Increased cortical hyperexcitability and exaggerated myoclonus with aging in benign adult familial myoclonus epilepsy.

The clinical implications of enlarged early cortical components of somatosensory evoked potentials in benign adult familial myoclonus epilepsy remain unknown. Somatosensory evoked potentials following electrical stimulation of the median nerve at the wrist were studied in 16 patients with a clinical diagnosis of benign adult familial myoclonus epilepsy (7 men and 9 women; mean age, 51 ± 18 years) and 19 age-matched apparently healthy control subjects (11 men and 8 women; mean age, 49 ± 18 years). Giant somatosensory evoked potentials were observed in 13 of the 16 patients. P25 and N35 amplitudes in the patient group were 11.4 ± 6.1 and 19.2 ± 11.5 μV, respectively, and both were significantly larger compared with those in control subjects (P = 0.008 for P25 and P < 0.0001 for N35). There was a significant positive relationship between age at somatosensory evoked potential examination and N20, P25, and N35 amplitudes, both in the patient and in the control groups (P < 0.05). The linear regression gradient of the N35 amplitude with respect to age was significantly larger in the patient group than in the control group (P = 0.04). Furthermore, regression analysis showed a significant positive relationship between the myoclonus rating scale and age at time of somatosensory evoked potential examination (R = 0.645, P = 0.007). Somatosensory evoked potential amplitude increased with age in patients with benign adult familial myoclonus epilepsy to a greater extent than in the control subjects, which suggests a progressive increase in cortical excitability based on progressive pathophysiology in benign adult familial myoclonus epilepsy.