14 Dystonia: Evaluation, Imaging and Medical Treatment

10.1055/b-0039-171733

14 Dystonia: Evaluation, Imaging and Medical Treatment

Travis J. W. Hassell and Fenna T. Phibbs

Abstract

Dystonia is a hyperkinetic movement disorder that involves intermittent or sustained muscle contractions that produce repetitive, patterned, and twisting postures with associated tremor. Accurate recognition of these features and understanding of appropriate pharmacologic therapy, chemodenervation strategies, and surgical interventions will lead to improved patient outcomes. This chapter will provide a concise set of clinical tools to accurately diagnose dystonia review current medical treatment strategies.

14.1 Introduction

Dystonia is a hyperkinetic movement disorder that involves intermittent or sometimes fixed muscle contractions that cause repetitive movements such as tremor or abnormal body postures. While dystonia is represented by a spectrum of clinical features, there are common presentations. Accurate classification begins by identifying the primary phenomenology of the abnormal movement. This chapter provides a concise set of tools to accurately identify and treat the key clinical features of dystonic syndromes.

14.2 Classification and Diagnosis of Dystonia

14.2.1 Clinical Features and Phenomenology

The recognition and diagnosis of dystonia can be difficult given the complex spectrum of clinical features, temporal patterns, wide range of affected ages, and overlap with other associated movements disorders such as essential tremor (ET) and Parkinson’s Disease (PD). A growing number of identified genes and genetic dystonic syndromes make it even more important to have a more systematic means to distinguish between dystonic patterns. A consensus statement was published in 2013 that revised the classification of dystonia, which is detailed in ▶ Table 14.1. Accurate classification relies on identification of two main characteristics: clinical features and etiology. ¹

**Table 14.1** Classification criteria for dystonia. Adapted from Camargos S, Cardoso, F. ²
Category	Classification	Subgroup
I: Clinical Features	Age at onset	Infancy (birth to 2 yrs.) Childhood (2 to 12 yrs.) Adolescence (13 to 20 yrs.) Early adulthood (21 to 40 yrs.) Late adulthood (40 and older)
	Body distribution	Focal (one body region – blepharospasm, orolingual, laryngeal, cervical, limb) Segmental (2 or more contiguous regions) Multifocal (2 or more non-contiguous) Hemidystonia (hemibody) Generalized (trunk plus 2 other sites)
	Temporal pattern	Course (static vs progressive) Variable (persistent, action-specific, diurnal, paroxysmal)
	Associated features	Isolated (with or without tremor) Combined (with other neuro or systemic disease)
II: Etiology	CNS pathology	Degenerative, structural, or neither
	Heritability	Inherited or Primary (genetic with various inheritance patterns)
	Idiopathic	Acquired or Secondary (metabolic, heavy metal (Wilson’s – copper), brain injury, drug induced, vascular, neoplastic, infection, psychogenic) Sporadic vs familial

Dystonic contractions are often initiated or worsened by specific tasks or voluntary movements producing abnormal and sometimes painful postures. Dystonic movements are most commonly seen as twisting about a longitudinal axis and often have a characteristic direction or pattern. ² . It is this patterned movement that helps to differentiate dystonia from other hyperkinetic movements. The muscles involved in the presenting posture are usually those affected, but dystonic contractions can occur into a muscle adjacent to the primary movement. This is termed overflow. Mirroring is a similar concept however, the dystonic movement is brought on by voluntary movement in the homologous, non-affected body part on the opposite side. ³ For example, dystonic wrist flexion can be brought out in the affected hand by writing with the unaffected hand. Several theories exist for dystonic movements, but a prevailing one is that there is impairment of surround inhibition at multiple levels within the central nervous system. This creates an imbalance of sensorimotor integration and an inappropriate output response that is manifested as abnormal co-contraction of specific muscle groups. ⁴ ^, ⁵ Electromyography (EMG) has shown that added sensory input changes muscle recruitment patterns. Patients often develop “sensory tricks” that can lessen these dystonic contractions. ⁴ ^, ⁵ ^, ⁶

When intermittent, dystonic muscle contractions often produce a tremor especially if there is an antagonist muscle attempting to provide balance. Differentiating dystonic tremor from other movement disorders with tremor as a predominant feature can be difficult. However, there are certain features of dystonic tremor that can be helpful. Dystonic tremor can be rhythmic or irregular with a jerky quality and is amplified when there is movement opposite to the direction intended by the dystonic muscle. This is seen in cervical dystonia. Dystonic tremor will generally lessen when the desired dystonic posture is reached. This is called a null point. ⁷ Isolated head tremor, or head tremor that precedes or is more severe than hand tremor is more likely to be a dystonic tremor than ET or PD. Dystonic head tremor often persists in the supine position whereas ET head tremor abates. ⁸

Dystonic tremor lessens when the desired posture or null point is reached.

Dystonic head tremor persists upon lying down whereas essential head tremor abates

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