Botulinum toxin injection for bilateral recurrent laryngeal nerve paralysis
Reviewed by Christopher Burgess

All traditional surgical treatments for bilateral recurrent laryngeal nerve (RLN) paralysis are essentially a balance between maximising airway patency and ensuring adequate phonation / airway protection. This paper highlights the potential role of botulinum toxin (Botox) injection into the cricothyroid muscle bilaterally for the treatment of bilateral vocal fold paralysis to reduce obstructive airway symptoms. The patient population suitable for consideration of this intervention are those whose bilateral RLN paralysis results in an initial breathy dysphonia where the immobile vocal folds are in a relatively lateralised position. Over time, it has been noted that these patients’ dysphonia may improve but their airway may worsen due to unopposed action of the cricothyroid muscles. The clinical courses of three patients are reported who received Botox injections to their cricothyroid muscles to treat bilateral RLN paralysis following total thyroidectomies. Per side, 2.25-3.0 units were injected, and three to six separate injections had been performed a minimum of two months apart by the time of paper submission. Dyspnoea reportedly improved after each injection, with only minimal worsening of voice. Interestingly, two of the three patients did not experience recurrence of their dyspnoea eight months after their last injection, but whether this can be considered to represent long-term resolution is debatable. Clearly, a case series of three patients with largely subjective outcome measures is inadequate evidence for the benefit of Botox injections for bilateral RLN paralysis. Furthermore, the patient population who may benefit (stable airway, relatively lateralised vocal folds) will be a small subset of the total number of patients with bilateral RLN paralysis. Nevertheless, this intervention is certainly an interesting option for suitable patients with presumed bilateral RLN neuropraxia, given that the intervention is not permanent and does not preclude other therapeutic options in the longer term. 

Cricothyroid muscle botulinum toxin injection to improve airway for bilateral recurrent laryngeal nerve paralysis, a case series.
Benninger MS, Hanick A, Hicks DM.
JOURNAL OF VOICE
2016;30(1):96-99.