The most plausible diagnosis in our patient without any prior medical or ocular history was isolated abducens paresis associated with COVID-19 infection. Vascular, neoplastic, and traumatic etiologies as well as pre-existing strabismus, thyroid eye disease, and myasthenia gravis were ruled out. A possible mechanism of the viral etiology in the current case is direct invasion of the abducens nerve. Prior CoV studies have described viral spread via the olfactory nerves possibly due a viral interaction with the membrane bound angiotensin-converting enzyme 2 receptor.5 Another hypothesized mechanism is hyperactivation of monocytes and dysregulated macrophages leading to a hyperinflammatory immune response.6 Given that the diplopia occurred at the beginning of our patient’s disease course, direct viral spread was suspected although an immune response to viral infection could not be ruled out.
Recently, diplopia has been suggested as a symptom of COVID-19 linked to ophthalmoparesis and Miller Fisher Syndrome, a demyelinating inflammatory polyneuropathy. Across three recent studies, one patient presented with partial third nerve palsy and accompanying bilateral sixth nerve palsy, one with complete third nerve palsy only, one with bilateral sixth nerve palsy, and two with unilateral sixth nerve palsy.,7,8,9 Similar to the two aforementioned cases, the precise mechanism in our case remains unknown. In these previously mentioned studies, patients who presented with third nerve palsy with or without additional sixth nerve palsy demonstrated a more severe manifestation of their infection and required more intensive, in-patient treatment. Whether we can provide a clinical guideline for future cases remains undetermined. However, the presentation and management of isolated ocular motor cranial nerve paresis, as in our case, may be associated with a less complicated disease process whereas patients who present with persistent sixth nerve palsy or additional third nerve palsy may be correlated with greater disease severity.
Since neuroimaging and cerebral spinal fluid analysis were not acquired for our patient who presented during the initial peak of the coronavirus pandemic, our conclusions are limited regarding the precise mechanism of the abduction paresis.
Treatment with azithromycin and hydroxychloroquine for 5 days per institutional protocol coincided with patient improvement and symptom cessation.