An electrical impedance spectroscopy (EIS) system for the detection of tissue abnormalities in amyotrophic lateral sclerosis (ALS). In particular, a EIS probe is disclosed having a three dimensional array of electrodes separated from one another in the x, y and z coordinates by quantitative separation distances. A first electrode set and a second electrode set comprising at least two electrodes are arranged in first and second x-y planes separated by a distance in a z direction, the distance is known quantitative value. A set of flanges 105 can be used to provide the predefined quantitative separation distance required.
