Traumatic Pseudo-Internuclear Ophthalmoplegia Due to Suspected Medial Rectus Injury Following Orbital Trauma: A Case Report

Internuclear ophthalmoplegia (INO) is a classic neuro-ophthalmologic syndrome caused by disruption of the medial longitudinal fasciculus (MLF), resulting in impaired adduction of the affected eye and abducting nystagmus of the contralateral eye during horizontal gaze. However, an INO-like ocular motility pattern may occur without an MLF lesion, a phenomenon termed pseudo-internuclear ophthalmoplegia. Peripheral etiologies, including extraocular muscle injury, may produce similar clinical findings and pose a diagnostic challenge. A 34-year-old man presented after a motor vehicle accident with severe head trauma and loss of consciousness. Computed tomography revealed multiple skull fractures and epidural hemorrhage without evidence of brainstem injury. Ophthalmic examination showed limited adduction of the right eye that failed to cross the midline, with abducting nystagmus of the left eye on left gaze, mimicking internuclear ophthalmoplegia. Orbital imaging demonstrated a subtle medial orbital wall fracture without clear medial rectus entrapment. Given the absence of neuroimaging evidence of brainstem pathology and the presence of orbital trauma, traumatic injury to the medial rectus muscle was suspected. The patient was managed conservatively and showed gradual improvement in ocular motility and resolution of diplopia over two weeks. Traumatic pseudo-internuclear ophthalmoplegia is an uncommon but important differential diagnosis in patients presenting with INO-like ocular motility abnormalities after orbital trauma. Careful clinical examination and orbital imaging are essential to distinguish peripheral extraocular muscle injury from central MLF lesions.