A Positive ‘Pointing Test’ in a Parkinson’s Disease Patient

Abstract

Various clinical tests have been advocated to differentiate psychogenic tremor (PT) from organic tremor (OT). These include, for example, the change of tremor characteristics upon distraction, entrainment, co-activation or loading [1–3]. The “pointing test” was introduced more recently. In an elegant study, subjects with various types of tremor were instructed to perform a rapid unilateral ballistic movement towards a switch following a visual cue, while tremor was observed in the contralateral hand [4]. Subjects included 11 patients with resting tremor caused by Parkinson’s disease (PD), 10 patients with essential tremor (ET), seven with psychogenic tremor, and 10 normal volunteers who purposely imitated tremors. In all patients with psychogenic tremor and in all normal volunteers, the ballistic movement of one hand led to a transient cessation of tremor within the contralateral hand. This clinical observation was supported by polymyography. In contrast, the tremor did not cease in the two groups with organic tremor (patients with PD or ET). The authors suggested that this pointing test might have a relevant role for identifying psychogenic tremor [4]. Schwingenschuh et al. used a variant of the pointing test in their study- which was one test in a test battery- and partially reproduced these findings, showing a clear tremor pause during the pointing test in 5 of 12 patients with psychogenic tremor [5]. None of 25 patients with organic tremor showed such a tremor pause (test specificity: 100% ), although a decreased amplitude during contralateral ballistic movements was noted in four of these 25 patients. Such amplitude reductions during contra-lateral ballistic movements can also occur in PD patients [6], but complete tremor cessation during the pointing test has never been described for organic tremors. Here, we report an abnormal pointing test in a PD patient with a classic rest tremor, confirmed both clinically and using accelerometry, suggesting that the clinical utility of this test is imperfect.