According to a study in the January issue of Anesthesia & Analgesia, the official journal of the International Anesthesia Research Society (IARS), Botox (Botulinum neurotoxin type A) has previously unsuspected ‘systemic’ effects on muscles other than the ones it’s injected into.
Researchers have demonstrated in experiments with rats that the lasting effect of Botox injections also occurs in muscles distant from the injection site, and that it appears to cause a unique effect on the muscle responses to a commonly used muscle relaxant, which could impact the monitoring of a patient during surgery or mechanical ventilation.
Research leader Dr. Christiane G. Frick of Massachusetts General Hospital in Boston and her team examined the immediate, delayed, local and distant effects of Botox injections by conducting various experiments.
Botox, which is most famous for its application in cosmetic procedures, is also used to treat neuromuscular disorders. It works by interrupting the signals between nerves and muscle tissue and causes temporary paralysis of the injected muscles. This could be facial muscles that have caused wrinkles or spastic muscles in patients with cerebral palsy.
In the study, Frick injected rats with a single injection of Botox into the tibialis muscle of the hind leg. As expected, the researchers noted that the injected muscle was completely paralyzed after four days, however, they discovered that the tibialis muscle in the other hind leg also displayed lower twitch responses to electric stimulation even though no substantial effect on muscle function was observed.
At sixteen days, the researchers observed that the Botox-injected muscle still showed decreased function, twitch responses, and muscle tension and that the twitch responses and muscle tension in the non-injected tibialis muscle also remained substantially lower, although to a lesser extent. The finding indicates that Botox also causes long-lasting changes in ‘distant’ muscles in addition to the temporary paralysis in the injected muscles.
The findings also revealed changes in responses to the muscle relaxant drug atracurium, which could result in significant clinical implications, given that atracurium is commonly administered to patients undergoing surgery or mechanical ventilation in order to relax the muscles. The researchers observed that in particular those muscles injected with Botox showed a uniquely higher sensitivity to atracurium. These effects lasted longer than 16 days.
Clinicians generally monitor muscle twitch responses to evaluate atracurium’s effectiveness on relaxing the muscles. According to the new findings, recent Botox injections, whether administered for cosmetic or neuromuscular disorders, could potentially affect patient monitoring during surgery. This has been demonstrated in a recently reported case, in which an anesthesiologist was using twitch responses in the forehead to monitor the degree of atracurium block elsewhere in the body.
Dr. Steven L. Shafer of Columbia University and Editor-in-Chief of Anesthesia & Analgesia explained:
“Although we knew that Botox has lasting effects on muscle function, this study suggests that these muscle effects may be seen quite distant from the injected muscle. If you’re a patient undergoing surgery who has had a recent Botox injection, it might be a good idea to mention it to your anesthesiologist.”
Written by Petra Rattue