Cognitive function in bulbar- and spinal-onset amyotrophic lateral sclerosis. A longitudinal study in 52 patients

We performed a longitudinal study of frontal and temporal lobe functions in patients with amyotrophic lateral sclerosis (ALS) and compared the evolution of cognitive performance with that of motor deficits in patients with spinal and bulbar-onset of the disease. Fifty two patients suffering from sporadic ALS according to the El Escorial criteria were examined; 37 patients had a spinal, 15 a bulbar onset of the disease. The data profile included examinations at entry (E1), every four months at follow-up (E2, E3, E4) and after 18 months (E5), if possible. Neuropsychological testing covered the domains of executive functions, memory and attentional control. ALS patients showed executive dysfunctions that were most prominently represented by deficits of non-verbal and verbal fluency and concept formation. Memory-related deficits were also present but less expressed. The same held true for phasic and tonic alertness and divided attention. In contrast to motor functions declining concomitantly with disease progression, cognitive deficits appeared in early disease, were essentially present at initial testing and did not substantially decline on follow-up. A subgroup analysis revealed that bulbar-onset ALS patients performed consistently poorer in many cognitive tests than spinal-onset ones with special reference to verbal and non-verbal fluency and interference control. This subgroup difference persisted or even increased throughout follow-up. We conclude that there is a fronto-temporal pattern of cognitive dysfunction in ALS expressing itself early in the course of the disease and mainly with bulbar forms. The cognitive deficits do not progress in synchrony with motor decline, but distinctly more slowly. We suggest that cognitive dysfunctions reflect functional and possibly morphological deficits outside the primary motor system that is specific for the nature and evolution of the disease and might also give clues to etiopathogenesis.