We aim to understand whether tremor may be an intrinsic feature of juvenile myoclonic epilepsy (JME) and whether individuals with JME plus tremor experience a different disease course. Thirty-one individuals with JME plus tremor (17 females, mean age = 33.9 ± 13.8 years) and 30 age of onset- and gender-matched subjects with JME (21 females, mean age = 26.8 ± 11.2 years) prospectively underwent clinical and neurophysiologic assessment, including tremor assessment and somatosensory evoked potentials (SEPs). All JME plus tremor subjects experienced postural and action tremor affecting bilateral upper limbs. Nine of 31 individuals (29%) with tremor were never exposed to valproate (VPA), and 14 of 31 (45.2%) were not using VPA at the time of clinical evaluation. Twelve of 31 (38.7%) patients with JME plus tremor were drug-resistant compared to four of 30 (13.3%) with JME (p = .024). The JME plus tremor subjects had higher numbers of previous childhood absence epilepsy (n = 6/31 [19.4%]), interictal epileptiform discharges (n = 30/31 [96.8%]), photosensitivity (n = 8/31 [25.8%]), and psychiatric comorbidities (n = 12/31 [38.7%]). Six of 31 (19.4%) individuals with JME plus tremor had giant SEPs (1/30, 3.3% with JME
p = .05, chi-squared test). The clinical features and decreased sensorimotor inhibition in the JME plus tremor group suggest that tremor might be a marker of disease severity rather than an epiphenomenon of VPA exposure.