Essential tremor and cerebellar dysfunction - Clinical and kinematic analysis of intention tremor

The cerebellum is assumed to play a major role in the pathophysiology of es sential tremor (ET), As intention tremor is considered one of the classical features of cerebellar disease, we have assessed a large group of patients with ET for the semiology of the tremor and have performed objective quant itative analysis of a grasping movement in patients with ET, cerebellar dis ease and a normal control group. We found 25% of the patients to have a mod erate or severe kinetic tremor with clear-cut features of a classical inten tion tremor. Another 33% of the patients had a mild intentional component o f their kinetic tremor, Patients with intention tremor (ETIT) did not diffe r from those with. predominant postural tremor (ETPT) With respect to alcoh ol sensitivity of the tremor and the frequency of a family history. ETIT pa tients were older and more often showed head and trunk involvement. The ons et of this intention tremor has been assessed retrospectively, It was found to begin at a randomly distributed time interval after the onset of the po stural tremor, but older patients had a shorter time to intention tremor. Q uantitative accelerometry of postural tremor showed similar tremor frequenc ies in both patient groups, but ETIT patients had a slightly larger tremor amplitude. Quantitative analysis of a grasping movement using an infrared-c amera system was performed in two subgroups of the patients with ETPT and E TIT and control groups with cerebellar disease or normal subjects. The inte ntion tremor could be quantified objectively as an increased amplitude of c urvature during the deceleration and target phase of the movement. The ampl itude measurements of intention tremor were clearly abnormal and of compara ble magnitude for ETPT and cerebellar disease. Additionally, the patients w ith ETIT had a significantly slowed grasping movement during the decelerati on and target period. Hypermetria was significantly increased for the patie nts with ETIT and cerebellar disease. We conclude that intention tremor is a feature of ET. ETIT patients have abnormalities of their upper limb funct ion compatible with cerebellar disease. This suggests that patients with mo re advanced ET show abnormalities of cerebellar functions.