intrasphincteric botulinum toxin for the treat-ment of achalasia. N Engl J Med 332:774–778, 1995 3. Jones MP: Botulinum toxin in hypertensive lower esophageal

sphincter. Am J Gastroenterol 91:1283–1284, 1996

4. Schneider J, Thumfart W, Potoschnig C, Eckel HE: Treat-ment of dysfunction of the cricopharyngeal muscle with botulinum A toxin: introduction of a new, noninvasive method. Ann Otol Rhinol Laryngol 103:31–35, 1994 5. Blitzer A, Brin MF: Use of botulinum toxin for diagnosis

and management of cricopharyngeal achalasia. Otolaryngol Head Neck Surg 116:328–329, 1997

6. Blitzer A: Cricopharyngeal muscle spasm and dysphagia. Op Tech Otolaryngol Head Neck Surg 8:191–192, 1997

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7. Born LJ, Harned RH, Rillers LF, Peiﬀer RF, QuigleyEM: Cricopharyngeal dysfunction in Parkinson’s disease: role in dysphagia and response to myotomy. Mov Disord 11:53–58, 1996

8. Mackenna JA, Dedo HH: Cricopharyngeal myotomy: indi-cations and technique. Ann Otol Rhinol Laryngol 101:216– 221, 1992

9. St. GuilyJ, Perie S, Willig T: Swallowing disorders in mus-cular disease: functional assessment and indication of crico-pharyngeal myotomy. Ear Nose Throat J 73:34–40, 1994 10. Atkinson SI, Rees J: Botulinum toxin for circopharyngeal

dysphagia: Case reports of CT guided injection. J Otolar-yngol 26:273–276, 1997

11. Ahsan SF, Meleca RJ, Dworkin JP: Botulinum toxin injec-tion of the cricopharyngeus muscle for the treatment of dysphagia. Otolaryngol Head Neck Surg 122:691–695, 2000 12. Parameswaran MS, Soliman AM: Endoscopic botulinum

toxin injection for cricopharyngeal dysphagia. Ann Otol Rhinol Laryngol 111:871–874, 2002

13. Restivo DA, Plameri A, Marchese–Ragona R: Botulinum toxin for cricopharyngeal dysfunction in Parkinson’s disease. N Engl J Med 346:1174–1175, 2002

14. Restivo DA, Marchese–Ragona R, Staﬃeri A, de Grandis D: Successful botulinum toxin treatment of dysphagia in oculopharyngeal muscular dystrophy. Gastroenterology 119:1416, 2000

15. Marion ME, SheehyM, Sangla S, Soulayrol S: Dose standardization of botulinum toxin. Lancet 59:102–103, 1995 16. Odergren T, Hjaltasaon H, Kaakkola S, Solders G, Hanko J, Fehling C, et al.: A double blind, randomized parallel group studyto investigate the dose equivalence of Dysport and Botox in the treatment of cervical dystonia. J Neurol Neu-rosurg Psychiatry 64:6–12, 1998

17. Brandypadhyay S, Clark AW, Desgupta BR, Sathyamoor-thyV: Role of the heavyand light chain of botulinum neu-rotoxin in neuromuscular paralysis. J Biol Chem 262:2660– 2663, 1987

18. Black JD, DollyJO: Interaction of125I-labeled botulinum neurotoxins with nerve terminals. II. Autoradiographic evi-dence for its uptake into motor nerves byacceptor-mediated endocytosis. J Cell Biol 103:535–544, 1986

19. Coﬃeld JA, Considine RV, Simpson LL: The site and mechanism of action of botulinum neurotoxin. In: Jankovic J, Hallet M (eds.): Therapy with Botulinum Toxin. New York: Marcel Dekker, 1994, pp 3–13

20. Blasi J, Chapman ER, Link E, et al.: Botulinum neurotoxin A selectivelycleaves the synaptic protein SNAP-25. Nature 365:160–163, 1993

21. Alderson K, Holds JB, Anderson RL. Botulinum-induced alteration of nerve–muscle interactions in the human orbi-cularis oculi following treatment for blepharospasm. Neu-rology 41:1800–1805, 1991

22. de Paiva A, Meunier FA, Molgo J, Aoki KR, DollyJO: Functional repair of motor endplates after botulinum neu-rotoxin type A poisoning: biphasic switch of synaptic activity between nerve sprouts and their parent terminals. Proc Natl Acad Sci USA 96:3200–3205, 1999

23. Brown P: Pathophysiology of spasticity. J Neurol Neurosurg Psychiatry 57:773–777, 1994

24. On AY, Kirazli Y, Kismali B, Aksit R: Mechanisms of ac-tion of phenol block and botulinus toxin type A in relieving spasticity: electrophysiologic investigation and follow-up. Am J Phys Med Rehabil 78:344–349, 1999

25. Duchen LW: Changes in the electron microscope structure of slow and fast skeletal muscle ﬁbres of the mouse after local injection of botulinum toxin. J Neurol Sci 14:61–71, 1971 26. Lund WS: The function of the cricopharyngeal sphincter

during swallowing. Acta Otolaryngol 59:497–510, 1964 27. Mu L, Sanders I: Muscle ﬁber-type distribution pattern in

the human cricopharyngeus muscle. Dysphagia 17:87–96, 2002

28. D’Onofrio V, Miletto P, Leandro G, Iaguinto G: Long-term follow-up of achalasia patients treated with botulinum toxin. Dig Liver Dis 34:105–110, 2002