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Intermittent diplopia and strabismus caused by ocular neuromyotonia
Purpose:
Two cases illustrate the symptoms, signs, etiologies, and treatment of ocular neuromyotonia (ONM).
Methods:
The histories, neuroradiologic tests, and/or biopsy revealed the etiologies of ONM in both patients. Clinical observations, videotaping, and electronic eye movement recordings documented the eye movements.
Results:
A 72-year-old man with chronic arachnoiditis following myelography with thorium dioxide (Thorotrast) developed intermittent diplopia and a partial right third nerve palsy. Left gaze induced spasm of the right medial rectus. Right gaze produced right lateral rectus spasm. A 66-year-old woman, who had radiation treatment for a pituitary tumor and acromegaly, had intermittent spasm of the left medial rectus muscle and left esotropia. The episodes occurred spontaneously and were induced by right gaze. A left internuclear ophthalmoplegia was also found. Carbamazepine (Tegretol) abolished the ONM in both patients.
Conclusions:
Although ONM is an unusual cause of intermittent diplopia and strabismus, its distinctive clinical features identify it. Injury to the peripheral cranial nerves probably leads to segmental demyelination, axonal hyperexcitability, and a self-perpetuating, reverberating circuit, which causes spasms of the extraocular muscles.