Tonic ocular tilt reaction simulating a superior oblique palsy: diagnostic confusion with the 3-step test.

BACKGROUND The tonic ocular tilt reaction (OTR) consists of vertical divergence of the eyes (skew deviation), bilateral conjugate ocular torsion, and paradoxical head tilt. The head and superior pole of both eyes are rotated toward the hypotropic eye. OBJECTIVE To describe ocular motility and torsion findings in 5 patients with OTRs that mimicked superior oblique palsies (SOPs). RESULTS In 5 patients, results of the 3-step test suggested an SOP (bilateral in 1 patient); however, no patient had the expected excyclotorsion of the hypertropic eye. Two patients had conjugate ocular torsion (intorsion of the hypertropic eye and extorsion of the hypotropic eye), and 2 patients had only intorsion of the hypertropic eye. All had other neurologic features consistent with more widespread brainstem disease. CONCLUSIONS Vertical ocular deviations that 3-step to an SOP are not always caused by fourth nerve weakness. When a patient with an apparent fourth nerve palsy has ocular torsion that is inconsistent with an SOP, OTR should be suspected, especially if vestibular system or posterior fossa dysfunction coexists. The rules for the 3-step test for an SOP may be fulfilled by damaging the otolithic projections corresponding to projections of the contralateral anterior semicircular canal. Because results of the Bielschowsky head tilt test may be positive in patients with the OTR, the feature distinguishing OTR from an SOP is the direction of torsion. We advocate use of a fourth step-evaluation of ocular torsion-in addition to the standard 3 steps.