Botulinum toxin treatment of adductor spasmodic dysphonia: longitudinal functional outcomes

Laryngeal botulinum toxin (BoNT) injection is a well-established symptomatic treatment for adductor spasmodic dysphonia (AdSD). Injections may be followed by a period of muscle weakness characterized by breathiness, voice weakness, and dysphagia for liquids. A recent study described some detriment and limited functional improvement with "good voice" for only one-third of the period between successive injections. Our objective was to examine the longitudinal effect of BoNT treatment for AdSD upon functional outcomes and quality of life when using a patient-specific dosing regimen.

Prospective cohort study.

Patients presenting for BoNT treatment of AdSD were asked to complete evaluation of voice function after each injection using the percentage of normal function (PNF) scale (daily for two weeks, then weekly). Other parameters measured included voice handicap index (VHI), duration of effect, and complications.

A total of 133 patients treated continuously between January 2006 and January 2009 with an individuated regime (dose, pattern, and schedule) were included. Of 1,457 treatments, 50.9% experienced some breathiness. Mean VHI improvement was 9.6%. Mean PNF improvement was 30.3%. There was correlation between the two scales. Dysphagia to liquids was reported after 14.2% of treatments. We describe two distinct types of functional outcome curve. A total of 28.5% of treatments were followed by initial functional decline. Mean time below baseline function was 5.7%. Mean proportion of time in plateau phase was 42.5%.

It is important to consider longitudinal functional outcomes in BoNT treatment of AdSD. An individuated dosing regimen helps minimize side effects and maximize functional and quality-of-life outcomes.