The Signature of Primary Writing Tremor Is Dystonic

Background It has been debated for decades whether primary writing tremor is a form of dystonic tremor, a variant of essential tremor, or a separate entity. We wished to test the hypothesis that primary writing tremor and dystonia share a common pathophysiology. Objectives The objective of the present study was to investigate the pathophysiological hallmarks of dystonia in patients affected by primary writing tremor. Methods Ten patients with idiopathic dystonic tremor syndrome, 7 with primary writing tremor, 10 with essential tremor, and 10 healthy subjects were recruited. They underwent eyeblink classic conditioning, blink recovery cycle, and transcranial magnetic stimulation assessment, including motor-evoked potentials and short- and long-interval intracortical inhibition at baseline. Transcranial magnetic stimulation measures were also recorded after paired-associative plasticity protocol. Results Primary writing tremor and dystonic tremor syndrome had a similar pattern of electrophysiological abnormalities, consisting of reduced eyeblink classic conditioning learning, reduced blink recovery cycle inhibition, and a lack of effect of paired-associative plasticity on long-interval intracortical inhibition. The latter 2 differ from those obtained in essential tremor and healthy subjects. Although not significant, slightly reduced short-interval intracortical inhibition and a larger effect of paired-associative plasticity in primary writing tremor and dystonic tremor syndrome, compared with essential tremor and healthy subjects, was observed. Conclusions Our initial hypothesis of a common pathophysiology between dystonia and primary writing tremor has been confirmed. Primary writing tremor might be considered a form of dystonic tremor. (c) 2021 International Parkinson and Movement Disorder Society

Automated summary

The study found that primary writing tremor and dystonic tremor syndrome share similar patterns of electrophysiological abnormalities, supporting the hypothesis of a common pathophysiology between them.