In a recent consensus statement on tremor, the task force of the International Parkinson and Movement Disorder Society proposed a new term, ‘essential tremor-plus (ET-plus)’ which includes patients with the characteristics of essential tremor (ET) and additional soft neurological signs of uncertain significance such as questionable dystonic posturing. The clinical interpretation of questionable dystonia has been left to the investigator. The consensus statement also stated that the ET-plus syndrome does not include other clearly defined syndromes like dystonic tremor. However, the boundary between questionable dystonia and definite dystonia is not distinct leading to diagnostic uncertainty in a clinical setting. A similar case may be classified as ET-plus by one observer and dystonic tremor by another. Following the new definition, many studies have reclassified their ET cohort, and they have highlighted the problem of defining questionable dystonia in the diagnosis of ET plus. ET-plus is likely to be a mixture of patients that actually have dystonia and those that don’t, and clinically all we can do is to be suspicious that there might be dystonia. For example, it is not clear whether we should consider spooning and index finger pointing as a sign of questionable or definite dystonia. There are major research and possible therapeutic implications of questionable dystonia in the diagnosis of ET-plus. The concept of ET-plus is extremely difficult to implement without definite guidelines. The resolution will need a biomarker such as physiology or imaging.

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An 18-year-old boy presented with a 5-year history of brief episodes of involuntary, random, flinging movements of all 4 limbs and trunk lasting for 30 to 60 seconds. These episodes were precipitated by sudden movements, occurring multiple times per day, and were preceded by unpleasant sensations with preserved consciousness. He did not have any history of epilepsy. His father and elder brother had similar complaints. The clinical examination of the patient between the episodes was normal. The typical attack showed a choreoballistic movement with dystonic posturing involving all 4 limbs, trunk, neck, and face (Video S1). There was no difference in the triggers inducing mild and severe attacks. Based on the phenomenology of the abnormal movements, positive family history, and specific trigger factor, a clinical diagnosis of paroxysmal kinesigenic dyskinesia (PKD) was made. Magnetic resonance imaging of the brain and electroencephalography were normal. On whole-exome sequencing, a heterozygous single base pair insertion in exon 2 of the PRRT2 gene (chr16:g.29825015_29825016insC; depth: 23×) that results in a frameshift and premature truncation of the protein 8 amino acids downstream to codon 217 (p.Arg217ProfsTer8; ENST00000567659.1) was detected (Fig. 1). The observed variation has previously been reported in patients affected with PKD. 1 He was started on carbamazepine tablets (200 mg 2 times daily), resulting in a significant reduction (1-2 per week) in the frequency of attacks at the 1-month follow-up. The doses of carbamazepine FIG 1. Integrated genome viewer snapshot showing the variation (chr16:g.29825015_29825016insC; c.640_641insC; p.Arg217ProfsTer8) in exon 2 of the PRRT2 gene detected in heterozygous condition in the patient.

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