Safer Way to Use Botox to Treat Challenging Dystonia Type?

Daniel M. Keller, PhD

October 05, 2021

When treating oromandibular dystonia (OMD) with botulinum toxin injection to the lateral pterygoid muscle (LPM), an intraoral approach is the safest way to avoid injury to the maxillary artery, new research suggests.

OMD causes an involuntary opening of the mouth, which can be disabling and disfiguring. Although injection of the LPM with botulinum toxin is the preferred treatment for OMD, a potential complication concerns the maxillary artery, which can run either lateral or medial to the LPM.

In a study of 200 patients, researchers documented significant variations between men and women in the anatomical location of the maxillary artery — and even found lateral vs medial differences on the left and right side in the same individual.

"The results showed that the maxillary artery runs lateral to the muscle in 67% of the Turkish patients," Rezzak Yilmaz, MD, Department of Neurology, University of Ankara Medical School, Ankara, Turkey, told meeting attendees.

Given this high rate, there is a high risk for injury "that may result in pain and hematoma" when using preauricular extraoral injections, the investigators note.

Instead, they recommend an intraoral injection approach to the LPM. "However, this critical anatomical variation is still unrecognized by most clinicians performing [botulinum toxin] injections," they write.

The findings were presented at the virtual International Congress of Parkinson's Disease and Movement Disorders (MDS) 2021.

Significant Gender Differences

The maxillary artery is the largest branch of the external carotid artery.

In the current study, the researchers used magnetic resonance angiography to assess the relevant anatomy in a cohort of 200 individuals (mean age, 56.4 years; 64% women) without a history of facial trauma or movement disorders.

Results showed that the maxillary artery ran lateral to the LPM in 67% of the study population.

"This result was also more frequent in females compared to males. Also, there was a considerable variability between the left and the right side in 20% of the participants," Yilmaz reported.

Additional findings are shown in the following table.

Table. Location of the maxillary artery in relation to the LPM 

Location Number (%)
On both left and right sides:


(total of both sides = 400 sides)

Lateral to LPM 268 (67%)
Medial to LPM 132 (33%)
On the right side:  
Lateral to LPM 140 (70%)
Medial to LPM 60 (30%)
On the left side:  
Lateral to LPM 128 (64%)
Medial to LPM 72 (36%)
Both sides lateral to LPM 114 (57%)
Both sides medial to LPM 46 (23%)
One side lateral, one side medial to LPM 40 (20%)


Statistically significant gender differences were found for the artery running lateral to the LPM on both sides (71.1% in women vs 58.5% in men; P = .007) and for the artery running lateral to the LPM on just the left side (69.8% in women vs 53.5% in men; P = .02).

In an email exchange with Medscape Medical News, Yilmaz said if medical personnel are not trained to perform an intraoral approach, "imaging to visualize the path of the maxillary artery before an extraoral/transcutaneous injection can be recommended."

"If the imaging reveals that the maxillary artery passes lateral to the muscle then the patient needs to be referred to another center for an intraoral injection," unless the clinician is trained for an intraoral approach, he added.

Useful Education

Commenting on the study for Medscape Medical News, Michele Tagliati, MD, director of the Movement Disorders Program at Cedars-Sinai Medical Center, Los Angeles, California, said the results were educational.

"I didn't know about all this variability. I was working under the assumption that the artery was medial," said Tagliati, who was not involved with the research.

Among his large practice of about 2000 patients, Tagliati estimated having five patients for whom he provides this type of injection — and has never encountered a problem with them.

"Maybe all my patients are medial, but now that I'm aware I’ll probably pay more attention," Tagliati said. He does not currently perform magnetic resonance angiography before injecting them, "although maybe I should," he said.

When asked if it is worth the time and expense to perform magnetic resonance angiography on every patient who comes in for LPM injections, Tagliati said although he has done the injections without problems in his current patients, he may "start obtaining imaging studies to make sure that we're not taking unnecessary risk" if the MA is lateral to the LPM in new patients.

If there is a risk, he'll then consider talking with colleagues in oral or facial surgery. Tagliati added that the number of patients he sees with OMD is rather small, so this extra step would not add a lot of additional imaging.

Overall, Tagliati noted that the study outcome was significant enough to want to use it for professional education. "I can definitely tell you that I'm going to bring it to the attention of my Fellows. I teach every year one or two Fellows to inject Botox," he said.

There was no funding for the study. Yilmaz and Tagliati have disclosed no relevant financial relationships.

International Congress of Parkinson's Disease and Movement Disorders (MDS) 2021. Abstract 109. Presented September 17-22, 2021.

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