Differential diagnosis and management of acquired sixth cranial nerve palsy

Cranial nerve VI innervates the lateral rectus muscle. A lesion will result in esotropia greater at distance and an ipsilateral abduction deficiency. After the age of 50 years, vascular diseases are the most commonly known causes.

A 55-year-old white man reporting a 2-week history of horizontal diplopia that was worse at distance was found to have a left sixth cranial nerve paresis. The patient was diagnosed with hypertension and placed on medications. At the 4-week follow-up visit, the abduction deficiency had resolved.

The incidence of sixth nerve palsy is 11.3 in 100,000. A lesion anywhere along the course of the nerve, from the pons to the orbit, can cause a paresis or palsy. After ruling out trauma and non-neurological problems, cases should be classified into neurologically isolated or non-neurologically isolated cases. Neurologically isolated sixth nerve palsies are associated most commonly with vascular disease. Non-neurologically isolated sixth nerve palsies typically are associated with more grave conditions.

A sixth nerve palsy of vascular or undetermined causes typically resolves within 6 to 8 weeks. If resolution does not occur within 2 to 3 months, the condition progresses, or if additional neurologic signs or symptoms develop, imaging studies are indicated.