Primary CD has two main clinical forms. The first is characterized by abnormal posture of the head and neck, limitation of head movements, and hypertrophy of overactive muscles, but no involuntary head movements. The abnormal posture can be purely rotational (torticollis), head tilt (laterocollis), head retroflexion (retrocollis), or anteflexion (antecollis), or a combination. Torticollis is the most common among single deviations, while torticollis plus laterocollis is the most common of the combined forms. The second form is characterized by the features of the first type plus involuntary head jerks (myoclonic dystonia). The head jerks are often exaggerated when the patient attempts to move the head toward the direction of movement limitation, and are sometimes seen exclusively at the end of the attempted rotation. In some patients, head movements are oscillatory (dystonic tremor) and difficult to differentiate from the cervical form of essential tremor. Remission occurs in 10–20% of patients, but is generally transient and usually does not last beyond one year.^5,6 Approximately 10% of patients disclose a history of CD in first-degree relatives, and 26–52% describe tremor or dystonia in family members.⁶ CD is distinct from other forms of late-onset dystonia because of pain, which is often described as ‘aching’ or ‘pulling’ and occurs in 70–75% of patients.^7,8 In one study the following distribution was reported: neck, 100%; shoulder, 73%; back, 46%; and arm, 15%. The maximum pain is usually felt in the muscles ipsilateral to the side of the chin deviation. Patients learn to perform sensory tricks (geste antagoniste) to improve head posture and decrease neck pain. The most common maneuver is touching the chin on the side of ipsilateral head rotation or tilt. However, pressing the head back against a high chair and holding the occipital region between interlocked fingers may also work. Sensory tricks usually lose some of their effectiveness with the passage of time.

Differential diagnosis of late-onset CD includes a number of secondary causes. Dystonic posture of the neck may arise from cervical spine disease or disorders of the cervico–cranial junction. CD can occur after head or neck injury, and dystonic posture of the neck may be seen during the course of a number of neurodegenerative disorders such as Parkinson’s disease, Parkinson plus syndromes, and Wilson’s disease. In the DYT⁷ form of genetic dystonia the pattern of dystonia is focal and often affects the cervical region. In some patients with DYT1 dystonia, CD may be the most prominent feature. In younger patients, the work-up should include brain magnetic resonance imaging (MRI), metabolic screening, and—in some patients—genetic testing. In older patients, when there is a suspicion of cervical spine disease one should obtain MRI of the cervical spine and the cervico–cranial junction.

Koukouni et al.¹⁰ reported clinical and genetic characteristics of 76 patients with CD with age at onset below 28 years (mean 21 years). The male-tofemale ratio was 1.24:1, and there was a family history of dystonia or tremor in 26%. Neck trauma or surgery was present in 17% of the patients. Onethird developed dystonia in the contiguous parts of the body. Another one-third experienced partial remission, but dystonia relapsed within five years. The DYT1 gene mutation was negative in all 15 patients who were tested for it. This young-onset CD seems to be distinct from the more common late-onset form of CD in terms of male predominance, higher incidence of family involvement, and more transient remissions.

Primary CD is probably a genetic disorder, but the precise genetic alteration needs to be elucidated. In one German kindred with DYT7 mutation, CD was the prominent dystonic feature.¹¹ In a recent study, the investigators showed that the presence of the D216H variant of the DYT1 gene in the absence of the DYT1 mutation increases the risk for developing CD even in patients without a family history of CD.¹²