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  • Updated 09.18.2019
  • Released 08.31.1995
  • Expires For CME 09.18.2022

Limb dystonia

Introduction

Overview

Limb dystonia is a type of dystonia consisting of involuntary contractions of the arms or legs associated with abnormal posturing, repetitive movements, and functional impairment. In this article, the authors review current knowledge on limb dystonias. They review updates on the classification, genetics, and pathophysiology of limb dystonia. The main clinical features of limb dystonia together with advances in the etiology, pathogenesis, and treatment of limb dystonia are also reviewed.

Key points

• Limb dystonia is classified as primary if dystonia is the only presenting symptom or as secondary if associated with additional neurologic signs and an underlying cause is identified or suspected.

• Early-onset primary dystonia (before 26 years of age) is rare, usually affects 1 or both lower limbs, and often generalizes, whereas adult-onset primary dystonia is relatively common, typically starts in the upper limbs, and remains focal.

• Writer’s cramp is the most common task-specific upper limb dystonia.

• Suspected secondary limb dystonias should prompt a search for structural brain lesions and heredo-metabolic causes (eg, Wilson disease or neurodegeneration with brain iron accumulation).

• Limb dystonia may be the initial presenting sign in neurodegenerative disorders like Parkinson disease, progressive supranuclear palsy, and corticobasal ganglionic degeneration.

• Abnormal plasticity in the somatosensory cortex and loss of inhibition at spinal and cortical levels together with environmental factors like repetitive injury hold a key role in the pathophysiology of dystonia.

• Limb dystonia is successfully treated with botulinum toxin injections or deep brain stimulation.

Historical note and terminology

The term dystonia is defined as a sustained, involuntary contraction of muscle that produces an abnormal posture and frequently causes twisting and turning. The task specificity and presence of sensory tricks make dystonia unique among other neurologic symptoms. In 1830, Charles Bell described hand dystonia in professional writers followed by Gowers’ description of dystonia in musicians. Oppenheimer described generalized dystonia in the early 20th century, naming it dystonia musculorum deformans (22). As dystonia is not a disease of muscle, the term primary torsion dystonia is now preferred (78). Over the last 90 years, the classification of this disorder has evolved from a clinical characterization, such as focal, segmental, or generalized dystonia, to encompass a parallel molecular biological dimension with acknowledgement of affected chromosomal loci, mutated proteins, and biochemical dysfunctions.

Writer's cramp, a task-specific and common condition, underscores many difficulties in the diagnosis of this disorder. Historically, patients may initially notice tightness or stiffness with writing prior to diminished writing speed and cramping with prolonged writing. The cramping of the hand will be present only with writing and will disappear almost immediately after stopping this activity. Physical examination of affected patients frequently reveals normal findings, except when performing certain tasks or adopting a certain posture. As a result of this, the condition was once thought to be of psychogenic origin (72). Fortunately, increasing electrophysiological studies and documentation of abnormal findings in patients with limb dystonia have improved the acceptance of this disorder as one resulting from neurologic mechanisms (26; 11).

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