Is MRI Necessary for Older Patients with Isolated Palsy of Cranial Nerves III, IV, or VI?

A 70-year-old man with hypertension and diabetes presents with diplopia; physical exam reveals only an isolated sixth nerve palsy, and the patient is otherwise well. Is magnetic resonance imaging (MRI) necessary for this patient, whose probability of having a microvascular ischemic mononeuropathy is high?

To address this question, neuro-ophthalmologists evaluated a prospective series of 93 consecutive older adults (age, >50) with acute isolated palsy of the third, fourth, or sixth cranial nerve; all underwent gadolinium-enhanced MRI. Patients whose neurological examinations or medical histories suggested potential etiology other than ischemic mononeuropathy were excluded. MRI identified a causal lesion in only one case — a pontine hemorrhage…