Dystonia is a neurological syndrome characterised by involuntary, sustained, patterned and repetitive contractions of opposing muscles, leading to twisting and repetitive movements or abnormal postures of the body part involved.^1–4 Dystonic movements must be distinguished from other hyperkinetic involuntary movements such as chorea, myoclonus, tremor or tics. Dystonias can be classified according several factors: age at onset, body distribution and aetiology. Dystonias in which symptoms typically begin after 26 years of age are classified as adult-onset dystonias, whereas dystonias beginning earlier are generally called young-onset dystonias.^4,5 Focal dystonias involve a single body area, segmental dystonias affect contiguous body parts and generalised dystonias involve at least one leg, the trunk and another body part.^1–5 Multifocal dystonias (two or more noncontiguousbody parts) and hemidystonias (one side of the body) are less frequent body distributions.⁶ As for aetiology, primary dystonias are those in which dystonia (± tremor) is the only sign and symptom and no secondary cause or neurodegeneration is found. Conversely, secondary dystonias include a structural or a metabolic cause.^1,2,7 In turn, the primary dystonias can be either sporadic or inherited.^1,2,7

Cervical dystonia (CD), or spasmodic torticollis, affects the muscles of the neck and often the shoulders. It is the most common form of adult-onset focal dystonia, with an estimated prevalence of 5.7/100,000 in Europe.⁶ CD usually presents in the fifth decade of life, although it can affect individuals at any age.6 Although CD is classically described as being slightly more prevalent in females, both genders seem to be equally affected according to a European epidemiological study.⁸ Clinically, the predominant direction of the muscle twisting allows the identification of four core patterns of CD: rotation or torticollis (horizontal turning of the head), which is the most common; laterocollis (lateral flexion or tilt of the head); retrocollis (posterior extension of the head); and anterocollis (forward flexion of the head).⁹ In a series of 300 CD patients, Jankovic et al. identified torticollis in 82%, laterocollis in 42%, retrocollis in 29% and anterocollis in 25%.⁹ In a limited number of cases, the head may be shifted forward (forward shift) or off the midline (lateral shift).Nevertheless, Jankovic et al. found that the majority of patients (66%) had a combination of these patterns (complex CD).⁹ Head tremor (dystonic tremor) was found in 62% of patients, whereas hand tremor was present in 23%.³

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