Neurophysiological testing in the diagnosis of amyotrophic lateral sclerosis

Neurophysiological testing plays a very important role in the diagnosis of amyotrophic lateral sclerosis (known in the British world as motor neuron disease). As specified in the Awaji criteria, electromyography is critical for defining the neurogenic changes due to involvement of the lower motor neuron (LMN), and it can do so for muscles that are not involved clinically or are so only minimally. Demonstrating LMN involvement can be enhanced by the judicious use of neuromuscular ultrasound and imaging, particularly whole-body magnetic resonance imaging. There is a gap with involvement of the upper motor neuron (UMN), with promising procedures yet to be adopted widely. Reflex function can be used to demonstrate hyperreflexia and sometimes that paresis is at least partly of UMN origin. Protocols using transcranial magnetic stimulation can demonstrate enhanced excitability of interneuronal circuits in motor cortex and thereby pathology involving the UMN. The motivation behind studies using these and other techniques is to be able to make the diagnosis before the disease has spread significantly from its site of onset, when the clinical deficit is still minor.