Cervical Dystonia and Spasmodic Torticollis: Indications and Techniques

History of Dystonic Conditions

One of the earliest descriptions of dystonia was recorded by Gowers in 1888. Destarac in 1901 used the term “torticollis spasmodique” to describe the twisting neck movements observed in a 17-year-old girl. Dystonic conditions were identified as distinct from other hyperkinesias by Schwalbe in 1908; however, because of the bizarre nature of the movements, dystonias were originally considered a form of “hysterical neurosis.”

The term dystonia itself was first coined by Oppenheim in 1911, who was the first to correctly identify the organic nature of dystonia. However, focal dystonias, unlike the generalized condition, have been recognized for centuries. For example, the first recorded case of surgery for spasmodic torticollis dates back to 1641, when the German physician Minnius treated torticollis by sectioning the sternocleidomastoid muscle.

In 1944, the pioneering work of Herz revived the concept of dystonia being an organic disease, concluding from his frame-by-frame analysis of moving pictures showing that dystonic movements were slow, long-sustained, powerful, and nonpatterned contortions of axial and appendicular muscles. However, because of failures to identify associated brain lesions, arguments for an organic basis of the condition were not recognized until Marsden and colleagues studied cases of patients with hemidystonia. They discovered that lesions in the putamen, caudate nucleus, and posterior ventral thalamus were commonly present, contralateral to the hemidystonia. In the 1980s and 1990s, investigation into generalized dystonia, particularly among Jews of Ashkenazi descent, led to the discovery of the DYT1 gene mutation at the 9q34 locus. Since then, continued research has led to the awareness of a complex array of etiologic causes underlying dystonia, giving rise to an elaborate classification system for differentiating between dystonic conditions.

Epidemiology

Dystonic conditions are not rare. Epidemiologic surveys estimate that dystonia is the third most common movement disorder after Parkinson disease (PD) and essential tremor, and considerably more prevalent than a number of better-known neurologic conditions such as myotonic dystrophy, myasthenia gravis, and motor neuron disease. However, in contrast to many other conditions, there have been few published epidemiologic studies of dystonia. Differences in study design have further confused prevalence estimates, making it difficult to extrapolate data from certain studies to the general population. Combined estimates of prevalence around 330 per million have been made, encompassing all dystonias, with approximately one-third of all cases being due to cervical dystonia (CD). One of the most comprehensive examinations of prevalence estimates currently available was provided by the Epidemiological Study of Dystonia in Europe collaborative group, which estimated CD prevalence at 57 per million. However, true prevalence is unknown, with many authors suggesting that estimates in published reports are considerably lower than the actual prevalence due to significant numbers of undiagnosed cases within the community. This has implications with regard to the provision of patient care, particularly with respect to financing medical and surgical therapies for dystonic conditions.

Classification and Etiology

The term dystonia is employed to describe a syndrome characterized by sustained muscle contractions, often causing repetitive twisting movements or abnormal postures. These involuntary movements are caused by concurrent contractions of agonist and antagonist muscles and are often exacerbated during action but improve with relaxation, sleep, or sensory tricks (geste antagoniste) , such as touching the chin to improve CD. Some dystonic movements (e.g., writer’s and musician’s cramp) appear only with specific actions while others occur paroxysmally, in contrast to some that are present at all times. Dystonic conditions are heterogeneous and comprise an array of diseases that can be described both etiologically and descriptively.

Classification of Dystonic Conditions

An important aspect of the clinical evaluation of dystonia is the classification of the condition. This helps in formulating treatment strategies and deciding on the need for genetic counseling, and it may aid our understanding of the underlying pathophysiology of the illness. The latest system classifies the condition based on two axes: Axis I describes the clinical characteristics, while Axis II outlines etiology ( Box 106.1 ). The clinical description of dystonia based on Axis I facilitates the recognition of distinct dystonic syndromes without making assumptions about the underlying cause, which is dealt with separately by Axis II. The scheme is designed to allow the description of a dystonic condition to develop as clinical features evolve and more details emerge regarding etiology. Some of the main categories of these two axes are discussed in more detail below. Some common terms outside of this current system based on older classifications of dystonia are found in the scientific literature and are still in common use. These are mentioned briefly where relevant below.