Dysphagia Knowledge Hub — 吞嚥困難知識庫

Botulinum Toxin Injections for Dysphagia: Cricopharyngeal Dysfunction and Sialorrhoea Management

Botulinum toxin (BoNT) injection has become an established interventional treatment for two distinct dysphagia-related conditions: cricopharyngeal dysfunction (CPD), where abnormal upper oesophageal sphincter (UOS) activity obstructs the passage of food from the pharynx into the oesophagus; and sialorrhoea (drooling), where impaired intraoral saliva management in neurological conditions creates aspiration risk, discomfort, and social consequences. This article reviews the evidence base, patient selection, procedural considerations, and the clinical landscape for BoNT use in dysphagia in Hong Kong and internationally.

Botulinum Toxin: Mechanism of Action

Botulinum toxin type A (the most widely used formulation — commercial preparations include Botox, Dysport, and Xeomin) inhibits acetylcholine release at the neuromuscular junction, producing temporary, dose-dependent muscle relaxation. This effect is reversible: reinnervation occurs over 3–6 months as nerve terminals sprout, restoring function. The temporary nature of BoNT action is both a limitation (requiring repeat injections) and a clinical advantage (the effect can be allowed to wear off if the patient deteriorates or the treatment proves unhelpful).

Cricopharyngeal Dysfunction

Pathophysiology

The cricopharyngeus muscle constitutes the main component of the upper oesophageal sphincter (UOS). Normally, the UOS opens reflexively during swallowing — triggered by hyolaryngeal elevation and bolus pressure — and relaxes completely to permit bolus passage from the pharynx into the oesophagus. In CPD, the UOS fails to relax fully, opens incompletely, or is hypertonic at rest, resulting in a functional obstruction at the pharyngo-oesophageal junction.

CPD may be primary (idiopathic) or secondary to neurological conditions including brainstem stroke, Parkinson’s disease, motor neurone disease, and post-surgical cranial nerve injury. Radiologically, CPD may appear as a posterior pharyngeal bar or cricopharyngeal prominence on VFSS or barium swallow, though the correlation between radiological prominence and clinical impairment is imperfect.

Patients present with dysphagia predominantly for solids, food sticking at the level of the lower pharynx or upper chest, postprandial regurgitation, and in more severe cases, aspiration of retained pharyngeal residue.

Evidence for BoNT in CPD

Systematic reviews and meta-analyses support BoNT injection as an effective treatment for CPD. A pooled analysis across multiple case series and controlled trials demonstrates clinically meaningful improvement in dysphagia in approximately 70–80% of patients. Effects typically last 3–6 months, after which repeat injection is required.

BoNT injection for CPD is most effective in patients with demonstrated UOS hypertension or incomplete relaxation on manometry or VFSS, and least effective where dysphagia has a predominantly oral-phase or oropharyngeal aetiology. Patient selection through functional imaging and manometric assessment is therefore important for optimising response.

An important consideration: BoNT injection into the cricopharyngeus reduces UOS resistance, which improves bolus passage but also eliminates the protective barrier against oesophago-pharyngeal reflux. In patients with significant gastro-oesophageal reflux disease, this risk must be balanced against the dysphagia benefit.

Procedural Technique

BoNT injection into the cricopharyngeus can be performed under:

Doses range from 15 to 100 units of Botox equivalent, depending on the degree of hypertonia and the specific formulation used. All approaches carry a small risk of injection into adjacent structures, including the oesophageal mucosa, thyroid gland, or pharyngeal constrictors.

Alternative and Complementary Interventions

Endoscopic cricopharyngeal myotomy (dilatation or surgical section of the cricopharyngeus via endoscope, often using a laser or stapler) offers a more durable result than BoNT and is appropriate for patients who require multiple repeat injections or prefer a longer-lasting solution. Pneumatic or Savary dilation provides temporary relief in some cases. The choice between these modalities depends on surgical risk, patient preference, and local ENT expertise.

Sialorrhoea (Drooling) Management

Clinical Significance

Sialorrhoea is not excess saliva production but a failure to manage normal salivary volumes within the oral cavity — resulting from impaired lip seal, reduced swallow frequency, and incoordinated oral-motor function. It is a common and functionally significant problem in neurological conditions including Parkinson’s disease, motor neurone disease, cerebral palsy, traumatic brain injury, and post-stroke.

Beyond the social stigma and quality-of-life impact, sialorrhoea poses direct clinical risks: aspiration of pooled saliva (which is not sterile) contributes to aspiration pneumonia, particularly in patients already at elevated aspiration risk from dysphagia.

BoNT Injection for Sialorrhoea

BoNT injection into the salivary glands — specifically the parotid glands bilaterally, with or without submandibular gland injection — reduces salivary secretion by blocking parasympathetic cholinergic stimulation of glandular secretory cells. Unlike its effect on striated muscle, BoNT acts here on secretomotor nerve terminals supplying glandular acinar cells.

The evidence base is robust. Multiple randomised controlled trials and systematic reviews have demonstrated significant reductions in drooling severity and frequency following parotid ± submandibular BoNT injection across diagnostic groups including Parkinson’s disease, ALS/MND, and cerebral palsy. Effects typically last 3–5 months.

Standard dosing involves injection of 25–50 units of Botox equivalent per parotid gland, with 10–30 units per submandibular gland. Injections can be performed with palpation guidance in experienced hands or with ultrasound guidance to confirm gland localisation — the latter preferred for submandibular injections given proximity to the facial artery and marginal mandibular nerve.

Complications are generally mild and transient, including temporary dry mouth (xerostomia), difficulty chewing if masseter muscles are inadvertently affected, and, very rarely, temporary facial weakness from parotid injection.

Non-Pharmacological and Pharmacological Alternatives

Before or alongside BoNT, the SLT addresses postural management, swallowing frequency prompting, and lip seal exercises where motor capacity permits. Anticholinergic medications (glycopyrronium, hyoscine patches, oral scopolamine) provide an alternative but often produce systemic side effects (constipation, urinary retention, cognitive effects) that limit tolerability, particularly in elderly patients and those with dementia. BoNT injection is generally preferred when systemic anticholinergic side effects are a concern.

ENT and SLT Practice in Hong Kong

In Hong Kong, BoNT injections for cricopharyngeal dysfunction are typically performed by ENT surgeons within the Hospital Authority’s otorhinolaryngology departments, often under flexible laryngoscopy or direct laryngoscopy depending on the centre’s practice. SLT involvement in pre-procedure assessment and post-procedure swallowing rehabilitation is variable but recommended.

For sialorrhoea management, BoNT injection is performed by ENT surgeons and by neurologists at neurology centres managing Parkinson’s disease and MND — both groups have established BoNT practice. SLTs in HA dysphagia clinics and in private practice contribute to pre-injection assessment of drooling severity and post-injection monitoring.

Private ENT and neurology practices in Hong Kong also offer BoNT for both indications, with costs typically ranging from HKD 4,000–10,000 per treatment session depending on the preparation used and procedure complexity.

Summary

Botulinum toxin injection addresses two distinct mechanisms in dysphagia management. For cricopharyngeal dysfunction, BoNT reduces UOS hypertonia and improves bolus passage, with approximately 70–80% clinical response rate and effect duration of 3–6 months — supported by systematic review evidence. For sialorrhoea, parotid and submandibular BoNT injection reliably reduces salivary output and aspiration risk in neurological conditions, with robust RCT evidence across Parkinson’s, ALS/MND, and cerebral palsy populations. In Hong Kong, both applications are delivered through ENT and neurology departments within the Hospital Authority and in private practice, with SLT contributing to pre- and post-procedure assessment.