Novel case of ocular neuromyotonia associated with thyroid-related orbitopathy and literature review.

Purpose: To present a novel case of pupillary involvement in ocular neuromyotonia (ONM), a rare ocular syndrome that causes intermittent diplopia because of an abnormal delay in extraocular muscle relaxation and to conduct a literature review.
Methods: A case report is presented to demonstrate clinical characteristics and treatment of ONM. In addition, a literature review is conducted by searching Medline and Embase databases. Data are collected from all known published cases listed in these databases to collate patient demographic data, presumed etiology or associated pathologies, and treatment strategies.
Results: The presented case demonstrates successful carbamazepine treatment of thyroid-related orbitopathy-associated ONM involving cranial nerve III. A review of the literature elicits 66 published cases of ONM, three of which were deemed to be associated with thyroid-related orbitopathy. The most common cause of reported ONM is suprasellar pathology, comprising approximately 60% of documented cases. Most published ONM cases (n = 41) were treated with carbamazepine, demonstrating a success rate of 87.8%. Of the published cases, cranial nerve III was involved 56% of the time, cranial nerve VI was affected in 39% of cases, and only 9% of ONM cases involved cranial nerve IV.
Conclusions: Ocular neuromyotonia is a rare cause of intermittent diplopia. Unlike most neurologic etiologies of diplopia, this syndrome can often be treated effectively with carbamazepine by stabilizing the neural cell membrane. To the authors' knowledge, this is the first presentation of ONM associated with thyroid-related orbitopathy, demonstrating bilateral but asymmetric miosis during episodes of muscle spasm.