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 during routine neurologic examination. Therefore, brief screening 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 the SDMT. Bayesian statistics showed that a total score of 55 or lower on the SDMT accurately categorized 72% of patients, yielding sensitivity of 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.

Screening Instruments for the Early Detection of Cognitive Impairment in Patients with Multiple Sclerosis

“…First, only 21% of patients were impaired on the SDMT, which is relatively low compared with other studies. 10,45 Second, neither the duration of MS symptoms nor the participants' level of physical disability was reported, which, therefore, could limit the ability to compare the findings with those of other studies or to interpret them in a clinical context. Future research should use very large samples (thousands of patients), fully characterized, for better representativeness of the study sample and generalizability of results instead of the relatively low number of participants currently reported in most studies.…”

“…Because processing speed is a primary deficit in individuals with MS, the SDMT may be a particularly good candidate for cognitive screening purposes; previous studies have found it to be effective. 10 Similar to the batteries mentioned previously herein, however, the SDMT does not provide information on real-life outcomes.…”

“…It typically measures processing speed 9 and is one of seven tests that compose the MACFIMS. Because this test takes only 5 minutes to administer and is effective for screening purposes, 10 it was a good candidate for determining whether this single test could accurately correspond to the derived CI. Raw scores were used to make it easier for nurses to administer and interpret results.…”

Clemastine fumarate as a remyelinating therapy for multiple sclerosis (ReBUILD): a randomised, controlled, double-blind, crossover trial

“…We obtained safety laboratory measures including transaminases, triglycerides, creatinine, and thyroid-stimulating hormone concentrations at each visit. We assessed cognition with the symbol digit modality test (SDMT) that is sensitive to both cognitive dysfunction in multiple sclerosis 29 and cognitive dysfunction associated with excessive anticholinergic treatment in the elderly. 30 We assessed fatigue via the multidimensional assessment of fatigue (MAF) scale.…”

“…LCLA is the best-assessed and most well validated functionally relevant psychophysical clinical trial outcome for multiple sclerosis. 26,29 This clinical effect was confounded by a learning effect observed for LCLA assessments over the course of the trial. This made detection of clinical effects of the drug more difficult.…”