Opsoclonus is similar to ocular flutter, but is characterised by multidirectional back-to-back saccades of varying amplitude and direction. The bursts are erratic, very-high-frequency (10 to 25 cycles per second), high-velocity, back-to-back saccades that have no intersaccadic intervals between subsequent saccades.
As with all saccadic intrusions, these movements are usually not continuously present, but occur sporadically and are often provoked by shifting gaze. The eye movements are most often large enough (1 degree to 5 degrees) to see easily on clinical examination, but may occasionally be of very low amplitude1.
Pathogenesis
Flutter and opsoclonus are associated with pathology affecting either the pons,where burst neurons that control horizontal saccades are located, or the cerebellum. It is likely that increased GABA-A receptor sensitivity is present in a circuit involving the cerebellum, inferior olives, and brainstem saccadic premotor burst neurons.
Inherent properties of the saccadic burst neurons themselves predispose them to oscillating, and ion channel dysfunction of burst neurons is also proposed as a contributory mechanism1.
Causes
- Paraneoplastic conditions: associated with the following antibodies: amphiphysin, anti–neuronal nuclear antibody type 2 (ANNA-2, or anti-Ri), Hu (ANNA-1), Yo, Ma, P/Q-type calcium channel, N-methyl-D-aspartate (NMDA) receptor, GAD, and GQ1b (particulararly, nephroblastoma in children, and small cell carcinoma of the lung and carcinoma of the breast and uterus in adults).
Antineuronal antibodies, including anti-Ri, and a cancer screen, are indicated in patients with opsoclonus. - Brainstem encephalitis (including HIV)
(vv)Opsoclonus.mp4(tt)
(Video courtesy of Dr L Gwaunza, University of Zimbabwe)