Limb dystonia including writer’s cramp

Limb dystonia can occur in primary dystonias or as a complication in neurodegenerative diseases e.g. Huntington’s disease, Wilson’s disease or Parkinson syndromes or other diseases like structural brain damage, peripheral trauma or drug-induced. Any muscle group under voluntary control can be affected, dystonic muscle overactivity can occur during rest, be aggravated by movement, or occur only during voluntary movement (action dystonia). If the dystonia is triggered by a specific task, it is called “task-specific” dystonia and affects mostly the hand. As task-specific dystonia causes most disability and is the greatest therapeutic challenge, this summary will focus mainly on this form of limb dystonia. Exercises with a repetitive movement pattern such as writing, typing or playing musical instruments are predestinated to this type of dystonia (1). Co-contraction of agonist and antagonist muscles lead to abnormal postures and movements sometimes associated with tremor or myoclonic jerks. This leads to disability in occupations with repetitive fine motor tasks. The underlying pathophysiology why some individuals develop such a task-specific dystonia and others not, despite of maybe excessive overuse of the hand remains unclear. Safety and efficacy of botulinum toxin has been well established during decades of use (2).