Botox Adverse Effects Every SLP Should Know

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Adverse effects after botulinum toxin (e.g. Botox, referred to hereafter as "BoNT") injections can have a significant impact on a patient's speech, swallowing, digestion, and respiration.

If you read my last post, you will know that botulism following BoNT injections (known as "iatrogenic botulism") can occur in mild, moderate, or severe forms. Keep in mind that there are no readily available/accurate objective tests for botulism, and that diagnosis can only come after a physician has ruled out other similar neurological impairments (stroke, GBS, meningitis, etc.).

SLPs should keep the following botulism symptoms in mind when they are assessing patients who present with idiopathic speech & swallowing disorders. Many of the symptoms listed below will resolve within 6-12 months post-BoNT injections for the majority of patients. It is still important that SLPs and injecting physicians are identifying these cases, however, because patients should be advised to stop BoNT injections if they are experiencing signs/symptoms of botulism from their injections. Re-injection can result in life-threatening botulism symptoms.

Dysphagia - Dysphagia has been reported in up to 25% of patients who receive BoNT injections in the neck muscles (cervical dystonia). Difficulty swallowing can occur in as many as 1-5% of patients receiving BoNT injections anywhere else in the body. If the neurotoxin spreads, either through adjacent muscle tissue or through the bloodstream, it can impact the following swallowing mechanisms:

• Salivation production: when BoNT enters the autonomic nervous system, or spreads to any of the salivary glands, is can significantly reduce saliva production, resulting in a dry mouth that can make bolus formation and transport difficult and strained.

• Tongue/jaw strength: if BoNT spreads into the facial or hypoglossal nerve, we may see slowed tongue movement, difficulty chewing, post-swallow residue, and delayed initiation of swallow

• Pharyngeal muscles: BoNT can cause delayed initiation of swallow, incomplete airway closure (resulting in aspiration- this is typically seen in moderate/severe botulism, but not mild botulism), reduced pharyngeal stripping motion, and pharyngeal residue

• Esophageal peristalsis: BoNT can weaken the muscles involved in esophageal clearance, and cause uncomfortable feelings of globus for hours.

Patients may report the following: "My food gets stuck", "I have to swallow everything hard", "My tongue feels slow", "my mouth is dry"

Dysarthria - The flaccid dysarthria seen in botulism occurs when BoNT spreads into one or more of the following cranial nerves: trigeminal (V), facial (VII), glossopharyngeal (IX), accessory (XI), or hypoglossal (XII). Patients will present with typical flaccid dysarthria characteristics, including slurred /labored articulation, hypernasality, slow rate of speech, breathy vocal quality, and possibly labored respiration.

Dysphonia - A hoarse voice (or complete loss of voice) can be a sign of BoNT spread to the vagus nerve (X). It is listed as a "common" side effect for patients who are treated with BoNT for cervical dystonia on Drugs.com.

Dyspnea - Shortness of breath or respiratory difficulties are a common sign of BoNT toxin spread, and per Botox's package insert occur in about 20% of patients who have BoNT-induced dysphagia after injections for cervical dystonia. BoNT can weaken the muscles of the diaphragm. In one study, iatrogenic botulism sufferers reported the following feelings: “not being able to take a deep breath”, “involuntary arrest of breathing for several seconds” and “need(ing) to constantly remind the self to breathe”. O2 saturations tend to remain normal in mild and moderate botulism. Severe botulism can require mechanical ventilation.

Incidence rates of the above symptoms in clinical trial patients, per BoNT product inserts (information obtained from drugs.com). Please note: the product inserts can be vague, and thus it can be difficult to obtain exact numbers on the incidence rates of these adverse effects:

Botox for Cervical Dystonia:

Dysphagia: 19%, with 20% of those cases experiencing dyspnea

Xerostomia: 2-10%

Dysarthria and/or dysphonia: 2-10%

Botox for Upper & Lower Limb Spasticity:

Dysphonia: 1-10%

Dyspnea: .1-1%

Botox for Hyperhidrosis (excessive sweating):

Dysphonia: >1%

Xerostomia: >1%

Dysphagia: >1%

Botox for migraines:

Dysphagia: .1-1%

Dyspnea: .1-1%

See https://www.drugs.com/sfx/botox-side-effects.html for more information.

SLPs: Remember to screen any patients who are presenting with these impairments and no obvious causal event/condition for history of BoNT injections.

References:

Botox product insert. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/103000s5302lbl.pdf

"Botox Side Effects". https://www.drugs.com/sfx/botox-side-effects.html 

Dysport product insert. https://www.accessdata.fda.gov/drugsatfda_docs/label/2023/125274s125lbl.pdf

Hristova, AH. Impaired neuronal communication syndrome (INCS) as novel neurological side effect to botulinum toxin type a therapy with 16 case reports. J Bacteriol Mycol. 2016; 3(4): 1035.