Paresis of cranial nerves III, IV, and VI: clinical manifestation and differential diagnosis.

Successful identification of the cranial nerve and ocular muscle responsible for a subjective complaint of diplopia requires an evaluation of the type and character of the double vision and not infrequently the use of a red glass or Maddox rod, especially in incomplete and subtle cases. An isolated third nerve lesion is most commonly seen with a supraclinoid aneurysm (pupil dilated and fixed), vascular disease (pupil spared), and trauma. Mild frontal head trauma and vascular disease are the most common etiologies associated with an isolated fourth nerve paresis. Tumor, vascular disease and trauma should be prime considerations when a patient presents with an isolated sixth nerve paresis. A child's diagnostic possibilities will differ from the adult: third nerve (congenital), fourth nerve (congenital), and sixth nerve (brainstem glioma, postviral or inflammatory). Finally, myasthenia gravis can readily mask or mimic an isolated or mixed cranial nerve palsy. A Tensilon test is always indicated in unexplained diplopia with ophthalmoplegia and normal pupils.