Practice parameter: The usefulness of evoked potentials in identifying clinically silent lesions in patients with suspected multiple sclerosis (an evidence-based review)

Abstract

The Quality Standards Subcommittee of the American Academy of Neurology (AAN) is charged with developing practice parameters for neurologists for diagnostic procedures, treatment modalities, and clinical disorders.The selection of topics for which practice parameters are used is based on prevalence, frequency of use, economic impact, membership involvement, controversy, urgency, external constraints, and resources required.This article addresses the usefulness of evoked potentials (EPs) in identifying clinically silent lesions in patients with suspected MS.The diagnosis of MS remains primarily clinical, requiring evidence of white matter lesions disseminated in space and time. 1,2Some patients with suspected MS not fulfilling clinical dissemination criteria (MS suspects) have abnormal EPs that identify clinically unsuspected lesions. 3,4Current diagnostic criteria allow MS suspects to be reclassified into definite MS categories if EPs identify clinically silent lesions. 2,5The identification of clinically unsuspected lesions is one major reason clinicians use EPs in MS suspects. 4,6resumably, MS suspects with EP-identified clinically silent lesions are more likely to have MS and are at higher risk for developing MS-related disabilities.Accurately identifying these high-risk patients will become increasingly important if early therapies are demonstrated to be effective in preventing or delaying disability in patients with MS.To determine the effectiveness of EP-identified silent lesions in diagnosing MS, we performed a systematic review and analysis of the literature.Based on this review we propose practice parameters for the use of EPs in patients with suspected MS.Process.Confirmation of the ability of EP-identified clinically silent lesions to diagnose MS requires a comparison with an independently verifiable gold standard. 7Potential gold standards include pathologic confirmation of MS lesions, brain MRI, or the eventual development of clinically definite MS (CDMS).Pathologic confirmation in MS suspects is not usually practical given the invasiveness of brain biopsy. 8The lack of specificity of MRI 9 limits its usefulness as a gold standard.We concluded that the eventual development of CDMS was the best available independent gold standard to evaluate the usefulness of EP-identified silent lesions in MS suspects.To find articles describing the relationship between EP findings and the development of CDMS, we searched the National Library of Medicine's Medline database for articles published from 1966 to January 1998, using the terms multiple sclerosis and evoked potentials.We subsequently screened the search result articles and their bibliographies for articles discussing EPs in the diagnosis of MS.We selected those studies that followed MS suspects evaluated with EPs for the development of CDMS.We eliminated articles that did not employ standard EP techniques. 10rom the articles fulfilling these criteria we abstracted the following methodologic characteristics: the method and setting of cohort assembly, number of patients studied, duration of follow-up, clinical and demographic features of the patients, and the criteria used to define CDMS.Based on these methodologic characteristics, we graded the studies Class I to IV using the diagnostic test strength-of-evidence rating scheme appended to this report (see below).For each EP technique studied we calculated the following parameters: sensitivity-the proportion of MS suspects developing CDMS with abnormal EPs; specificity-the proportion of MS suspects not developing CDMS with normal EPs.We also calculated the positive predictive value (PPV)-the proportion of MS suspects with abnormal EPs developing CDMS; and the complement of the negative predictive value (NPVc)-the proportion of MS suspects with normal EPs developing CDMS.Additionally, we determined the relative rate that patients with abnormal EPs developed CDMS as compared to patients with normal EPs by dividing the PPV by the NPVc.As an overall measure of the strength of the association between EP results and eventual CDMS, we calculated Goodman and Kruskal's tau. 11(In the current

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• American Academy of Neurology US

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