| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (BL) Class of 2022, Baylor College of Medicine, Houston, Texas |
| Description |
Summary: • Clinical symptoms o Vertical oscillation of eyes o Vertical oscillation of palate • Pathophysiology o The brainstem is composed of the Guillain-Mollaret triangle -Comprised of dentate nucleus in cerebellum, inferior olivary nucleus in medulla, and the red nucleus in midbrain -Any lesion inside of the triangle disinhibits the connections to the inferior olive, leading to eventual hypertrophy -Hypertrophy leads to activation of cranial nerve fibers in the inferior olive, causing the palatal movement o Causative lesion is often a rostral lesion in the pons, such as a stroke or hemorrhage • Diagnosis o Patient will typically present initially only with ocular findings because it takes time for the hypertrophy to occur o Months later, will have patient present with palatal symptoms and will need to image Guillain-Mollaret triangle in full o On imaging of medulla, will see T2 change and increased signal from the inferior olivary nucleus |
| Transcript |
Today we're going to be talking about oculopalatal myoclonus and it's called that because the eye is going up and down vertically, the palate is also moving up and down, and it's myoclonus. It looks like this, so vertically, where the eye will be going up and down-so it's not like downbeat, which has a fast phase down or upbeat which has a fast phase up and nystagmus. It is a pendular vertical oscillation. It's often very small in its amplitude. So, if we see a vertical pendular oscillation of the eyes-ocular-then we want to have them open their mouth and look at the palate. The dangly thing in the roof of your mouth, the uvula, will be going up and down like this. So, if the eyes are going up and down and the palate is going up and down-that is oculopalatal myoclonus. This oculopalatal myoclonus occurs because there's a lesion in the brainstem inside of the Guillain-Mollaret triangle. The Guillain-Mollaret triangle is composed of the dentate nucleus in the cerebellum, the inferior olive in the medulla, and the red nucleus. So, if you have a lesion involving the red nucleus, the inferior olive, or the dentate (in the cerebellum), any lesion inside of that triangle-called the Guillain-Mollaret triangle-will disinhibit the connections to the olive. When that happens, the lower cranial nerve, inferior olivary fibers in the medulla will cause the palate to move, because it's been disinhibited. So, when you inhibit the inhibitory fiber it unleashes the palate movement from the lower cranial nerve involved in the medulla, which is the inferior olive. The ocular part occurs obviously from the upper brainstem portion, the red nucleus, midbrain, and cerebellar control fibers in the dentate nucleus, cerebellum. The interesting thing about this is there's normally some lesion that starts off rostrally, like in the pons, that actually disconnects the descending fiber to the olive. So, it's a delayed effect. It's delayed. So, the patient has a hemorrhage for example in the pons or a stroke in the pons, and then months later, their eyes start to move (the ocular) and then the palate starts to move, because it takes time for the inferior olivary hypertrophy to occur from the disinhibition caused by the initial pontine lesion. The reason it's important is because if you repeat the MRI scan on this patient-who has a new finding, oculopalatal myoclonus-the MRI only shows the same lesion is actually smaller. But the key differentiating radiographic feature that we're going to be looking for is increase in the size of the inferior olive and that's in the medulla, way far away from the eye movement abnormality. So, in summary, in every patient who has a pendular vertical nystagmus, ocular, we have to look at their palate. If we see oculopalatal myoclonus, both the eyes are moving up and down and the palate is moving up and down, then we have to image the patient, looking for a lesion in the Guillain-Mollaret triangle-the dentate nucleus in the cerebellum, the red nucleus, and the inferior olive. Over time, the inhibition of the inhibitory fiber leads to the palatal movement and a radiographic finding of T2 change or increase signal or hypertrophy of the inferior olive in the medulla, and it's a delayed effect after having some rostral lesion, usually a hemorrhage in the pons. |
