Dystonia, defined as a movement disorder characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both, results in patterned, twisted, and sometimes tremulous movements. When dystonia is the sole manifestation, it is known as primary dystonia. Primary dystonia is an uncommon disorder and includes genetic forms of dystonia as well as idiopathic dystonia. Dystonia can involve one body part, when it is called focal; more than one contiguous body part, when it is known as segmental; or involving the trunk and more than two body parts, when it is called generalized. This chapter reviews primary dystonia: the epidemiology, the current theories of pathophysiology, the clinical description, and available treatments of genetic as well as the various forms of focal dystonia, including blepharospasm, oromandibular dystonia, laryngeal dystonia, cervical dystonia, focal hand dystonia and truncal dystonia.

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.