Mystery case: superior oblique myokymia due to vascular compression of the trochlear nerve.

A 37-year-old man with episodic oscillopsia for 3 months showed intermittent torsional-vertical oscillation of the left eye (video on the Neurology® Web site at www.neurology.org). MRI revealed an attachment between left trochlear nerve and left superior cerebellar artery in the quadrigeminal cistern (figure). Gabapentin 600 mg twice a day ameliorated the ocular oscillation and oscillopsia. Superior oblique myokymia (SOM) causes monocular oscillopsia or torsional diplopia due to involuntary contractions of the superior oblique muscle. SOM may develop in association with pathologies involving the brainstem or vascular compression of the trochlear nerve in the subarachnoid space. In refractory patients with SOM, medications or microvascular decompression may be considered.