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  1. Rest tremor due to hypoglycaemic injury?

    Title Page: Rest tremor due to hypoglycaemic injury? 1Halil Onder, 2 Javid Jahanroshan

    1Department of Neurology, Yozgat State Hospital, Yozgat, Turkey 2Department of Neurology, Hacettepe University Hospital, Turkey

    Corresponding author: Halil Onder Department of Neurology, Yozgat State Hospital, Yozgat, Turkey Post Code: 66000 Telephone number: 4442066 email: halilnder@yahoo.com

    Key words: Hypoglycaemic injury; Rest tremor; Neuroimaging; Pathophysiology. Manuscript word count: 555

    Rest tremor due to hypoglycaemic injury? Letter to Editor: We read with great interest the article by Boylan et al. in which they report an interesting patient with severe hypoglycaemic injury presenting with continuous symmetric low amplitude 3-4 Hz pill-rolling type rest tremor of both hands (1). We agree with the interesting aspect of this patient, however, I would like to comment on the article for a better understanding of the report and avoid misleading conclusions. First, as the authors state, rest tremor in deep coma is an unexpected finding as only one prior case has been reported showing rest tremor in a patient following brain death (2). Therefore, for reporting such an atypical presentation, detailed documentation of the clinical manifestations is crucial to make a proper diagnosis. For instance, propriospinal myoclonus, a form of spinal myclonus is known to involve limbs with a frequency of 1-6 Hz which is similar to the frequency range of the described movements in this case (3). Another type of myoclonus is anoxic myoclonus that is a widely recognized finding after cardiac arrest and viewed as an ominous sign (4). Remarkably, myoclonus has also been reported to be present in hypoglycaemic encephalopathy in addition to hypoxic brain injury (5, 6). Although the underlying mechanisms and responsible neurons are not properly understood, generally, myoclonus has been associated with abnormal function of either cortical and/or subcortical structures (7). On the other hand, epileptiform discharges have been reported to lead anoxic-myoclonus in some sub-group of patients and EEG monitoring is suggested to be performed in early anoxic myoclonus for determination of underlying possible ictogenesis well as neuroprognostication of the patients (4, 8). Taken together these knowledges, we think that diagnosing the defined movement disorder (low- amplitude, 3-4 Hz) as 'rest tremor' can be strictly challenging. Hence, we think that electrophysiologic evaluation of the defined symptoms in this patient might give substantial contributions in identification of the abnormal movements in terms of phenomenological aspect. Also, EEG recording which is lack in the report might also give important insights regarding the underlying mechanisms as also mentioned by Elmer et al (4). Based on these points, we think that there may be some crucial limitations in the documentation of this manifestation, as tremor video was unavailable in the report. Second, I would like to remark the devastating neuroimaging findings, affecting prominently striatum, cerebral cortex (including occipital cortex) and hippocampus. However, unlike hypoxic damage, occipital cortex and hippocampus have rather been resistant to hypoglycaemic injury (9), which was not the case in this case. Hence, I wonder if the authors might state if there had been a concurrent hypoxic injury or not in this case. Finally, although the points mentioned above need to be clarified, I agree with the strictly interesting aspect of this report mentioning a patient with rest tremor due to hypoglycaemic injury. As there are some major hypotheses trying to explain the pathophysiology of rest tremor, such as basal ganglia and the cerebello-thalamo-cortical circuitry dysfunctions, the exact mechanims remain to be unknown (10). Besides, rest tremor occurring secondary to a brain lesion is an extremely rare entity, as not a detailed documentation of such a patient is present in literature. Future reports of these rare manifestations of movement disorders in symptomatic circumstances may add substantial contributions to our currently understanding of underlying pathophysiologies. Bullet Points - Were electrophysiologic evaluations of the defined movement disorders conducted? - Might a video demonstration of the defined 'rest tremor' be involved ? - Might the authors state if there had been a concurrent hypoxic injury or not in this case?

    Acknowledgements: None. Conflict of interest: None. References 1. Boylan LS. Hypoglycaemic injury spares thalamus, spoils striatum and leaves only a rest tremor. BMJ Case Rep. 2016;2016. 2. Araullo ML, Frank JI, Goldenberg FD, Rosengart AJ. Transient bilateral finger tremor after brain death. Neurology. 2007;68(16):E22. 3. Kojovic M, Cordivari C, Bhatia K. Myoclonic disorders: a practical approach for diagnosis and treatment. Ther Adv Neurol Disord. 2011;4(1):47 -62. 4. Elmer J, Sandroni C. A nuanced view of post-anoxic myoclonus. Resuscitation. 2017;115:A4-A5. 5. Kida Y, Sawada T, Naritomi H, Kuriyama Y, Ogata J, Kashiwagi A, et al. [A case of hypoglycemic coma associated with myoclonus, periodic synchronous discharges and progressive cerebral atrophy resembling Creutzfeld-Jakob disease]. Nihon Naika Gakkai Zasshi. 1988;77(3):419-24. 6. Nicoli F, Bartolomei F, Swiader L, Gastaut JL. [Diffuse, segmental, asynchronous myoclonus, manifestations of severe hypoglycemia]. Presse Med. 1991;20(36):1783-4. 7. Gupta HV, Caviness JN. Post-hypoxic Myoclonus: Current Concepts, Neurophysiology, and Treatment. Tremor Other Hyperkinet Mov (N Y). 2016;6:409. 8. Aicua Rapun I, Novy J, Solari D, Oddo M, Rossetti AO. Early Lance-Adams syndrome after cardiac arrest: Prevalence, time to return to awareness, and outcome in a large cohort. Resuscitation. 2017;115:169-72. 9. Cho SJ, Minn YK, Kwon KH. Severe hypoglycemia and vulnerability of the brain. Arch Neurol. 2006;63(1):138. 10. Helmich RC, Hallett M, Deuschl G, Toni I, Bloem BR. Cerebral causes and consequences of parkinsonian resting tremor: a tale of two circuits? Brain. 2012;135(Pt 11):3206-26.

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