Neuroimaging and acute ocular motor mononeuropathies: a prospective study.

OBJECTIVE To evaluate the necessity of neuroimaging in patients with acute, isolated ocular motor mononeuropathies. METHODS A prospective case series evaluating diagnostic technology results in 93 patients older than 50 years with acute isolated mononeuropathies was performed. Patients were included in the study if they had new-onset diplopia with an isolated cranial neuropathy (cranial nerve III, IV, or VI palsy) and no other signs of neurologic dysfunction. All patients had gadolinium-enhanced magnetic resonance imaging (MRI). The number of patients with lesions noted on MRI and the overall cost of imaging the patients were determined. Cost analysis of the MRI was conducted using Current Procedural Terminology codes and Medicare costs in 2010 dollars. Cost utility was estimated using cost data as well as published utility values for adults with diplopia and sex-specific life tables for life expectancy in the United States. RESULTS Four of 93 patients had lesions on MRI; however, only 1 of the 93 patients had a lesion related to the cranial mononeuropathy. The total modeled cost of imaging for these 93 patients was $131,688 to determine an underlying cause in 1 patient with no change in treatment. The estimated cost utility for the patient with a causative lesion found by MRI was $90.19 for diagnosis alone. CONCLUSIONS It may not be medically necessary to perform MRI scanning on every patient with an isolated cranial nerve III, IV, or VI palsy. In adults older than 50 years with an isolated mononeuropathy, physicians should carefully review the patients' history and findings to determine which patients to image at the initial evaluation.