Spectral Analysis of Lithium Tremor

INTRODUCTION: Lithium has proven efficacy in bipolar affective disorder (BAD) but induces tremor as a side effect in a quarter of patients. Lithium tremor (LT) shares some clinical characteristics of essential tremor (ET) and Parkinson’s disease tremor (PT), which might cause difficulties in differential diagnosis. Furthermore, current knowledge of LT is lacking detailed electrophysiological characterization. Here, we present detailed spectral attributes of accelerometric tremor recordings as a diagnostic tool for LT. METHODS: 10 patients (7 males, 3 females) between ages of 29–68, who were on lithium for BAD for 2–12 years, were evaluated for hand tremor with the spectral analysis of accelerometric recordings with different postures. Tremor severity was rated clinically on WHIGET (Washington Heights-Inwood Genetic Study of Essential Tremor) scale. Results were analyzed in comparison to results of ET (n=19) and PT (n=19) patients from our database. RESULTS: LT was most prominent at extensor postures with an average peak frequency (PF) of 8.0±0.3 Hz and an extremely low amplitude, high harmonic components and high noise level. The average PF of LT was similar to that of ET (7.3±0.4 Hz), but higher than that of PT (5.3±0.2 Hz) (p<0.0001). With weight loading, the PF of LT showed an increase of 1.3 Hz. Average amplitude of PT was higher than that of both LT and ET (p<0.0001); harmonic components of LT was comparable to PT whereas noise levels were similar to that of ET. Mean WHIGET score of LT (6.5±0.5) was significantly lower than that of ET (13.1±1) (p<0.0001). CONCLUSION: Electrophysiological features detected by accelerometry may help in differential diagnosis of LT from ET and PT.