Daniel R. Gold, DO, Departments of Neurology, Ophthalmology, Neurosurgery, Otolaryngology - Head & Neck Surgery, The Johns Hopkins School of Medicine
This is a 75-yo-woman presenting with a gait disorder. Two years prior, she suffered a cerebellar hemorrhage. On examination, there were typical cerebellar ocular motor signs including gaze-evoked nystagmus, choppy smooth pursuit and VOR suppression, and saccadic dysmetria. There was also an alternating hypertropia also known as an alternating skew deviation. When there is unilateral damage to the utricle-ocular motor pathways, a skew deviation is the result. The ocular tilt reaction - a combination of skew deviation, ocular counterroll, and head tilt - may be seen in full, or only 1-2 features may be present (seen with brainstem>cerebellar injury). When bilateral, symmetric utricle-ocular motor pathway damage is suffered, the result is usually an alternating skew deviation - i.e., right hypertropia in right gaze and left hypertropia in left gaze. Because this is often accompanied by gaze-evoked nystagmus, accurate measurement of the alternating hypertropia can be difficult. Maddox rod testing is perhaps an easier (albeit subjective) way to look for an alternating skew deviation. Finally, oculopalatal tremor is a common occurrence following a brainstem or cerebellar hemorrhage (less commonly ischemia), and this may be seen months to years later. Mollaret's triangle consists of the following connections: red nucleus to ipsilateral inferior olivary nucleus via central tegmental tract; inferior olivary nucleus to contralateral Purkinje cells of the cerebellar cortex via climbing fibers in the inferior cerebellar peduncle; Purkinje cells to ipsilateral dentate nucleus (cerebellum); dentate nucleus to contralateral red nucleus via superior cerebellar peduncle. Disruption anywhere within this triangle can result in degenerative hypertrophy of the inferior olivary nucleus (hyperintense inferior olive(s) on T2 of FLAIR), and formation of abnormal coupling between cell bodies of neurons and synchronous discharges resulting in synchronous vertical pendular nystagmus (often with a torsional component) and ocular palatal myoclonus or tremor. Occasionally, palatal tremor is in isolation or nystagmus is in isolation depending on which portions of the inferior olivary nucleus are involved or spared. In this patient's case, there was no pendular nystagmus. Palatal tremor should be sought in any patient who suffered a posterior fossa injury and complains of persistent or worsening dizziness or imbalance. The palate should be viewed at rest. Number of Videos and legend for each: 1, Patient who experienced cerebellar hemorrhage years prior demonstrating gaze-evoked nystagmus, alternating skew deviation and palatal tremor.
Spencer S. Eccles Health Sciences Library, University of Utah