Opsoclonus in three dimensions: oculographic, neuropathologic and modelling correlates.

Opsoclonus is a dyskinesia consisting of involuntary, arrhythmic, chaotic, multidirectional saccades, without intersaccadic intervals. We used a magnetic scleral search coil technique to study opsoclonus in two patients with paraneoplastic complications of lung carcinoma. Eye movement recordings provided evidence that opsoclonus is a three-dimensional oscillation, consisting of torsional, horizontal, and vertical components. Torsional nystagmus was also present in one patient. Antineuronal antibody study revealed the presence of anti-Ta (Ma2 onco-neuronal antigen) antibodies in one patient, which had previously been associated only with paraneoplastic limbic encephalitis and brainstem dysfunction, but not opsoclonus, and only in patients with testicular or breast cancer. Neuropathologic examination revealed mild paraneoplastic encephalitis. Normal neurons identified in the nucleus raphe interpositus (rip) do not support postulated dysfunction of omnipause cells in the pathogenesis of opsoclonus. Computer simulation of a model of the saccadic system indicated that disinhibition of the oculomotor region of the fastigial nucleus (FOR) in the cerebellum can generate opsoclonus. Histopathological examination revealed inflammation and gliosis in the fastigial nucleus. This morphological finding is consistent with, but not necessary to confirm, damage to afferent projections to the FOR, as determined by the model. Malfunction of Purkinje cells in the dorsal vermis, which inhibit the FOR, may cause opsoclonus by disinhibiting it.