Etiology, clinical characteristics, and treatment outcome in patients with isolated sixth cranial nerve palsy

Abstract

Background & Objective: Isolated sixth cranial nerve palsy was the most common isolated cranial nerve palsy causing extraocular muscle dysfunction. As magnetic resonance imaging (MRI) quality had improved and knowledge had grown in recent years, the etiology previously classified as idiopathic might be re-classified to be another in the current era, and some require specific treatments. We therefore studied the etiology, clinical characteristics, and treatment outcome in patients with isolated sixth cranial palsy in recent years.

Methods: The medical records of 88 patients with isolated sixth cranial nerve palsy visited at the Neurological Institute of Thailand from January 2013 to December 2020 were reviewed. Clinical and demographical data included age, gender, laterality, headache location, vascular risk factors, etiology, treatment, and prognosis were collected and analyzed.

Results: The most common etiology was microvascular ischemia (29.5%), followed by inflammation (25.0%), and vascular disorders (20.5%). Neoplasm, abducens palsy mimics and false localizing sign, and idiopathic were less common (13.6%, 6.8% and 4.5%, respectively). Compared to patient with sixth cranial nerve palsy from microvascular ischemia, those with inflammatory cause were younger (p<0.001), were more likely to have headache (p=0.004), and had better prognosis at 3 months (p=0.018).

Conclusion: Microvascular ischemia was the most common etiology of isolated sixth cranial nerve palsy. Age at onset and presence of headache were the important clues for distinguishing sixth cranial nerve palsy due to microvascular ischemia from inflammation. Prognosis was more favorable in inflammation than microvascular ischemia group. We suggest MRI scan to exclude other causes before making a diagnosis of microvascular ischemia or idiopathic.