Analysis of the tremor in juvenile myoclonic epilepsy.

We aimed to investigate juvenile myoclonic epilepsy (JME) patients complaining of tremor unrelated to valproate (VPA) treatment and evaluate if there were differences between JME patients with and without tremor and essential tremor (ET) patients to exclude comorbidity.

Fifteen JME cases with the complaint of tremor, 14 JME patients without tremor, 14 patients with ET and 14 healthy subjects (HS) were included. Regularity, frequency and amplitude of the tremor and superimposed myoclonia were assessed by accelerometric analysis. Cortical SEPs evoked by the stimulation of the median nerve were recorded bilaterally. Clinical and neurophysiologic features were statistically compared between the groups.

Amplitude of postural tremor of the left hand was significantly increased in the ET group compared to JME patients with tremor, but there were no differences regarding to frequency. Strikingly, there were superimposed irregular, low-amplitude inconstant myoclonic jerks located to distal part of the fingers in JME group with tremor. Initial frequency of myoclonic seizures was also significantly higher in this group compared to JME patients without tremor but this difference disappeared after treatment. The group of JME with tremor had the highest N20-P25 and P25-N35 amplitudes, followed by JME without tremor, ET and HS, respectively.

Tremulous hand movements in JME resembled ET, but their amplitude was lower and characterized with accompanying irregular myoclonic jerks. The presence of tremor in JME patients should be taken into consideration to create more homogeneous groups in genetic and pathophysiological studies of JME.