15. Does the selective membrane potential abnormality precede the onset of the ALS?

Abstract

Introduction In ALS patients, peripheral ion channel abnormality and membrane potential changes often exist. A recent study suggests selective membrane depolarization in some ALS patients. We performed the threshold tracking test in patient with upper motor neuron dysfunction. Patients Patient 1 is a 52-year-old man, whose chief complaint was gait disturbance for 4 years. He had no muscle weakness or fasciculations. Deep tendon reflexes (DTR) were exaggerated. The median CMAP amplitude was decreased (2.89 mV). EMG was normal except for multiplet of the quadriceps femoris. Patient 2 is a 69-year-old woman, whose chief complaint was dysarthria for 2 years. She had no muscle weakness or fasciculations. DTRs were exaggerated and jaw reflex was positive. Needle EMG showed chronic denervation only in the tongue. Result Two patients did not fulfill the criteria of ALS. We did threshold tracking in the median motor nerve. Target threshold CMAP amplitudes were set at 10%, 20%, 40% and 60% of the maximum CMAP. Both patients showed normal TE (threshold electrotonus) at 40%. The threshold changes by the hyperpolarizing current was small at the low target levels that suggests membrane depolarization. Conclusion Selective membrane depolarization may precede overt clinical and routine electrophysiological findings.