Eye and hand motor interactions with the Symbol Digit Modalities Test in early multiple sclerosis

Abstract

Purpose Eye and hand motor dysfunction may be present early in the disease course of relapsing-remitting multiple sclerosis (RRMS), and can affect the results on visual and written cognitive tests. We aimed to test for differences in saccadic initiation time (SI time) between RRMS patients and healthy controls, and whether SI time and hand motor speed interacted with the written version of the Symbol Digit Modalities Test (wSDMT). Methods Patients with RRMS (N=44, age 35.1±7.3 years), time since diagnosis <3 years and matched controls (N=41, age 33.2±6.8 years) were examined with ophthalmological, neurological and neuropsychological tests, as well as structural MRI (white matter lesion load (WMLL) and brainstem lesions), visual evoked potentials (VEP) and eye-tracker examinations of saccades. Results SI time was longer in RRMS than controls (p<0.05). SI time was not related to the Paced Auditory Serial Addition Test (PASAT), WMLL or to the presence of brainstem lesions. 9 hole peg test (9HP) correlated significantly with WMLL (r=0.58, p<0.01). Both SI time and 9HP correlated negatively with the results of wSDMT (r=−0.32, p<0.05, r=−0.47, p<0.01), but none correlated with the results of PASAT. Conclusions RRMS patients have an increased SI time compared to controls. Cognitive tests results, exemplified by the wSDMT, may be confounded by eye and hand motor function.