Decoded Science: How does the Botox injection work to improve the tremors?
Dr. van der Walt: “Botox is injected into the muscles thought to be responsible for the main movements or components of the tremor. This often involves several injections into one or both arms. Most patients tolerate the injections very well and are keen to continue the treatment once they see the benefits they get from it.
The way in which Botox injections in muscles improve tremor, a condition that is caused by abnormal signals in the brain, is not completely understood. One stream of thought is that Botox (by blocking the release of an important nerve conduction agent acetylcholine) prevents stretching of the muscle and modifies the sensitivity or threshold of the nerves (called gamma motorneurons) in the belly of the muscle (muscle spindles) to fire. This change in the muscle-nerve interaction then affects the way the brain interprets the signals and decrease the severity of the tremor.”
Decoded Science: Could you explain the side effects that patients can experience as a result of this treatment?
Dr. van der Walt: “The main side effect of Botox was a temporary weakness affecting only the muscles that were injected. Mild weakness was defined as very mild weakness not interfering with the patient’s daily life, while moderate weakness was defined as weakness that was noticeable but that only interfered with daily activities some of the time. In this study, most of the weakness recorded was in the moderate category. As an example, one patient described having to use two hands rather than one when loading a full roasting tray into the oven while another had difficulty transferring in and out of her wheelchair for a few weeks. None of the patients developed severe weakness (that was defined by complete paralysis or inability to use the affected arm). The weakness resolved within a few weeks and limb function overall was better after the Botox despite the weakness.”