l-Dopa in dystonia: A modern perspective.

"Every child exhibiting dystonia merits an l-dopa trial, lest the potentially treatable condition of dopa-responsive dystonia (DRD) is missed" has been a commonly cited and highly conserved adage in movement disorders literature stemming from the 1980s. We here provide a historical perspective on this statement, discuss the current diagnostic and therapeutic applications of l-dopa in everyday neurologic practice, contrast these with its approved indications, and finish with our view on both a diagnostic and therapeutic trial in children and adults with dystonia. In light of the relatively low prevalence of DRDs, the large interindividual variation in the required l-dopa dose, the uncertainty about an adequate trial duration, the substantial advances in knowledge on etiology and pathophysiology of these disorders, and the availability of various state-of-the-art diagnostic tests, we think that a diagnostic l-dopa trial as a first step in the approach of early-onset dystonia (≤25 years) is outdated. Rather, in high-resource countries, we suggest to use l-dopa after biochemical corroboration of a defect in dopamine biosynthesis, in genetically confirmed DRD, or if nigrostriatal degeneration has been demonstrated by nuclear imaging in adult patients presenting with lower limb dystonia. Furthermore, our literature study on the effect of a therapeutic trial to gain symptomatic relief revealed that l-dopa has occasionally proven beneficial in several established "non-DRDs" and may therefore be considered in selected cases of dystonia due to other causes. In summary, we argue against the application of l-dopa in every patient with early-onset dystonia and support a more rational therapeutic use.