Bilateral Internuclear Ophthalmoplegiaand Horizontal Gaze Palsy Secondary to Pontine Infarct in a Young Adult With Hyperhomocysteinaemia: A Rare Case Report

Internuclear ophthalmoplegia (INO) is a rare eye movement disorder caused by lesions of the medial longitudinal fasciculus (MLF). Bilateral INO (BINO) with horizontal gaze palsy is even rarer and indicates an extensive brainstem lesion involving both MLFs and the paramedian pontine reticular formation (PPRF). While multiple sclerosis is the commonest cause of bilateral INO in young adults, vascular causes must always be ruled out. We report the case of a 36-year-old previously healthy man who presented with sudden-onset binocular horizontal diplopia, bilateral adduction deficit with abducting nystagmus, bilateral horizontal gaze palsy, and bilateral lower motor neuron facial palsy. MRI revealed a non-haemorrhagic dorsal pontine infarct involving the MLFs and PPRF. Fundoscopy showed right eye retinal infiltrates, raising suspicion of a microvascular event. Further workup found marked hyperhomocysteinaemia, an under-recognised but reversible risk factor for thrombotic stroke in young patients. The patient was managed with dual antiplatelets, statins, B-vitamin supplementation, ocular surface protection, and orthoptic therapy. He showed partial recovery with normalisation of serum homocysteine at three months. This case highlights the need to consider vascular and metabolic causes, such as hyperhomocysteinaemia, in young adults presenting with bilateral INO. Early detection and correction of modifiable risk factors can improve outcomes and prevent recurrence.