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Chapter 39 - Treatment of Focal Hand Dystonia
- Edited by Daniel Truong, University of California, Riverside, Dirk Dressler, Hannover Medical School, Mark Hallett, National Institutes of Health (NIH), Christopher Zachary, University of California, Irvine, Mayank Pathak, Truong Neuroscience Institute
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- Book:
- Manual of Botulinum Toxin Therapy
- Published online:
- 02 November 2023
- Print publication:
- 23 November 2023, pp 332-347
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Summary
Focal hand dystonia (FHD) is characterized by dystonic hand contractions that are often aggravated by purposeful actions and may be specific to a particular task. The term “occupational dystonia” is used when dystonia affecting performance of the job arises in individuals with a particular occupation, usually an occupation requiring repetitive and excessive fine motor activity.
One task-specific FHD, writer’s cramp, causes disabling spasms of the hands when attempting to write, and is particularly likely in people whose profession involves excessive writing. Musician’s dystonia (cramp) is applied to a focal dystonia localized to hand muscles controlling fine movements of the digits or the embouchure muscles involved in playing instruments.
Injection of botulinum neurotoxin (BoNT) is effective in writer’s cramp and other occupational dystonias. This chapter discusses the different common patterns of dystonic movement of the hand and arm, identifies the particular muscles active in each dystonia pattern to aid in target selectio, and illustrates the muscular anatomy and injection approach using anatomical diagrams. Guidance of injections with EMG is discussed. Dosing recommendations for three different BoNT formulations are tabulated.
9 - Treatment of focal hand dystonia
- Edited by Daniel Truong, Dirk Dressler, Mark Hallett
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- Book:
- Manual of Botulinum Toxin Therapy
- Published online:
- 28 July 2009
- Print publication:
- 12 February 2009, pp 61-76
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- Chapter
- Export citation
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Summary
Definition
Dystonic contractions are often aggravated by purposeful actions and may be specific to a particular task. A patient may have dystonia when using the hand for writing but not for other tasks such as eating or typing. Occupational dystonias are those that occur in individuals with a particular occupation requiring repetitive and excessive fine motor activity. Most of these dystonias are task specific and fall under the rubric of primary focal dystonias. The occupations especially prone to have focal task-specific dystonia are listed inTable 9.1.
In this chapter we discuss in detail writer's cramp and musician's cramp, the two most common occupational dystonias, followed by a brief mention of other focal occupational dystonias.
Pathogenesis
Although the exact cause of these focal dystonias is not yet elucidated, it seems that an interaction of proprioceptive, behavioral, genetic, gestural, environmental, and psychological factors plays a role. Excessive activation of antagonists, overflow into synergists, and prolongation of muscle activation are thought to reflect deficiency of premotor cortical network inhibition (Hallett, 2000, 2006a, b). Decreased levels of the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) are present in the contralateral sensorimotor cortex and lentiform nucleus in patients with writer's cramp (Levy & Hallett, 2002). Functional magnetic resonance imaging shows impaired activation of the primary sensorimotor and supplementary motor cortex during voluntary muscle relaxation and contraction (Oga et al., 2002). A genetic factor in the development of hand dystonia is possible, as up to 20% of patients with writer's cramp have family members with dystonia.