A special kind of anterior horn cell involvement in juvenile myoclonic epilepsy demonstrated by macro electromyography.

Juvenile myoclonic epilepsy (JME) is not an uncommon seizure disorder, occurring in 5-10% of epileptic patients. A subclinical anterior horn cell involvement has been suggested in some JME patients by concentric needle electromyography (EMG) and turn/amplitude analysis. In this study, 22 JME patients and 17 normal control subjects have been studied with macro EMG, which is a sensitive method to assess the size of motor units. Most JME patients (19 of 22) had a pathologically increased number of individual large macro motor unit action potentials (MUAPs) compared to control subjects. For both biceps brachii and tibialis anterior muscles, means of median macro MUAP amplitudes were significantly greater than those of normal controls, whereas the fiber density values were only slightly increased. This suggested another kind of anterior horn cell involvement in JME than seen in motor neuron diseases.