Electromyographic assessment of spasmodic dysphonia patients prior to botulinum toxin injection

Electromyographic (EMG) evidence of inappropriate muscle activity (IMA) in the cricothyroid (CT) and vocalis (V) (thyroarytenoid) muscles was correlated with clinical voice measures in 32 patients with spasmodic dysphonia (SD). Subjective voice rating and quantified fluency and laryngeal diadochokinesis measures were obtained prior to botulinum toxin (Botox) injection into the V muscles. Pre-Botox EMG was performed using a monopolar needle electrode. Each muscle was sequentially examined at rest, during vocal click, scale, sustained "E" at different pitches, and repeated "E" voicings for brief periods. A three point EMG severity scale was used to grade the amount of IMA seen in each muscle. EMG evaluation showed no evidence of lower motor neuron involvement but did reveal IMA in 81.3% of the subjects. There were no significant correlations for the patients between different EMG-based IMA severity scales and the measures of voice quality and sound production. EMG did discriminate between predominantly adductor and abductor SD pattern types, but could not correctly differentiate a mixed SD group. Those patients with adductor SD displayed IMA in the V and CT muscles, while those with abductor SD displayed more IMA in the CT than the V muscles. Sequential EMG assessment of CT and V IMA in SD did not predict clinical severity or outcome following Botox injection into the V muscles.