The review question

We reviewed the evidence about the effect of botulinum toxin type A (BtA) in people with involuntary positioning of the head, or cervical dystonia. This is an update of a previous Cochrane Review and we assessed the effectiveness (reduction in severity, disability and pain) and safety of BtA versus placebo (a pretend medicine) in cervical dystonia.

Background

Cervical dystonia, also called spasmodic torticollis, is a disease that causes undesired, uncontrollable, often painful, abnormal placement of the head. It is a relatively uncommon condition (affecting 57 to 280 people per million) that can be very disabling and can affect a person’s quality of life negatively. In most cases the cause is unknown and no cure exists. Since cervical dystonia is normally a long-term disease it requires long-term treatment.

Botulinum toxin is a powerful, natural chemical that can cause severe paralysis (an inability to move in the part of the body where it is applied) in animals and humans. It can also be used to treat many conditions, in particular those with involuntary muscle contractions, such as cervical dystonia. Botulinum toxin is delivered by injections into the muscles that contract to produce most of the disease symptoms. There are different types of botulinum toxin, not all are available for treating health conditions. BtA is typically considered the first treatment option in cervical dystonia.

Study characteristics

We performed a rigorous search of the medical literature in October 2016 and found eight studies that compared treatment with BtA versus placebo. These studies included a total of 1010 participants, with on average a moderate disease impairment. The participants remained in the majority of studies for a short period of time – between 16 and 20 weeks after the treatment. The average age of people in the studies was 52.3 years, and they had had cervical dystonia for an average of 4.8 to 12.1 years before taking part in the trials. Most, 64%, of the people in the studies were women. Seven of the eight trials were funded by drug manufacturers with possible interests in the results of the studies.

Key results

The results show that a single treatment session improved cervical dystonia symptoms, including pain, and participant’s self-evaluations. However, the risk of having an unpleasant or undesirable event, particularly swallowing difficulties and tiredness, was also increased. Only three studies examined the impact of BtA on quality of life, suggesting some benefit from BtA.

Certainty in the evidence

The certainty in the evidence for overall and pain improvement, the risk of undesired events, self-evaluation, the risk of swallowing difficulties, and the risk of participants not tolerating treatment, is moderate.

Nevertheless, to be included in the studies, participants had to have a history of successful treatment with BtA. People with certain types of cervical dystonia, in particular the types that make the head turn mostly backward or forward, were not allowed to participate in the studies, and it is known that these types respond less to botulinum toxin treatment. Therefore, the conclusions from this review may not apply to all people with cervical dystonia.

We can draw no conclusions regarding long-term effects of BtA for this condition.