Etiologies of Fourth Cranial Nerve Palsies: a Population-based Study

Abstract

Purpose: : Previous studies of 4^th nerve palsy have been institution based and therefore may suffer from referral bias. We conducted a population-based study to determine the relative frequency of causes of isolated 4^th nerve palsy, using strict definitions for presumed congenital, hypertension, and diabetes mellitus.

Methods: : The resources of a population-based diagnostic database were used to identify all cases of isolated 4^th nerve palsy (including bilateral) in a single county, located in the Upper Midwest of the USA, over a 15-year period. The entire medical record of each case was reviewed to determine the most likely etiology. Decompensated congenital 4^th nerve palsy was defined as at least one of the following: infantile onset, pre-existing vertical phoria, large fusional amplitudes, or long-standing head tilt. Hypertension was defined using Joint National Committee (JNC7) criteria and Diabetes Mellitus using ADA criteria.

Results: : We identified 76 cases of isolated 4^th nerve palsy over the 15-year period. 96% were unilateral and 4% were bilateral. The most common causes were presumed congenital (45%), hypertension (18%), and trauma (18%). The other causes were hypertension with diabetes (7%), post-neurosurgery (3%), diabetes alone (1%), known intracranial neoplasm (1%) and undetermined (7%). Overall, the peak decade of life for presentation was the 4^th decade. For presumed congenital cases, the peak decade for presentation was the 4^th decade (not childhood), for trauma the peak decade was the 3^rd and for hypertension the 7^th and 8^th. There were no cases where an isolated 4^th nerve palsy was the presenting sign of a neoplasm (95% CI 0% to 4.7%)

Conclusions: : Using population-based methodology, isolated 4^th nerve palsy most commonly presents in adulthood, with most common etiologies of presumed congenital, hypertension and trauma. Although the most common etiology was presumed congenital, even these cases present more commonly in adulthood than childhood, most likely due to late decompensation.

Keywords: strabismus: etiology • neuro-ophthalmology: diagnosis