The utility of MRI in suspected MS: Report of the Therapeutics and Technology Assessment Subcommittee

To the Editor:

We read with interest the Report of the Therapeutics and Technology Assessment Subcommittee of the AAN.1 The Subcommittee concludes that in patients with a typical clinically isolated syndrome the finding of even a few (three, perhaps even one) white matter lesions on a T2-weighted MRI scan is a more sensitive predictor of the subsequent development of clinically definite multiple sclerosis (CDMS) than the fulfillment of more stringent criteria as recommended by the International Panel on the diagnosis of MS.2 However, it is also suggested that this increased sensitivity can be achieved without sacrificing specificity, a statement that we consider incorrect.

In the studies they reviewed, several biases can be identified, 3 including those due to patient selection like referral bias, patient filtering bias, and spectrum bias. Although these biases do not necessarily affect the internal validity of a study, they limit the clinical applicability, which is crucial for the purpose of the recommendations. Another bias is induced by the large number of patients lost to follow-up. Because the gold standard is the diagnosis of CDMS verified during follow up, loss to follow-up is a source of verification bias. Because sensitivity and specificity estimates are …