Drug Management in Cervical Dystonia
Drug Management in Cervical Dystonia
Cervical dystonia (CD) is a simultaneous and sustained contraction of both agonist and antagonist muscles of the neck. Based on head posture and positioning, cervical dystonia can be described as torticollis (neck rotation), anterocollis (head forward flexion or pulled forward), retrocollis (head posterior extension or pulled backward), or laterocollis (head tilt or lateral flexion). Combinations of the above postures are also common.
Clinical Manifestations
CD is the most common form of focal dystonia. Few epidemiological studies exist that estimate the incidence and prevalence of CD; separate studies of different geographical locations and times show the prevalence to be between nine and 30 per 100,000 individuals in the US.1–4
Currently, the prevalence of cervical dystonia in the US is estimated to be greater than 90,000. Other studies show that its prevalence differs among ethnic groups.5–7 Claypool et al., in 1995, reported an incidence of 1.2 per 100,000, while an incidence of 5.4 per 100,000 was published in a practice-based survey of dystonia in Munich.7Women are affected 1.3- to two-fold more often than men.CD can occur at any time of life, but most individuals experience their first symptoms in middle age. Chen et al. reviewed the clinical details of CD in 266 patients. In their study, the median age of onset was 41 years old, with a female to male ratio of 1.9 to 1. They found a familial history of dystonia in 12% of cases. Remission was achieved in 9.8% of patients.8
Pathophysiology
The pathophysiology of idiopathic CD is not well understood. Recent studies have explained the pathogenesis of CD at the peripheral and central nervous system (CNS) level. Although any muscle in the neck may be involved, the common muscles associated with abnormal head posture are well described.9,10 CD, like other focal dystonias, is a syndrome of abnormality in central motor processing. Head tremor and neck spasms are cardinal clinical features in patients with CD.8,11 The majority of affected patients complain of pain, which is not common in other types of focal dystonia other than writer’s cramp. Hand and arm tremor may be seen in patients with torticollis.11–13 In certain cases, head, arm, or trunk tremor can be the initial presenting symptom and sometimes the isolated manifestation of torticollis.14
Clinical Manifestation
Most patients with torticollis find a sensory trick a useful tool to control or eliminate their symptoms. A sensory trick has been called a ‘geste antagoniste’ and is a unique feature of dystonia.Typically, placing the hand on the chin, the side of the face or the back of the neck reduces muscle contraction in CD without applying mechanical pressure. In some patients, thinking about a geste antagoniste eliminates or diminishes their symptoms just the same as actually performing the sensory trick.15 Although the use of a geste antagoniste is reported in more than 50% of patients with CD11, its mechanism of action is still unknown.
Management
Medical Therapy
The efficacy of oral drug therapy is limited and many different medication trials show a low rate of success in controlling the symptoms of CD.16
Botulinum Toxin
Seven different serotypes of botulinum toxin have been identified. Their specific action is at cholinergic synapses to block presynaptic release of acetylcholine. By inhibiting the release of acetylcholine at the neuromuscular junction, they decrease inappropriate co-contraction of agonist and antagonist muscles in dystonia. Over the last 15 years, intramuscular injection of botulinum toxin has become the treatment of choice for patients with CD. Injection of the toxin into appropriate neck muscles relieves torticollis symptoms. Various controlled trials show 60–90% improvement following intramuscular toxin injection.17–23 Patients usually notice improvement of their symptoms starting five to 10 days after injection, with lasting benefit for three to four months. Peak benefit typically occurs within two to four weeks of injection. Two distinct serotypes of botulinum toxin are available for the treatment of dystonia in the US—types A and B.
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