Is Neuroimaging Needed to Assess Acute Oculomotor Nerve Palsies?

Abstract & Commentary

Source: Chou KL, et al. Acute ocular motor mononeuropathies: Prospective study of the roles of neuroimaging and clinical assessment. J Neurol Sci. 2004;2129:35-39.

This paper reports the results of a prospective study of patients aged 50 years and older with acute isolated third, fourth, and sixth nerve palsies. The need for immediate neuroimaging in these patients was evaluated. Chou and colleagues prospectively evaluated 66 patients. They attempted to determine the need for neuroimaging as well as the role of clinical assessment in determining etiology. They investigated the rapidity of onset of the cranial nerve palsies. They found that the time to maximal diplopic symptoms was not predictive of etiology and that there was a median of 2 days for both peripheral microvascular and other etiologies. The presence of peripheral vascular risk factors such as diabetes mellitus, hypertension, hypercholesterolemia, and coronary artery disease was significantly associated with a microvascular etiology. Despite this, other causes were identified by magnetic resonance imaging or computed tomography scanning in 14% of the patients. These results suggest that neuroimaging may have a role in the initial evaluation of patients with acute ocular mononeuropathies regardless of age.

Commentary

Isolated third, fourth and sixth nerve palsies are a common cause of acute diplopia in neurological practice. The most common etiology is microvascular ischemia of the peripheral portion of the nerves. Microvascular ocular motor nerve ischemia is a presumptive diagnosis in the absence of other neurological signs or symptoms, when no new findings occur during the follow-up period and with spontaneous complete recovery usually within 4 months. It has been controversial whether these patients needed neuroimaging particularly in patients older than age 50. It is widely accepted that acute ocular motor mononeuropathies in persons younger than 50 years of age should be assessed using neuroradiological methods. In the present study, etiologies in 9 patients of 66 who had lesions other than peripheral microvascular ischemia included intracranial neoplasm, brain stem infarct, aneurysm (which was in 1 patient—a pupil sparing third nerve palsy), demyelinating disease, and pituitary apoplexy. The management of these patients would have been delayed if the underlying etiology had not been determined using neuroradiological imaging.

The present investigation also shows that historical data, including the time to maximal diplopic symptoms and vascular risk factors, could not be used with complete confidence to distinguish peripheral microvascular from other etiologies.

It is generally accepted that third nerve palsies, which accompany diabetes, spare the pupil. However, in the present study, microvascular third nerve palsies showed pupillary involvement in 28% of cases, and in 43% of the cases the anisocoria was more than 2 mm. Chou et al note that the 14% of patients who had etiologies other than microvascular would have had an alteration in immediate patient management. They, therefore, recommend neuroimaging in the initial evaluation of adults with acute ocular motor mononeuropathies. This appears to be a reasonable recommendation. — M. Flint Beal

Dr. Beal, Professor and Chairman; Department of Neurology; Cornell University Medical College New York, NY, is Editor of Neurology Alert.