Frontal lobe dysfunction in multiple sclerosis as assessed by means of Lurian tasks : effect of age at onset

Abstract We investigated frontal cognitive function in a group of 153 patients with multiple sclerosis and 100 healthy controls using a global scale composed by a set of items from the Luria-Nebraska Neuropsychological Battery (LNNB) which has been validated by Malloy and colleagues on frontally damaged patients. A second scale was built with LNNB items tapping parietal lobes function. Patients who were specifically impaired on the frontal scale (12%) had a shorter disease duration and were less physically disabled than those failing on the parietal tasks (8.5%) or those showing combined deficits (21.5%). Sixty-four patients were also tested on the Wisconsin Card Sorting Test (WCST). Twenty-seven (37.5%) patients were found to be impaired on the WCST, but the latter could not predict reliably their performance on the LNNB frontal scale. We also examined whether age of onset and disease duration could have had any effect on the cognitive performance of selected groups of patients. We found that relative to normals, deficits on the frontal scale were more severe in patients with a clinical onset around age 20 than in patients with a later onset (i.e., around 35), the two groups being comparable for duration and degree of disability. Furthermore, patients with a longstanding illness (> 10 years) were more affected on visuospatial processing and frontal control of language than those with a short duration (1.5 yrs). We propose that a greater disease activity interacting with contingent (developmental?) factors is responsible for the appearance of transient frontal deficits in several young MS patients. A differential involvement of long associative and connecting bundles is also proposed as a basis for understanding the pattern of cognitive deficits encountered in selected patient groups.