Occasional essay: Upper motor neuron syndrome in amyotrophic lateral sclerosis

The diagnosis of amyotrophic lateral sclerosis (ALS) requires recognition of both lower motor neuron (LMN) and upper motor neuron (UMN) dysfunction.1 However, classical UMN signs are frequently difficult to identify in ALS.2 LMN involvement is sensitively detected by electromyography (EMG),3 but, as yet, there are no generally accepted markers for monitoring UMN abnormalities,4 the neurobiology of ALS itself and disease spread through the brain and the spinal cord.5 Full clinical assessment is therefore necessary to exclude other diagnoses and to monitor disease progression. In part, this difficulty regarding detection of UMN involvement in ALS derives from the definition of ‘the UMN syndrome’. Abnormalities of motor control in ALS require reformulation within an expanded concept of the UMN, together with the neuropathological, neuroimaging and neurophysiological abnormalities in ALS. We review these issues here.\n\n