Re-emergent tremor of Parkinson's disease

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Abstract
OBJECTIVE To characterise postural tremors in patients with Parkinson’s disease. Rest tremor is a well recognised cardinal symptom of Parkinson’s disease, but postural tremors associated with the disease may cause more disability than the more typical rest tremor. Postural tremor of Parkinson’s disease has been attributed to enhanced physiological tremor, clonus, or coexistent essential tremor. It is postulated that one type of postural tremor in Parkinson’s disease represents a rest tremor that re-emerges after a variable delay while maintaining posture, hence “re-emergent tremor”. METHODS Accelerometry, peak frequency, peak frequency amplitude, root mean square (RMS) amplitude, and latency were determined in 18 patients (mean age: 63.2 (SD 9.8) years) with Parkinson’s disease who had clinically evident postural tremor, 20 (mean age: 66.9 (SD 5.8) years) with typical essential tremor, and seven (mean age: 68.7 (SD 15.3) years) with the combination of pre-existing essential tremor and subsequent Parkinson’s disease (essential tremor/Parkinson’s disease). Latency, the time interval starting with the assumption of an outstretched posture and ending with the onset of postural tremor, was measured by marking the start time by a pulse produced from interrupting a beam to a photocell when the arm reached a horizontal position. RESULTS The latency for the re-emergent tremor (9.37 (SD 10.66) s), present in 12 of 18 patients with Parkinson’s disease, was significantly (pCONCLUSION These studies suggest that the re-emergent tremor of Parkinson’s disease can be differentiated from the postural tremor of essential tremor and that it may share pathophysiological mechanisms with the more typical rest tremor.