Clinical And Electrophysiological Characteristics Of Dystonia

Background and objectivesBoth dystonic tremor (DT) and essential tremor (ET) can be presented with head tremor with similar clinical manifestations. It is difficult to distinguish between them before the presence of other characteristic features. On the other hand, isolated head tremor (IHT) without any neurological signs is an obstacle in clinical diagnosis. Tremor analysis is based on surface electromyography (sEMG) and accelerometer, which serves as an import tool for tremor differential diagnosis. For the rarity of dystonic tremor, there were a handful researches into it in China. Botulinum toxin type A (BTX-A) local intramuscular injection is the first-line therapy for cervical dystonia (CD), but its effectiveness in DT has not been proven. The choices for BTX-A doses and inject sites usually depend on therapists. This study aims to:1. Compare the similarities and differences between DT and EHT;2. Provide insights into IHT diagnosis;3. By comparing tremor severity before and after therapy, explore the efficiency and safe dose of BTX-A in DT therapy.Method36DT patients,23EHT patients,15IHT patients and31age-gender-matched healthy volunteers were included. Clinical data and tremor analyses under different postures were obtained. A subgroup, of23DT patients was monitored2to4weeks after200-300U BTX-A therapy.Results1. Middle-aged females are vulnerable population of DT and EHT. Rest tremor presented in52.8%DT patients, while only prevailed in26.1%EHT (p<0.05);86.1%and13.0%patients complained of neck discomfort in DT and EHT group (p<0.05), separately.100%DT and52.2%EHT patients were aware of his/her head tremor (p<0.05). Family history of tremor was seen in47.2%and78.3%patients in each group, which was associated with earlier onset of tremor in EHT (p<0.05). mFTMTRS total score was significantly higher in DT patients (p<0.05) 2.There was no difference in sEMG presentation between DT and EHT. EHT demonstrated a frequency of5.63±1.09Hz, which was significantly higher than DT (4.96±0.65Hz,p<0.05). Tremor frequency and patients’ age were linearly related:ET frequency=5.68-0.02×age (p<0.05, R2=0.35) and DT=7.60-0.04×age(p<0.05, R2=0.44). Compared with control group, DT group was significantly asymmetry when rotating head to left and right side (p<0.05). Sensory trick was associated with a significant reduction in root mean square (RMS) in patients with DT (decrease by33%, p<0.05), but not in EHT (p>0.05).3. Rest tremor and neck discomfort were common in IHT.53.3%IHT patients had tremor family history, which was related to the severity of tremor (p<0.05). DT formula was better in predicting IHT frequency (p<0.05). Asymmetry was also noted in IHT (ARMS13.25±17.24μV), which was statistically significant when compared with EHT and control group (p<0.05).86%IHT had sensory trick, which was responsible for27%reduction in RMS.4.1n the subgroup of patients who received BTX-A therapy, Tsui score dropped from7.61±4.13to3.43±1.34points, including1-point decrease in tremor sub-score. Symptom recovery and side effect score were3.12±0.83and1.17±0.72,repectively.BTX-A therapy had no impact on tremor frequency but was able to reduce50%RMS. Sensory trick could lower33%RMS before and after therapy.Conclusion1. Compared with EHT patients, the proportion of patients with rest tremor, neck discomfort and awareness of head tremor is higher in DT. DT is also related to longer tremor duration and severity.2.DT and EHT can’t be distinguished by EMG results. Frequency of EHT and DT fluctuates around5.6Hz and4.9Hz, separately. Both decrease with age. Asymmetry and sensory trick are common features of DT. Sensory trick can decrease33%RMS before and after BTX-A therapy.3.IHT with the following features should be considered as DT:awareness of head tremor, presence-of neck discomfort and rest tremor, a positive sensory trick, and asymmetry tremor. Tremor analysis serves as a useful tool in differentiation, especially when the clinical picture is obscure.4.200-300U BTX-A is efficient in DT with reduction of50%RMS. It is proved to be safe and well tolerated in DT patients.