Tremor Differentiation on Surface Electromyography

Objective: The aim of this study was to differentiate tremors on the basis of the electromyographic examination. Methods: A total of 100 patients, having different kind of tremors were prospectively analyzed. A detailed neurological and electromyographic examination was performed. The tremor was studied in all limbs positions. Clinically, patients were divided into seven diagnostic groups fulfilling the respective diagnostic criteria; Parkinson’s disease (n= 45), Essential tremor (n=33), Psychogenic tremor (n =07), Valproate induced tremor (n =07), Cerebellar tremor (n =03), Primary writing tremor (n =03) and Rubral tremor (n = 02). Results: On surface electromyography tremors were divided into two groups: with synchronous and alternating pattern in the antagonist muscles. Tremor frequency may be useful for differentiation of low (less than 4 Hz) frequency tremors (Rubral tremor) and high (more than 9 Hz) frequency tremors (Valproate induced tremor) but not useful for tremors falling in middle frequency range (4 – 9 Hz) i.e Essential, PD, Cerebellar, Psychogenic and Primary writing tremors. Tremor amplitude is much variable and is not useful in tremor differentiation. Tremor burst pattern is also not useful as both synchronous and alternate pattern can be seen in a particular type of syndromic diagnosis. Tremor burst duration is a more reliable parameter for tremor differentiation. Conclusion: If the electromyographic tremor examination is used in addition to the clinical criteria for tremor differentiation there will be no significant difficulties for tremor differentiation.