Botulinum toxin type A injection is well established as the standard of care for cervical dystonia, but there is little evidence to recommend optimal treatment intervals or dosing, according to a 2020 Cochrane review.

We spoke with neurologist Dr. Laxman Bahroo, director of the Botulinum Toxin Clinic at Georgetown University Hospital, to learn how he works around this lack of evidence to make the best clinical decisions for his patients.

This is the second part of a two-part conversation with Dr. Bahroo. You can read the first part here to learn how to target the right muscles and which guidance techniques are best for cervical dystonia Botox injection.

This interview has been lightly edited for clarity.

NI: How do you know how much Botulinum toxin to start with for a given patient with cervical dystonia?

Bahroo: There are standardized dosing ranges, and injectors are typically encouraged to start with dosing that’s on the lower end of that range, depending on the patient’s overall muscle bulk and size.

It’s critical to bring them back at about four weeks to see which muscles have responded well, which muscles will need additional dosing. It’s a stepwise process towards improving their posture and range of motion. To get to that optimal dosing, it can take anywhere from two to four visits.

Part 1: Targeting the Right Muscles in Cervical Dystonia

NI: How soon can you tell whether the dose you’ve chosen is right?

Bahroo: I typically tell people they might notice a response within about a week or so, but we bring individuals back at peak dose response about four to six weeks later to see and quantify the response (posture, range of motion). Evaluating the response helps decide dosing for next time.

NI: Which factors, including dosing, have the greatest influence on side effects?

Bahroo: Some postures involve muscles that are at higher risk. For example, a retrocollis posture makes it more likely that they will get weakness of the neck extensor muscles and have a head drop.

Next is the overall dosage or dosage in individual muscles. The higher the dosage, the more likelihood of developing potential weakness.

The third factor is dilution. If I’m injecting toxin that is more diluted, I am going to get more spread. Spread can be a good thing; it can allow me to get a better response into the muscle. Or it can spread too much into a nearby muscle and cause problems like respiratory difficulties or dysphagia.

NI: How often do you need to give a patient these injections?

Bahroo: No earlier than 12 weeks, or three months.

NI: How long can a patient go between injections?

Bahroo: In my opinion, established patients can make it to 12 weeks easily and probably 13 and a half weeks. You might have some super responders that come in every 14, 15, or 16 weeks.

We discovered this during the pandemic when a whole bunch of patients had to miss their appointments. People were anywhere from one month to several months off their injection cycles. Some of the people who were off for one month were surprised, saying, “I thought I’d be much worse, but I’m not.” Other patients said, “I now realize how much these injections do for me.”

We had patients on both sides of that divide.

Special thanks to Laxman Bahroo, DO, FAAN, director of Botulinum Toxin Clinic and Associate Professor of Neurology at MedStar Georgetown University Hospital. Bahroo is an Ambu consultant.