Screening for cognitive impairment in multiple sclerosis using the Symbol Digit Modalities Test

Abstract

Cognitive impairment is common in multiple sclerosis (MS), yet difficult to detect duringroutine neurologic examination. Therefore, briefscreening tests that identify patients who may benefit from a more thorough assessment or treatment are needed. We investigated the utility of the Symbol Digit Modalities Test (SDMT) as a screen for cognitive dysfunction because it can be administered and scored in about 5 minutes. One hundred MS patients and 50 healthy controls, matched on demographic variables, participated in the study. Examination procedures included the neuropsychological (NP) tests included in the Minimal Assessment of Cognitive Function in MS (MACFIMS) battery. Patients were considered impaired if they performed one and a half standard deviations below controls on two or more MACFIMS variables, excluding theSDMT. Bayesian statistics showed that a total score of 55 or lower onthe SDMT accurately categorized 72% of patients, yielding sensitivityof 0.82, specificity of 0.60, positive predictive value (PPV) of 0.71, and negative predictive value (NPV) of 0.73. These results suggest that the effectiveness of the SDMT as a screen for cognitive impairment in MS is roughly equal to that of other psychometric and questionnaire methods.