Distinguishing features between valproate-induced tremor and essential tremor.

BACKGROUND: Tremor frequently occurs in patients taking valproate and may resemble that observed in patients with essential tremor (ET). We aimed to compare the distribution, severity, and functional impact of both types of tremor.

METHODS: Among 118 consecutive individuals taking valproate, we identified 28 patients with valproate-induced tremor severe enough to require pharmacological treatment; through evaluations using the Clinical Rating Scale for Tremor (CRST), they were compared with 29 consecutive patients with ET.

RESULTS: Patients with valproate-induced tremor were significantly younger than those with ET: 35.6 ± 15.4 vs 58.8 ± 20.5 years (P < .001), with a shorter evolution time of tremor (P < .001). Total CRST scores did not differ between groups (P = .164), neither in subscores of Parts A (P = .321), B (P = .094), and C (P = .386). Patients with valproate-induced tremor had a higher proportion of postural tongue tremor compared with ET patients: 22 (79%) vs 15 (52%) (P = .034). A frank tremor axis in the Archimedes spirals was observed in a higher proportion of patients with ET compared to valproate-induced tremor: 31% vs 3.6% (P = .006).

CONCLUSIONS: Patients with valproate-induced tremor requiring pharmacological treatment have similar distribution, CRST scores, and functional impact than those with ET.