Comparing Hypertropia in Upgaze and Downgaze Distinguishes Congenital From Acquired Fourth Nerve Palsies

Background: Isolated fourth nerve palsies are commonly caused by decompensation of a congenitally dysfunctional superior oblique muscle (“decompensated congenital palsies”). Distinguishing such palsies at initial presentation from palsies caused by presumed microvascular ischemia (“ischemic palsies”) has value for patient reassurance and in forestalling ancillary testing. Abnormally large vertical fusional amplitudes traditionally have been used to identify decompensated congenital palsies, but that may not be a reliable distinguishing feature. This study was undertaken to determine if the amount of hypertropia in upgaze and downgaze might be a more efficient separator. We also studied traumatic and tumorous fourth nerve palsies to see if they could be distinguished from decompensated congenital palsies by using this hypertropia comparison. Methods: Retrospective review of case records of patients diagnosed with isolated fourth nerve palsies at the University of Michigan Neuro-Ophthalmology Clinics over the past 15 years. We recorded the age, gender, vascular risk factors, duration of follow-up, cause, side of palsy, and alignment measurements in all patients. Results: Inclusion criteria were met by 118 patients. Hypertropia was equal or greater in upgaze than downgaze in 50 of the 58 decompensated congenital palsies (86%) in whom those data were recorded. Hypertropia was never greatest in upgaze in the 15 patients with traumatic palsies. Vertical fusional amplitudes were increased in only 15 of 27 patients (56%) with decompensated palsies in whom those data were recorded. Torsional misalignment on double Maddox rod testing was present in 16 (94%), 13 (87%), and 3 (100%) patients with ischemic, traumatic, and tumorous palsies, but also in 19 patients (54%) with decompensated congenital palsies in whom those data were recorded. Conclusions: Hypertropia greater in upgaze than downgaze or equal in upgaze and downgaze was an efficient separator of congenital from ischemic and tumorous fourth nerve palsies, being characteristic of patients with decompensated congenital palsies and never present in patients with ischemic, traumatic, or tumorous palsies. Vertical fusional amplitudes and torsional misalignment did not effectively differentiate between the patient groups. Comparing the hypertropia in upgaze and downgaze improved differential diagnosis and reduces the potential for unnecessary ancillary tests.