Isolated Trochlear Nerve Palsy After Severe COVID-19 Infection: A Case Report

Introduction Typically, COVID-19 presents as a respiratory illness, but it can also cause cranial and peripheral neuropathies, even months after initial infection [1]. We present a case of an isolated unilateral trochlear nerve palsy with vertical strabismus after severe COVID-19 infection. Case Presentation A 35-year-old male presented to the family physician’s office with complaints of worsening near vision, double vision while reading and blurred images. He had severe COVID-19 infection four months ago. Also, the patient had no systemic diseases or history of trauma. Visual acuity and visual fields were normal. Neurological examination revealed vertical diplopia when looking to the left, with the right eye deviating upward. Blood tests indicated normal complete blood count, CRP, FT4, TSH level and negative anti-AChR and anti-MuSK. A lumbar puncture revealed no abnormalities. Cerebral MRI showed asymmetry of the superior oblique muscles. On the right side the muscle was thinner (OD 0.2 cm vs. OS 0.31 cm). Based on these findings, a clinical diagnosis of the right trochlear nerve palsy and vertical strabismus was made. The treatment with glucocorticoids was initiated, but no significant improvement was observed. Inferior oblique muscle recession surgery was recommended for this patient. Discussion It is atypical that isolated trochlear nerve palsy developed in the absence of trauma or other common causes for healthy young adult [2]. This increases the possibility of COVID-19 infection as a contributing factor. Cranial nerve impairment has been associated with COVID-19 infection, however unilateral trochlear nerve palsy like in this case is a rare condition [3]. It is hypothesized that the IV cranial nerve damage can be caused by delayed immunemediated inflammation or by microvascular changes like micro-thromboses in small vessels [4]. Conclusions This case highlights the delayed development of trochlear nerve palsy with vertical diplopia occurring months after severe COVID-19 infection. Although we are unable to confirm that the trochlear nerve palsy in this patient was a direct consequence of COVID-19, we recommend monitoring of patients after this infection to identify and successfully manage late neurological or ocular complications.