The onset of amyotrophic lateral sclerosis.

Two patients in whom both the neurological examination and electromyography (EMG) were normal prior to the onset of amyotrophic lateral sclerosis (ALS) are reported. In each patient, the onset of ALS some 18 months later was clearly defined clinically and confirmed by subsequent EMG studies. These unique observations show that ALS commences at a defined time, and that there is early generalisation with an initial phase of rapid progression.