To report a patient with isolated unilateral sixth nerve palsy as a symptom of nasopharyngeal carcinoma.

Nasopharyngeal carcinoma is an aggressive tumor which is difficult to manage. Common clinical exhibitions are cervical masses, bloody nasal discharge, ear symptoms and cranial nerve palsy. In patients suffering from cranial nerve palsy, fifth and sixth nerves are the most commonly affected. However, isolated unilateral sixth nerve palsy is a rare symptom of nasopharyngeal carcinoma in the skull base and few such cases have been reported in the literature so far.

The patient was a 54-year old female with a four-month history of dizziness and occasional horizontal diplopia who had lost weight significantly over this period. She had no history of smoking. The patient reported no visual loss or jaw claudication recently. She showed a right abduction deficit. Alternate cover testing at distance revealed an esotropia of the right eye in primary gaze, which was amplified in right gaze. Other ophthalmological and neurological examinations were normal. Magnetic resonance imaging (MRI) of the brain and orbits with and without gadolinium showed a large heterogeneously enhancing mass in the right aspect of the nasopharynx that extended to the level of the cavernous sinus and right internal carotid artery. Both orbits appeared normal. Endoscopic biopsy of this mass, by an otolaryngologist, revealed squamous cell carcinoma and the patient underwent radiotherapy with an adjacent chemotherapy regimen.

Isolated sixth nerve palsies in adults over the age of 50 are usually ischemic; but in enduring cases, neoplastic processes should be considered. This entails medical and paramedical (especially brain and orbital imaging) evaluation.