Ocular Neuromyotonia in Thyroid Eye Disease

Ocular neuromyotonia (ONM) in thyroid eye disease (TED) seems to be a rare finding. We present the case of a 61-year-old male TED patient who developed spontaneous transient neuromyotonic infradeviation of the right eye every   ~1 minute in the setting of prominent enlargement of the right inferior rectus muscle and restriction of supraduction. Neither carbamazepine or lacosamide were able to abate ONM. Following subsequent TED worsening with almost complete restriction of the right eye, ONM was no longer observed. ONM has been described in 7 TED cases, either in conjunction with underlying restrictive strabismus or in isolation. Chronic compression and inflammation seem to lead to nerve hyperirritability, demyelination, and/or axonal damage and predispose to ONM in TED. Importantly, ONM might develop during active or inactive TED. Voltage gated sodium channel blockers should be used in TED-related ONM, albeit clinical response might be incomplete, suggesting the presence of other mechanism(s), besides ephaptic transmission. Newer neuronal membrane stabilizers acting on sodium and calcium channels (e.g. lamotrigine, oxcarbazepine) as well as newer monoclonal antibodies (e.g. teprotumumab, tocilizumab, infliximab) might play a role in TED-related ONM and their potential therapeutic effect should be investigated in future studies.