Asian Journal of Research and Reports in Neurology

Background: Internuclear ophthalmoplegia (INO) is generally caused by a lesion in the medial longitudinal fasciculus, characterised by diminished adduction and contralateral abduction nystagmus. Reverse INO, or "INO of abduction," is a rare variation, often linked to elevated intracranial pressure but infrequently connected with intracranial hypotension.

Case Presentation: We present the case of a 39-year-old Indian female, BMI of 28 kg/m2 and no comorbidities, who presented with dizziness, postural headache, cervical pain radiating to the head, and diplopia lasting for 15 days after engaging in heavy lifting. The neurological examination indicated right lateral rectus palsy and horizontal right-beating nystagmus in the left eye during adduction, with no evidence of ptosis or pupillary irregularities. The MRI of the brain (1.5T) demonstrated enlarged dural venous sinuses and effacement of the optic nerve sheath, indicative of intracranial hypotension. The probable cause was a cerebrospinal fluid (CSF) leak originating from the cervical area. The patient displayed characteristics indicative of reverse INO, resulting from cranial nerve VI traction caused by low CSF pressure.

Discussion: Although abducens nerve palsy is typically associated with increased intracranial pressure due to its passage through Dorello’s canal, this case exhibited a reverse INO pattern generated by intracranial hypotension. This paradoxical presentation emphasises the vulnerability of the abducens nerve to both elevated and diminished pressure conditions and illustrates the diagnostic difficulty of reverse internuclear ophthalmoplegia in the context of CSF volume shifts.

Conclusion: Reverse INO may serve as an unusual yet indicative sign of intracranial hypotension. Awareness of this presentation is essential for prompt diagnosis and response, including therapeutic restoration of cerebrospinal fluid volume to avert additional neurological problems.