Superior Oblique Myokymia Caused by Vascular Compression in the Peripheral Trochlear Nerve: A Case Report

We report the first case of microvascular decompression (MVD) performed for superior oblique myokymia (SOM) caused by vascular compression of the peripheral trochlear nerve, leading to successful resolution of symptoms.

A 46-year-old man with no significant medical history experienced intermittent fluttering sensations in his left eye for 6 years. Initial examinations revealed an intorsional microtremor diagnosed as SOM. Conventional brain MRI showed no abnormalities. Despite using anticonvulsants with no relief, his condition worsened. A more detailed MRI revealed compression of the peripheral trochlear nerve by a branch of the superior cerebellar artery. MVD surgery was recommended. A lateral supracerebellar infratentorial approach was used during MVD surgery. The compressed nerve was identified and relieved by wrapping the compressing branch in Teflon felt and repositioning it. After the surgery, the symptoms ceased immediately, and the patient was discharged within a week. Although he initially had mild trochlear nerve palsy with double vision on downward gaze, this resolved within 9 months without recurrence at the 22-month follow-up. Previous cases treated with MVD showed symptom relief, although some experienced temporary nerve palsy. No deaths were reported from the procedure.

MVD is an effective treatment method for SOM that can occur not only at the root exit zone of the trochlear nerve but also due to peripheral trochlear nerve compression.