||Lesions of which of the following neuro-anatomic structures could result in the clinical findings shown? A. Right medulla B. Right interstitial nucleus of Cajal C. Right medial longitudinal fasciculus D. Left trochlear nerve E. Right caudal midbrain A. Correct. This patient presents with elements of a rightward ocular tilt reaction. He has features of the ocular tilt reaction (OTR) including: 1) ocular counterroll with top poles toward the right ear (i.e., excycloduction OD and incycloduction OS), 2) a right head tilt, and 3) a skew deviation (not seen in the video) with left hypertropia. His perception of earth vertical or subjective visual vertical (SVV) was also tilted to the right (demonstrated in the clinic using the bucket test1), which is thought to be a perceptual consequence of the OTR. The OTR is caused by lesions along the utricle-ocular motor pathways, and is much more commonly related to central rather than peripheral pathology. From the utricle (within the labyrinth), these graviceptive signals traverse the vestibular nerve before synapsing at the vestibular nucleus, then decussate at the level of the pontomedullary junction to ascend contralaterally with the medial longitudinal fasciculus (MLF), where they are relayed to the interstitial nucleus of Cajal. Lesions of the utricle-ocular motor pathway caudal to the decussation cause an ipsiversive OTR (e.g., right head tilt and rightward ocular counterroll with a right lateral medullary stroke) while lesions rostral to the decussation cause a contraversive OTR (e.g., right head tilt and rightward ocular counterroll with a left MLF lesion). B. Incorrect. Lesions of the interstitial nucleus of Cajal (INC) can result in deficits of vertical gaze holding, spontaneous torsional nystagmus (top poles beating ipsilesional) along with the ocular tilt reaction. However, a lesion of the right INC would cause a contraversive (leftward) OTR, which is opposite of the patient shown in the video. C. Incorrect. MLF lesions often cause a complete or partial OTR acutely, which then rapidly improves. Internuclear ophthalmoplegia (INO) is the most typical associated ocular motor finding, and the INO will be ipsilateral to the hypertropic eye. Again, since the utricle-ocular motor fibers that traverse the MLF are rostral to their decussation, an OTR will be contraversive - e.g., a right MLF lesion (like a right INC lesion) will cause a contraversive (leftward) OTR. D. Incorrect. Although a left trochlear or 4th nerve palsy will cause a compensatory rightward head tilt, there should be excycloduction (not incycloduction as in the video) in the hypertropic eye. A 4th nerve palsy also wouldn't cause a significant SVV tilt in the direction of the head tilt. E. Incorrect. If the utricle-ocular motor pathways were affected in the right midbrain on their way to the right INC, the OTR would be contraversive. If there was damage to the nucleus or fascicle of the 4th nerve within the right caudal midbrain, clinically this would present as a left 4th nerve (often associated with one or more of the following ipsilesional findings: right INO, right Horner's, right hemi-ataxia or an afferent pupillary defect without loss of acuity, color or field), as the left 4th nerve originates in the right midbrain and crosses to the left side. A left 4th would be incorrect (see D.). Summary: This is a 55-year-old patient who had an ocular tilt reaction (right head tilt, rightward ocular counterroll, skew deviation with left hypertropia, rightward SVV tilt) in addition to imbalance, frequent square wave jerks, myoclonic jerks involving the arms and legs, and a CSF protein level > 90 (with an otherwise bland profile), with symptoms beginning several months prior to presentation. Work-up for paraneoplastic etiologies, Creutzfeldt-Jakob disease (CJD), and inflammatory/infectious conditions is ongoing. 1. Zwergal A, Rettinger N, Frenzel C, Dieterich M, Brandt T, Strupp M. A bucket of static vestibular function. Neurology 2009;72:1689-1692.