Central eye movement abnormalities in patients with SMA types II and III

Spinal muscular atrophy (SMA) is a genetic neuromuscular disorder characterized by progressive motor neuron degeneration, leading to symmetrical proximal weakness, bulbar dysfunction, and respiratory involvement. Although extraocular muscles (EOMs) are typically spared, there are conflicting reports regarding oculomotor abnormalities in SMA. This study aimed comprehensively to assess eye movement function in patients with SMA types II and III using videonystagmography (VNG).

We included 18 SMA patients and 21 healthy subjects of similar ages and sexes. All participants underwent an otoscopic/audiological examination before the VNG recording. In VNG testing, we analyzed and compared optokinetic nystagmus (OKN), saccade parameters, and smooth pursuit movement (SPM) gain.

There were no statistical differences between the OKN gain and saccade velocity between groups. There was a lower percentage of saccade accuracy in the SMA group than in the control group (p = 0.017). SPM gain was lower in the SMA group than in the control group (p < 0.0001). The correlation analyses revealed a positive correlation between age and saccade latency (r = 0.613, p < 0.0001) and a negative correlation between age and SPM gain (r = -0.487, p = 0.003).

In this study, we performed a comprehensive evaluation of eye movement function with VNG in patients with SMA. Our findings indicate that while extraocular muscles remain unaffected in SMA, subtle central oculomotor control abnormalities-likely involving supranuclear and/or cerebellar pathways-may accompany the disease and can be quantitatively detected using VNG.