Neuro-Ophthalmic Syndromes and Processing Speed in Multiple Sclerosis

Effect of methylphenidate on oculomotor function in individuals with multiple sclerosis: a pilot randomized placebo-controlled trial

Introduction

Individuals with multiple sclerosis (MS) frequently experience visual and oculomotor symptoms that may impact and confound neuropsychological assessments of information processing speed (IPS). In this study, we examined the effect of the psychostimulant methylphenidate on oculomotor function and the association between change in oculomotor speed and change in information processing speed.

Methods

We used a repeated measures crossover design in which a sample of 11 participants with MS were randomly assigned to one of two treatment arms: one that received methylphenidate for 4 weeks and another that received a placebo for 4 weeks. After a 7-day washout period, the treatments were crossed over. The King Devick test, the Symbol Digit Modalities Test, and the Paced Auditory Serial Addition Test were administered at baseline and after each of the two study arms.

Results

We found a significant improvement in oculomotor speed in the methylphenidate condition as compared to placebo. This improvement was significantly correlated with improvement on a visuomotor assessment of IPS (Symbol Digit Modalities Test), but no such association was found for an auditory-verbal assessment of IPS (Paced Auditory Serial Addition Test).

Discussion

These findings suggest that individuals with MS experience improved oculomotor speed while taking methylphenidate, which may, in turn, improve performance on assessments of IPS with visuomotor demands.

Visual and motor confounds on the symbol digit modalities test

BACKGROUND

Slowed information processing speed is the most prevalent cognitive symptom in persons with multiple sclerosis (MS). The most commonly used instrument to measure information processing speed in MS is the Symbol Digit Modalities Test (SDMT). However, visual, oculomotor, and oralmotor deficits are frequently observed in persons with MS, and performance on the SDMT relies on these visual and motor functions, in addition to cognition.

METHODS

The current study examined the relationship between the SDMT and the King-Devick Test (KDT). The KDT encompasses similar oculomotor and oralmotor demands as the SDMT but requires a smaller attentional load. One hundred and thirty participants with MS completed the oral version of the SDMT and the KDT. Ordinary nonparametric bootstrapped regression models were performed with 1000 bootstrapped samples. Bootstrapped confidence intervals (CIs) were bias-corrected.

RESULTS

KDT performance explained 31% (bootstrapped CI: 18 - 43%) of the variance of SDMT performance (moderate correlation), much more than demographic and disease-related variables (0.7% and 10%, respectively).

CONCLUSIONS

Visual, oralmotor, and oculomotor functions contributed significantly to SDMT performance. Therefore, these sensory and motor functions must be taken into account when interpreting SDMT scores.