Clinical Neurophysiology Practice 4 (2019) 9–10 Contents lists available at ScienceDirect Clinical Neurophysiology Practice journal homepage: www.elsevier.com/locate/cnp Letter to the Editor Holmes’ tremor or functional tremor: Table 1 Neurophysiological criteria can help diagnosis Proposed neurophysiological criteria for the diagnosis of functional (psychogenic) tremor (Gironell, 2016). Definite functional A positive result for 1 of the following tests I read with much interest the case report ‘Holmes’ or functional tremor tremor?’ by Bocci and coworkers (Bocci et al., 2018) on a patient Intra-subject frequency variability with mixed rest and action tremor following intracranial dermoid Tremor suppression during attention distraction Probable functional A positive result for 3 or more of the following cyst surgery. Although the authors performed a neurophysiological tremor tests study, the final diagnosis was inconclusive. That case report Possible functional A positive result for 2 or fewer of the following reflects a classical clinical dilemma regarding the organic or func- tremor tests tional origin of movement disorders. In such cases, applying neuro- Loading test physiological criteria may help with diagnosis. Response to ballistic movements Coherence test There are indications regarding that patient that are suggestive Tonic coactivation of either type of tremor. The lag between surgery and tremor, the Tapping entrainment at 1 Hz intracranial congruent lesion (pontocerebellar angle) and the Tapping entrainment at 3 Hz mixed rest and action tremor would point to organic Holmes’ tre- Tapping entrainment at 5 Hz Tapping performance at 1 Hz mor. However, the tremor frequency variations, the frequency Tapping performance at 3 Hz entrainment induced by contralateral rhythmic tasks and the fact Tapping performance at 5 Hz that contralateral arm movement completely arrests tremor would suggest a functional origin. Not characteristic of Holmes’ tremor is the tremor frequency of 5–8 Hz (Holmes’ is typically <4 Hz (Deuschl et al. 1998), nor is the video of the patient (showing high We agree with Bocci et al. (2018) that routine electrophysiolog- frequency tremor and tremor suppression during attention distrac- ical testing results in a high degree of diagnostic certainty regard- tion). The authors conclude a possible co-existence of rubral tre- ing functional tremor. We emphasize that neurophysiological mor with psychogenic traits. criteria applied to functional tremor could help with tremor diag- Clinical and neurophysiological diagnosis of functional tremor nosis in routine clinical practice. is complex because of the great variability in clinical phenotypes (Lang and Voon, 2011). Another difficulty is that studies are typi- Conflict of interest cally performed for small series with few clinically documented patients – just 12, for instance, in Schwingenschuh et al. (2016). The content of this letter was obtained without any sponsorship Diagnosis may also be difficult when the patient has no previous or funding (industry, government or institutional), and Dr. A. Gir- psychopathology and when a functional movement disorder coin- onell reports no disclosures and no conflict of interest. cides with an organic disorder. Conceding all the above difficulties, I suggest an alternative References conclusion. Based on the Schwingenschuh et al. (2016) study and our own data (Gironell et al., 1997), we have proposed (Gironell, Bocci, T., Ardolino, G., Parenti, L., Barloscio, D., De Rosa, A., Priori, A., Sartucci, F., 2016) routine neurophysiological (accelerometry and surface 2018. Holmes’ or functional tremor? Clin. Neurophysiol. Pract. 3, 104–106. Deuschl, G., Bain, P., Brin, M., 1998. Consensus statement of the movement disorder EMG) criteria for the diagnosis of functional tremor as definitive, society on tremor. Mov. Disord. 13 (suppl 3), 2–23. probable or possible (Table 1). The neurophysiological tests we Gironell, A., López-Villegas, D., Barbanoj, M., Kulisevsky, J., 1997. Temblor use are intra-subject frequency variability, tremor suppression psicógeno: análisis clínico, neurofisiológico y psicopatológico. Neurología 12, during attention distraction, loading, response to ballistic move- 293–299. ments, coherence, tonic co-activation and trapping entrainment. Gironell, A., 2016. Routine neurophysiology testing and functional tremor: toward the establishment of diagnostic criteria. Mov. Disord. 31, 1763–1764. Functional tremor is considered definitive when there is intra-sub- Lang, A.E., Voon, V., 2011. Psychogenic movement disorders: past developments, ject frequency variability >1.5 Hz or tremor suppression during current status, and future directions. Mov. Disord. 26, 1175–1182. attention distraction (Table 1). Applying these criteria, we suggest Schwingenschuh, P., Saifee, T.A., Katschnig-Winter, P., Macerollo, A., Koegl-Wallner, that the patient reported by Bocci et al. (2018) may have definitive M., Culea, V., Chadery, C., Hofer, E., Pendl, T., Seiler, S., Werner, U., Franthal, S., Maurits, N.M., Tijsssen, M.A., Schmidt, R., Rothwell, J.C., Bhatia, K.P., Edwards, M. functional (psychogenic) tremor. In this case, brain surgery and the J., 2016. Validation of ‘‘laboratory-supported” criteria for functional lag between surgery and tremor would be a coincidence. (psychogenic) tremor. Mov. Disord. 31, 555–562. https://doi.org/10.1016/j.cnp.2018.11.003 2467-981X/Ó 2019 International Federation of Clinical Neurophysiology. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). 10 Letter to the Editor / Clinical Neurophysiology Practice 4 (2019) 9–10 ⇑ Alexandre Gironell Movement Disorders Unit, Department of Neurology, Hospital de la Santa Creu i Sant Pau, Autonomous University of Barcelona, Catalonia, Spain ⇑ Address: Department of Neurology, Hospital de Sant la Santa Creu i Sant Pau, Av. Sant Antoni Maria Claret, 167, 08025 Barcelona, Catalonia, Spain. E-mail address: agironell@santpau.cat Available online 25 January 2019