Distant effects of local injection of botulinum toxin

Abstract

We studied five patients who received local injections of botulinum toxin for dystonic disorders to determine if there had been any distant effects on neuromuscular transmission. No patient developed weakness or abnormalities on routine electrophysiologic testing. In all patients who received more than 245 U of toxin, SFEMG in the extensor digitorum communis muscle, a muscle distant to all those injected, was abnormal. Fiber density was increased in the two patients who received the largest cumulative dose. Jitter was maximally increased at slow firing rates, confirming its presynaptic basis. Our results reveal that there is an effect on neuromuscular transmission in muscles distant to those injected with botulinum toxin for dystonia.

Remote Effects of Chronic Botulinum Toxin Treatment: Electrophysiologic Results Do Not Indicate Subclinical Remodelling of Noninjected Muscles

“…In the already published papers, in 4 blepharospasm patients receiving periorbital BTA injections, FD remained normal in the upper limb, while transient neuromuscular blocking occurred [7]. In contrast, in 2 cervical dystonia patients, a direct relationship between BTA dose and FD was seen [8]. In 6 cervical dystonia patients, a single BTA dose caused a mild increase of biceps brachii FD within the normal range several weeks after injection.…”

“…FD quantitates the local concentration of muscle fibers within the motor unit, which can be used as a marker of reinnervation processes [11, 13]. In addition, several SFEMG studies documented subclinical remote effects of BTA injections [7, 8, 9, 15], but none reported on significant reinnervation of untreated muscles. FD of remote muscles seemed to depend on the time interval since the last injection, BTA dosage, distance of the injected muscle, and last but not least on examiner bias.…”

“…Using standard SFEMG software, the high-pass filter was set to 500 Hz, sweep speed to 0.5 ms and sensitivity to 100 µV per division. Only SF potentials whose amplitude exceeded 200 µV with rise times less than 300 µs were included in the measurements [8, 11]. FD was calculated as the mean number of SF potentials from at least 20 separate sites within the muscle.…”

“…From longitudinal morphological and functional studies it is well known that for the injected muscle, remodelling of motor units is an ongoing dynamic and probably dose-dependent process [4, 6]. In already published single-fiber electromyography (SFEMG) studies, transient subclinical effects on the neuromuscular function of remote muscles with increased jitter and blocking were observed [7, 8, 9]. Recently, a dose-dependent atrophy of type IIB fibers in the vastus lateralis muscle was reported after chronic BTA treatment of cervical dystonia.…”

Poison as cure: a clinical review of botulinum toxin as an invaluable drug

“…The most common adverse effect is the extension of the effect outside the intended area (12). This has been attributed to diffusion and difficulty in comparability of doses.…”