Role of anterior and occipital white matter lesions for smooth eye tracking in myotonic dystrophy.

Background: The degradation of smooth pursuit eye movements (SP) in myotonic dystrophy (MD) has been shown to result from lesions in the central nervous system. Imaging and histopathological studies have shown considerable areas of white matter lesions (WMLs) with periventricular emphasis.

Objective: To discover which of these WMLs are relevant in SP impairment?

Method: Horizontal sinusoidal SP, the vestibulo-ocular reflex (VOR), and its suppression by fixation (VOR-S) were investigated in 12 patients with MD, and the data obtained were compared with those from a control group.

Results: Parallel degradation of SP and VOR-S was found in patients, although the eyes hardly needed to move with VOR-S. VOR in patients was normal. These results indicate a central rather than a peripheral origin for the SP degradation. Magnetic resonance images of the patients' heads were obtained and the WMLs transferred to a standard map. The lesions were mainly located around the occipital and anterior horn of the lateral ventricle. SP performance was then related to lesion site. The largest area of deficit associated lesions appeared to be in the parieto-occipital white matter. The most severe SP impairment, however, was associated with frontal WMLs.

Conclusion: The study establishes a link between SP deficits and WMLs in patients with MD, in line with previous observations that, not only parieto-occipital regions, but also the frontal cortex has a crucial role in the gain control of SP.