Visser, L. (Lisette) (2014) Essential tremor: a family of diseases? The familiality of clinical and electrophysiological characteristics in essential tremor. thesis, Medicine.
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Abstract
Introduction Essential tremor (ET) is mainly characterized by a bilateral postural and action tremor of the hands and forearms. Over the years it has become more apparent that ET is phenotypically heterogeneous disease; patients exhibit many associated findings and show overlap with other diseases, resulting in frequent misdiagnosis. These problems with diagnosing and defining ET may be the cause of the, to this extent, disappointing results in finding causal mutations. Many possible loci have been identified in different study populations but most are not confirmed and are even contradicted in other studies. Objective In order to move forward in genetic research, it is necessary to reconsider the definition of ET. We hypothesize that ET is not just one disease entity but rather a family of diseases: the essential tremors. The goal of this study is first to see how heterogeneous ET actually is. Secondly we investigate which clinical and electrophysiological characteristics are familial in order to identify subgroups of ET and to find features that can function as a biomarker in genetic research. Methods We studied the occurrence of clinical and electrophysiological characteristics in an index group of 23 ET patients and tested the familiality of these characteristics in the affected family members of two families with ET. Our main focus was on the following characteristics: alcohol responsiveness, age at onset, disease duration, visual analogue scale score, tremor rating scale score, tremor frequency, tremor variance, intention tremor, influence of distraction, influence of entrainment, influence of loading, coherence of EMG signals within one arm and coherence of EMG signals of the left and the right arm. Results Characteristics were heterogeneously present in our index group: 8 (N=23) showed intention tremor, 9 demonstrated signs of distraction and 7 had increase in tremor amplitude with loading. Coherence within one arm occurred in 19 subjects (N=20), and coherence in the left and right arm occurred in 5 subjects (N=20). In family 2 (N=5) none of the subject had a tremor that was responsive to alcohol. Also age at onset was relatively similar in all family members. In family 1 (N=4) intention tremor only appeared in the subjects with long disease duration, while increased amplitude with loading and coherence within the same arm, occurred in the subjects with the shortest disease duration. Discussion The presence of distraction in many subjects suggests that having a functional tremor symptom does not rule out an organic disease like ET. Alcohol unresponsiveness and age at onset seemed familial characteristics in family 2 suggesting the existence of an ET subgroup characterized by these features. Moreover it might suggest that these phenotype features could function as biomarkers for corresponding genetic alterations. The increase of intention tremor with disease duration, which we found in family 1, corresponds with findings in previous studies. The presence of increased amplitude with loading in subjects with short disease duration might suggest overlap between enhanced physiological tremor (EPT) and ET, and a possible tendency of ET to mimic EPT at an early stage. Conclusion We showed that the characteristics that we focused on in this research are heterogeneously present in ET patients. The characteristics age at onset and non-responsiveness to alcohol seemed to be familial in one of the families. This supports our hypothesis that ET is probably a family of diseases instead of one disease entity. Furthermore, it brings us a step closer to identifying subgroups of ET and finding biomarkers that will eventually help us to unravel the underlying genetic causes of ET.
| Item Type: | Thesis (Thesis) |
|---|---|
| Supervisor name: | Koning-Tijssen, Prof. Dr. M.A.J. de and Stouwe, Drs. A.M.M. van der |
| Faculty: | Medical Sciences |
| Date Deposited: | 25 Jun 2020 11:05 |
| Last Modified: | 25 Jun 2020 11:05 |
| URI: | https://umcg.studenttheses.ub.rug.nl/id/eprint/2516 |
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