Abnormal neuropsychological findings are not necessarily a sign of cerebral impairment: A matched comparison between chronic fatigue syndrome and multiple sclerosis

Objective: The aim of this study was to assess the potential impact of effo rt in comparative studies assessing neurocognitive dysfunction in patients with and without a neurologic diagnosis. Background: It was hypothesized th at a subgroup within a group of patients with prominent neurocognitive comp laints but without a neurologic diagnosis would have impaired performance o n a task originally designed to detect malingering. Method: We compared the neuropsychological performance of a group of 40 patients with a definite d iagnosis of multiple sclerosis (MS) with that of 67 patients with chronic f atigue syndrome (CFS). The Amsterdam Short-Term Memory Test, a forced-choic e memory task, served as measure to detect submaximal effort. In addition, we administered a regular neuropsychological task generally considered to b e sensitive for cognitive deterioration. Results: Compared with the MS grou p (13%), a larger proportion of the matched CFS group (30%) obtained scores indicative of reduced effort. In contrast, the proportions of patients sco ring below the cutoff value on a conventional neuropsychological test did n ot differ significantly (17% of MS patients and 16% of CFS patients). Concl usions: The results obtained raise the question of to what extent abnormal test findings in the absence of documented neurologic impairment should be interpreted as a sign of cerebral impairment. The suggestion has been made to screen more often for biased results in comparative research studies so as to enhance valid interpretation of neuropsychological findings.