The Role of Electromyography in Guiding Botulinum Toxin Injections for Focal Dystonia and Spasticity

The accuracy of placing the needle used for botulinum toxin (BTX) injection in muscles was assessed in 45 patients receiving BTX treatment for focal dyastonia or spasticity. An electromyographer placed a needle capable of both injection and electromyogrpahy (EMG) recording in muscles selected for BTX injection. This was done while the EMG preamplifier was turned off to simulate BTX injection. This was done while the EMG preamplifier was turned off to simulate BTX injection without EMG guidance. After switching on the preamplifier, needle placement was assessed by analysis of motor unit potential (MUP) rise time. If the MUP rise time was less than 500 μ,s, the needle was considered correctly placed. IF MUPs were absent or distant, the needle was repositioned until MUP rise time was less than 500 μs. The distance the needle was repositioned was estimated in millimeters by direct observations. Forty-five patients had 381 separate BTX injections in 47 muslces. With initial needle placement, MUPs were abset in 2.8 perecent and distant of 3.0 mm (range 0.5 to 12 mm). In 2.4 percent of injections, only distant MUPs could be obtained despite repositioning. Judged by the percentage of initially correct needle placements and the distance of needle movement to achieve appropriate MUPs, the least accurate needle placements were in th eforearm flexors and small leg muscles. The most accurate needle placements were in large lower extremity and paraspinal muscles. The needle used for BTX injection was not optimally situated in the intended muscles, as judged by MUP rise time, in 29 percent of the injection sites initially selected without EMG guidance. This suggests that EMG needle guidance may improve the needle localization within the intended muscles compared with anatomic localization alone. This may contribute to a better therapeutic response and reduce complications of BTX treatment.