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44 year-old man with double vision
Digital Journal of Ophthalmology 2006
Volume 12, Number 4
December 3, 2006
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Joseph Rizzo, M.D. | Harvard Medical School/Massachusetts Eye and Ear Infirmary
Corey Westerfeld, M.D. | Harvard Medical School/Massachusetts Eye and Ear Infirmary
Differential Diagnosis
Fourth cranial nerve palsies must first be distinguished from other causes of vertical diplopia. These include oculomotor palsy, skew deviation, myasthenia gravis, and Graves' ophthalmopathy. These patients typically have other clinical findings that help differentiate them from isolated fourth nerve palsies. Furthermore, in time, these patients often develop other findings that unmask the diagnosis.(1) The differential diagnosis of a fourth nerve palsy can be subdivided into congenital versus acquired. Congenital fourth nerve palsies are identified in several ways. First, the patient will often have very high vertical fusional amplitudes. Normal vertical fusional amplitudes are in the range of 1-3 prism diopters. Patients with a congenital fourth nerve palsy can often fuse 10-15 prism diopters. Also, old pictures can be examined to determine whether or not there has been a long-standing head tilt since childhood. This would give more evidence to suggest that the fourth nerve palsy was congenital. When a cause can be identified, the most common etiology of an acquired fourth nerve palsy is trauma. Another common etiology is microvascular or ischemic, often in the setting of diabetes or hypertension.(2) Other etiologies include compressive lesions such as tumors or aneurysms, increased intracranial pressure, intrinsic neoplasms of the fourth nerve, and, very rarely, giant cell arteritis.