Botulinum neurotoxin for writer’s cramp: A systematic review and illustrated guide

Abstract

Writer’s cramp (WC) is a focal task-specific dystonia that affects the fingers, hands, and forearms. It interferes with an individual’s ability to write, causing professional disability. In this systematic review, we discuss the epidemiology, pathophysiology, clinical features, and management of WC. In accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we included publications until February 5, 2022, from the PubMed database. In addition, we elaborate on the clinical assessment and selection of appropriate muscles for botulinum neurotoxin therapy through pictorial illustrations. The prevalence of WC is underestimated because medical attention is only sought by those with professional disability. The clinical presentation of WC is heterogeneous. In some patients, dystonia is manifested only during writing tasks (simple WC), while in others, several manual tasks are affected in addition to writing (complex WC). Some patients have semirhythmic movements of the hand with no apparent postural abnormality during writing (writing tremor). The assessment of the pattern of dystonia is confounded by the compensatory movements a patient adopts while writing. There are several pharmacological, nonpharmacological, and surgical options for the management of WC. However, there are no randomized controlled trials supporting the efficacy of oral medications. The efficacy of physiotherapy, occupational therapy, and noninvasive brain stimulation is debatable. Neurosurgical procedures, although reportedly effective, are seldom justified in focal task-specific dystonia. Botulinum neurotoxin is considered an effective treatment option based on several prospective studies and few randomized controlled trials. However, WC may be the most challenging indication for this therapy because writing is a complex manual task. Furthermore, given the heterogeneity, clinicians often face difficulties in discerning the exact abnormality and selecting the appropriate muscles for treatment.