Comparative impact of paraclinical studies in establishing the diagnosis of multiple sclerosis

Long-latency cerebral event-related potentials in multiple sclerosis

The objective of this study was to characterize electrophysiologically the basis of the cognitive dysfunction in multiple sclerosis. The cognitive dysfunction experienced by patients with multiple sclerosis has recently become more widely appreciated, but the best means of monitoring such function is unknown. Long-latency cerebral event-related potentials were recorded in a group of patients with relapsing/remitting or secondarily progressive multiple sclerosis and in a group of age-matched normal control subjects. Subjects were presented a series of auditory tones, with one (1,000 Hz) occurring during 86% of the trials (frequent tone) and the other (2,000 Hz) occurring during 14% of the trials (rare tone). Subjects were required to listen to the stimuli and count the occurrence of the rare tones. Cerebral responses recorded from the scalp were averaged separately for the rare and frequent tones. The N1, P2, N2, and P3 components of the long-latency response were all prolonged in latency in patients with MS, as were the N1-N2 and N1-P3 interpeak latencies. In addition, the amplitude of the P2 and P3 peaks was diminished in patients compared with control subjects. Significant correlations were found between the changes in both interpeak latency peak amplitude and the scores on the Mini-Mental State Examination. Electrophysiologic changes occur in MS that are the result of central disease (as opposed to involvement of primary afferent pathways) and correlate with cognitive status. The recording of event-related potentials may thus provide a useful tool, not only as an objective measure of cognitive function in patients with MS, but also as an aid in the evaluation of response to treatment.

A prospective study on the predictive value of CSF oligoclonal bands and MRI in acute isolated neurological syndromes for subsequent progression to multiple sclerosis

A prospective study in patients with a clinical acute isolated brainstem or spinal cord disorder was undertaken. The aim was to evaluate the predictive value of IgG intrathecal synthesis (through the detection of oligoclonal bands in CSF) and MRI lesions at presentation, for the subsequent progression to multiple sclerosis. Forty four patients took part in this study: 22 had a brainstem disorder and 22 a spinal cord disorder. After a mean period of 26 (SD 22) months, 30 patients (68.2%) developed clinically definite multiple sclerosis. The remaining 14 patients were followed up for more than seven years. Twenty six (59.1%) patients had oligoclonal bands in CSF, with a sensitivity of 80.0%, specificity of 85.7%, and a predictive value of 92.2%. Magnetic resonance imaging showed disseminated white matter lesions in 22 patients (50.0%), with a sensitivity of 60.0%, a specificity of 71.4%, and a predictive value of 81.7%. The difference between patients with multiple sclerosis and patients without the disease was statistically significant for the findings of an IgG intrathecal synthesis (P < 0.001). It was only borderline for the MRI findings (P = 0.052). Thus the detection of an intrathecal synthesis at presentation seemed to be a better prognostic indicator of the progression to multiple sclerosis in patients affected by acute isolated brainstem or spinal cord syndromes.

Diagnostic value of paraclinical tests in multiple sclerosis: relative sensitivities and specificities for reclassification according to the Poser committee criteria

The yield of paraclinical tests was evaluated in a prospective study of 189 consecutive patients referred for suspected multiple sclerosis (142 patients with multiple sclerosis, 47 non-multiple sclerosis patients on discharge). Patients were first classified according to the Poser criteria by the clinical findings. Subsequently, the results of paraclinical tests (cranial MRI, visually evoked potentials (VEPs), somatosensory evoked potentials by tibial nerve stimulation (SSEPs), motor evoked potentials (MEPs), and analysis of CSF for oligoclonal banding and IgG-index (CSF)) were taken into account. The percentage of reclassified patients (reclassification sensitivity, RS) was always lower than the percentage of abnormal results (diagnostic sensitivity, DS), and the divergence of RS v DS differed between the tests (60% v 84% in MRI, 31% v 77% in CSF, 29% v 37% in VEPs, 20% v 68% in MEPs, and 12% v 46% in SSEPs respectively). False reclassifications of non-multiple sclerosis patients to multiple sclerosis would have occurred with all tests (MRI: six of 47 patients, (reclassification specificity 88%); CSF: one (98%); VEPs: two (96%); MEPs: two (96%); SSEPs: four (91%); P < 0.05). Although MRI had superior diagnostic capacity, 57 of the 142 patients with multiple sclerosis were not reclassified by the MRI result, 12 of whom were reclassified by CSF and 18 by one of the evoked potential (EP) studies. Of the 98 patients not reclassified by CSF, 53 were reclassified by MRI and 39 by EPs. The results suggest that for the evaluation of paraclinical tests in suspected multiple sclerosis, comparison of diagnostic sensitivities is inappropriate. In general, a cranial MRI contributes most to the diagnosis; however, due to its comparatively low specificity and its considerable number of negative results, EP or CSF studies are often useful to establish the diagnosis of multiple sclerosis.