I have had several botulinum toxin injections, but they do not appear to be of benefit. Why would that be?

There are several possibilities. One very rare reason why a person may not get a positive response is that they are genetically different; i.e., they have a resistance to the toxin so that it doesn't weaken their muscles. That is extremely rare. What can happen are two things after several injections have occurred:

1. The mechanism fatigues by which the toxin had been effective in the past – not antibody formation – just not as reactive; and
   
2. The antibodies have formed, and if they have formed, then the individual will lose the response to the A toxin and must wait for the clearance from the FDA for the B toxin, which we anticipate will be some time in the year 2000. It appears to be just as effective as A and as long of duration for benefit, but a higher frequency of induced dry mouth. There is no higher frequency of swallowing problems or neck weakness.

The other reason is that the individual receiving the injections may have gotten them in the wrong muscles. And to limit that possibility, EMG recordings are carried out to try to maximize the accuracy as to which muscles are most active and how can we cut those muscles down and give the patient the best possible outcome. Multiple channel EMG recordings before injection map out the areas of activation, and then the muscles are injected based on which are most active. Sometimes a conversion from the US made Botox™ to the British made Dysport™ results in improvement even though they are both botulinum toxin A (Botox™ is frozen, Dysport™ is refrigerated). Botulinum toxin B, by the way, is kept at room temperature whenever necessary, but it can be housed in a refrigerator, but it can't be frozen.

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