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Abstract
Objective To disentangle the different forms of postural tremors in Parkinson disease (PD).
Methods In this combined observational and intervention study, we measured resting and postural tremor characteristics in 73 patients with tremulous PD by using EMG of forearm muscles. Patients were measured both “off” medication (overnight withdrawal) and after dispersible levodopa-benserazide 200/50 mg. We performed an automated 2-step cluster analysis on 3 postural tremor characteristics: the frequency difference with resting tremor, the degree of tremor suppression after posturing, and the dopamine response.
Results The cluster analysis revealed 2 distinct postural tremor phenotypes: 81% had re-emergent tremor (amplitude suppression, frequency difference with resting tremor 0.4 Hz, clear dopamine response) and 19% had pure postural tremor (no amplitude suppression, frequency difference with resting tremor 3.5 Hz, no dopamine response). This finding was manually validated (accuracy of 93%). Pure postural tremor was not associated with clinical signs of essential tremor or dystonia, and it was not influenced by weighing.
Conclusion There are 2 distinct postural tremor phenotypes in PD, which have a different pathophysiology and require different treatment. Re-emergent tremor is a continuation of resting tremor during stable posturing, and it has a dopaminergic basis. Pure postural tremor is a less common type of tremor that is inherent to PD, but has a largely nondopaminergic basis.
Glossary
- BIC=
- Bayesian Information Criterion;
- EDC=
- extensor digitorum communis;
- ET=
- essential tremor;
- FCR=
- flexor carpi radialis;
- MDS-UPDRS=
- Movement Disorders Society Unified Parkinson's Disease Rating Scale;
- PD=
- Parkinson disease;
- TFR=
- time frequency representations
Footnotes
↵* These authors contributed equally to this work.
Go to Neurology.org/N for full disclosures. Funding information and disclosures deemed relevant by the authors, if any, are provided at the end of the article.
Editorial, page 581
- Received July 21, 2017.
- Accepted in final form December 4, 2017.
- © 2018 American Academy of Neurology
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