Use of BoNT-A in different types of focal dystonias has been well studied and has proven to be very effective. Botulinum toxin injection is the treatment of choice for cervical dystonia (spasmodic torticollis). [15, 16, 88] . A Cochrane review concluded that a single injection of BoNT-B was effective and safe for treating cervical dystonia. [89] This injection benefits the highest percentage of patients in the shortest time and has been proven effective in many double-blind, placebo-controlled trials.

BoNT has fewer side effects than do other pharmacologic treatments. The efficacy and safety of BoNT injections for the treatment of certain movement disorders, including blepharospasm, hemifacial spasm, oromandibular dystonia, cervical dystonia, focal limb dystonias, laryngeal dystonia, tics, and essential tremor is ongoing. [90]

In a double-blind, placebo-controlled trial by Greene and colleagues, 55 patients who previously had failed to find relief in 2 trials of medication received either BoNT or placebo in a double-blinded fashion and were tracked for 12 weeks. [91] Four weeks of open phase then followed when all patients received BoNT. By 6 weeks, 61% of patients showed improvement in head posture, and 39.5% reported reduction of pain. Both measures significantly improved (P< .05) compared to controls. During the open phase, patients who previously received placebo exhibited a similar response. Overall, 74% of patients improved by the end of the study.

A study by Brans and colleagues showed that in 64 patients with cervical dystonia, 84% reported long-term benefits in terms of impairment, disability, handicap, and quality of life (QOL). [92] Mezaki et all described their experience with a Japanese type A toxin for the treatment of cervical and axial dystonias. [93] Injections were given repeatedly at intervals of 28-30 days to carefully chosen muscles with increased activities, with a maximum dose per session of 300 units. The maximum improvements in subjective and objective ratings were obtained only after repeated injections.

Procedure

Treatment dosages of BoNT-A in the United States have been reported to range from 100-300 U per patient. In a double-blind, placebo-controlled study, Poewe and colleagues demonstrated that magnitude and duration of improvement were greatest after injections of 1000 U of Dysport, but the injections caused significantly more adverse effects. [94] The researchers recommended a lower starting dose of 500 U of Dysport (1 U of BoNT-A = 3 U of Dysport). One hundred U of toxin per mL of preservative-free normal saline are commonly used.

Injections are performed with a Teflon-coated, 24-gauge needle connected to an electromyographic (EMG) machine. Those muscles with highest clinical and EMG activity are injected. Usually, 2-4 separate muscles are injected in 1 session and, in larger muscles, 2-4 sites per muscle are injected.

No general consensus exists among users of BoNT regarding the need for EMG guidance while injecting the compound for cervical dystonia. EMG guidance, however, is helpful, particularly in obese patients whose neck muscles cannot adequately be palpated.

Identifying the specific muscles involved in cervical dystonia prior to the injection is important. Those most commonly injected are the sternocleidomastoid, trapezius, splenius capitis, and levator scapulae muscles. An EMG study of 100 patients found that 2 or 3 muscles commonly are abnormal. Eighty-nine percent of patients with rotating torticollis had involvement of the ipsilateral splenius capitis and contralateral sternocleidomastoid with or without the additional involvement of the contralateral splenius capitis. Patients with laterocollis had ipsilateral sternocleidomastoid, splenius capitis, and trapezius involvement, while retrocollis was produced by bilateral splenius capitis activity.

Beneficial effect from toxin injection usually is apparent in 7-10 days. Maximum response from the toxin is reached in approximately 4-6 weeks and lasts for an average of 12 weeks. Injections usually are repeated every 3-4 months.

Complications

Neck weakness, dysphagia, and local pain at the injection site are the most commonly reported side effects. Other adverse effects (eg, local hematoma, generalized fatigue, lethargy, dizziness, dry mouth, dysphonia, flulike syndrome, pain in neighboring muscles) also have been reported.

Most studies have reported side effects in 20-30% of patients per treatment cycle. The incidence of adverse effects varies based on the dosage used (ie, the higher the dose, the more frequent the adverse effects); however, Jankovic and Schwartz reported that incidence of complications was not related to the total dose of BoNT used. [95] Women and patients who received injections into the sternocleidomastoid muscles had significantly higher rates of complications.

Dysphagia has been the most prevalent significant complication and most probably is related to diffusion of the toxin into nearby pharyngeal muscles. In the study by Comella and colleagues, 33% of patients receiving their first dose of botulinum toxin experienced dysphagia. [96] This complication most commonly occurs with injections of the sternocleidomastoid and can be reduced significantly when the dose of toxin administered is 100 U or less.