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Superior oblique myokymia (SOM)

Timothy C. Hain, MD Page last modified: April 18, 2009

Definition of SOM

Superior oblique myokymia is an unusual eye movement disorder where an eye muscle, the superior oblique, twitches periodically causing jumping of a single eye (Thurston and Saul 1991). It is probably caused by blood vessel compression of the trochlear (4th) nerve, at the root entry zone. (Hashimoto, Ohtsuka et al. 2004; Yousry, Dieterich et al. 2002);

Orbit
Anterior orbit showing superior oblique muscle (top left). Because the superior oblique inserts on the lateral side of the globe, it's main action is to intort (twist the eye so that the top pole moves inward). Image from http://upload.wikimedia.org/wikipedia/commons/c/cf/Eye_orbit_anterior.jpg

As the superior oblique inserts on the back, top and temporal side of the eyeball (globe) , the muscle's actions are to depress the eye, to intort it, and move it slightly laterally. These actions occur when the eye is positioned in the center of the orbit. The main action is intorsion. Intorsion means that the top of the eye twists inward (in the pulling direction of the SO)

The video here is of a patient diagnosed with left SOM, and who responded to both Tegretol as well as Timonal eye drops. It shows paroxysms of torsional eye movement, but the direction appears to be more of an extorsion, or at least an irregular combination of intorsion and extorsion. The camera is positioned over the left eye.

Treatment:

Both surgical and medical treatment are available. ( Mikami, Minamida et al. 2005; Williams, Purvin et al. 2007; Jain, Farooq et al. 2008)

SOM is conventionally treated with medications for neuralgia (such as oxcarbamazine). An eye drop (timoptic) has also sometimes been successful.

Surgery has occasionally been offered, involving neurovascular decompression. In our opinion, surgical treatment should be reserved for severe and medically intractable cases.

References:

Copyright August 3, 2016 , Timothy C. Hain, M.D. All rights reserved. Last saved on August 3, 2016