Patient looking up to induce myokymia and then looking straight ahead, demonstrating extorsional eye movement.
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Chinskey ND, Cornblath WT. Inferior Oblique Myokymia: A Unique Ocular Motility Disorder. JAMA Ophthalmol. 2013;131(3):404–405. doi:10.1001/2013.jamaophthalmol.365
Author Affiliations: Department of Ophthalmology and Visual Sciences, W. K. Kellogg Eye Center (Drs Chinskey and Cornblath) and Department of Neurology (Dr Cornblath), University of Michigan, Ann Arbor.
Superior oblique myokymia is a well-described disorder in which patients have monocular, high-frequency, low-amplitude contractions of the superior oblique muscle producing torsional or vertical oscillopsia. These episodes often last seconds to hours and can occur several times a day. These movements can sometimes be induced by infraduction but otherwise occur spontaneously. The etiology of this disorder is unknown, although it is almost always benign. In recent years, some have suggested that superior oblique myokymia is due to vascular or nonvascular mechanical compression of the trochlear nerve at the root exit zone or is a primary brainstem disorder.1-5 However, in the vast majority of cases, no underlying cause is ever found. The clinical course is highly variable, ranging from spontaneous recovery to chronic oscillopsia and diplopia.6 Several therapies have been tried with varied success, including topical β-blockers, carbamazepine, phenytoin, baclofen, gabapentin, and, in severe cases, incisional surgery.1 We describe a unique form of myokymia involving monocular, high-frequency, low-amplitude contractions causing excyclotorsion, not incyclotorsion, induced by supraduction, suggesting an inferior oblique myokymia. Based on a PubMed search, this has not been described in the literature to date.
A 59-year-old man initially presented to our neuro-ophthalmology unit in 2003 with a 2-month history of brief episodes, lasting 30 seconds to 10 minutes, in which his right eye would quiver. During his initial evaluation, the patient was unable to reproduce the twitching movement. His symptoms were attributed to superior oblique myokymia based on his description of vertical jumping of his eye producing vertical oscillopsia. The patient was reassured that his condition was benign given the absence of other neurological features. He began treatment with gabapentin and was then lost to follow-up.
We describe a patient with intermittent, monocular excyclotorsion induced by looking up and out, all consistent with inferior oblique myokymia. This observation raises a number of interesting questions. In patients in whom a diagnosis of superior oblique myokymia is made clinically, as in our patient at his initial visit 8 years earlier, is inferior oblique myokymia actually the correct diagnosis?
The etiology of superior oblique myokymia is uncertain, with reports suggesting vascular compression of the trochlear nerve, direct involvement of the muscle, and brainstem disorders. In our case, there was no abnormality of other oculomotor nerve functions, perhaps lending support to this being a primary muscle problem.
In patients with a clinical history consistent with an ocular muscle myokymia and normal findings on examination, we suggest having the patient look up and out as well as up and in to try to provoke inferior oblique myokymia.