Isolated Sixth Nerve Palsy as a First Presentation of Nasopharyngeal Carcinoma: A Case Series

Purpose: To describe isolated sixth nerve palsy as an uncommon presentation of nasopharyngeal carcinoma (NPC). Patients and Methods: We analyzed the demographics, clinical presentation, neuroimaging findings, and pathological examination results of the nasopharyngeal masses of patients diagnosed with isolated sixth nerve palsy due to NPC. Results: Isolated sixth nerve palsy as the first presenting sign of NPC was diagnosed in five patients. Two patients were aged <50 years and three were aged >50 years, and one of these three older patients had vascular risk factors. Most of the patients in our case study had an uncommon presentation of isolated sixth nerve palsy with diplopia, followed by typical NPC signs such as a neck lump (two patients), nasal obstruction (two patients), tinnitus (two patients), hearing loss (one patient), and epistaxis (one patient). Pathological examination revealed non-keratinizing NPC in all cases. Neuroimaging showed that the sites of tumor invasion were the clivus, Dorello's canal, and cavernous sinus, which explained the sixth nerve palsy. One patient whose NPC had progressed to the orbital apex later developed other cranial nerve palsies. Three patients underwent concurrent chemoradiotherapy (CCRT), and one patient underwent CCRT with adjuvant chemotherapy. The last patient was unfortunately lost to follow-up. The symptoms of four patients who underwent treatment improved. Conclusion: Isolated sixth nerve palsy can be the first presentation of NPC, especially in patients aged <50 years old without microvascular risk factors or even in patients aged >50 years old with microvascular risk factors. This case study emphasizes that a thorough clinical history and careful physical and neuroimaging examinations might be necessary to rule out life-threatening conditions in patients with isolated sixth nerve palsy.