Current concepts on the clinical features, aetiology and management of idiopathic cervical dystonia.

Idiopathic cervical dystonia (ICD) is the most common form of adult-onset focal dystonia. Previously, disagreement existed about whether ICD was a psychiatric illness, but the disorder is now viewed as a neurological illness and large clinical series have clarified the clinical features of the disease. At the time of diagnosis, extracervical dystonia is found in approximately 20% of patients, and there may be a concomitant head or hand tremor. Importantly, adult-onset ICD does not become generalized, although there may be segmental spread and pain may increase independently of the dystonia. While 10-20% of patients may experience remission, nearly all patients relapse within 5 years and are left with persistent disease. The aetiology of ICD is unknown, but there has been much progress in clarifying the genetic abnormality in families with inherited adult-onset cervical dystonia; linkage to chromosome 18p has been demonstrated in one family, and the DYT1 locus has been excluded in two other families. Painful trauma may be involved in the pathogenesis of ICD. Painful stimuli are received and processed by the basal ganglia, and the synaptic changes provoked by pain may lead to the abnormal physiology underlying dystonia. Consistent with this idea are experiments which demonstrate that altered sensory input leads to plasticity of the motor cortex, and those that explore the 'tonic vibration reflex' in patients with dystonia. Another theory suggests that a primary vestibular abnormality is responsible for ICD. Botulinum toxin is the most effective treatment for ICD. Roughly 75% of patients improve, and a response is generally seen within the first week. However, many questions remain regarding the optimal technique of administration. The development of neutralizing antibodies occurs in at least 5-10% of patients, and appears to be related both to dosage and to the interval between treatments. Side-effects are generally mild and result from the action of the toxin in the periphery. If the response to botulinum toxin is not adequate, anticholinergics, benzodiazepines, baclofen and other medications are used as adjunctive therapy. Surgical therapies are available for the treatment of ICD but are reserved for patients refractory to conservative measures.