Cause and prognosis of neurologically isolated third, fourth, or sixth cranial nerve dysfunction in cases of oculomotor palsy

Purpose: To determine the cause and prognosis of neurologically isolated third, fourth, or sixth cranial nerve dysfunction in cases of oculomotor palsy, and to determine the best imaging methods to make a correct diagnosis. Methods: The medical records of 221 consecutive patients with oculomotor palsy caused by neurologically isolated cranial nerve dysfunction were reviewed. There were 63 cases of third, 41 of fourth, and 117 of sixth cranial nerve dysfunction. The patients were examined at the Neuro-ophthalmology Clinic of Kyoto University Hospital between 1993 and 2001. Results: Vascular disorders accounted for 34.9% of the third nerve dysfunction, and 90% of these recovered completely in 6 months. Ninety percent of the patients with an isolated third nerve dysfunction that was caused by an aneurysm also had anisocoria, and 68% of the patients with a third nerve dysfunction caused by a vascular disorder had anisocoria. In all of the vascular cases with anisocoria, the difference in the pupillary diameter was < 1.0 mm. The presence of ptosis did not play an important role in making a diagnosis of third nerve dysfunction. Ninety percent of the patients with fourth nerve dysfunction and 60% of the patients with sixth nerve dysfunction recovered within 9 months. Conclusions: The age of the patient, signs of an improvement, and associated alterations are important diagnostic markers to determine the best type of imaging methods for evaluating neurologically isolated third, fourth, and sixth cranial nerve dysfunction.