Cognitive impairment in motor neuron disease with bulbar onset

Twenty-three patients with bulbar onset motor neuron disease/amyotrophic lateral sclerosis (MND/ALS) were clinically assessed. They subsequently underwent serial neuropsychological testing, event-related potentials (ERP) and SPECT studies. Cognitive impairment was defined by clinical evidence of dementia (DSM-IV and frontal evaluation) or by significant alteration indicated by neuropsychological testing (excluding patients with depression and major anxiety), or both.

Eleven patients (48%) were found to be cognitively impaired. Abnormalities indicated fronto-temporal involvement, with memory impairment, alteration of judgement and reasoning, reduced speech, behavioural dyscontrol and alteration of daily living activities. This impairment correlated well with event-related potentials and SPECT studies. Event-related potentials were the most sensitive test as 100% of the impaired patients had abnormal ERP (p = 0.04). The cognitively impaired group differed from the other group mainly by gender ratio (male/female) with an important male predominance: 1.75 vs. 0.33. MND/ALS was also more severe when cognitive decline was present.

This study adds further arguments for a cognitive impairment in MND/ALS. This also reinforces the hypothesis that there is continuum between MND/ALS and fronto-temporal lobe dementia.