| Identifier |
uhthoff_phenomenon_lee_novel |
| Title |
Uhthoff Phenomenon |
| Creator |
Andrew G. Lee, MD; Gary Zhang |
| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (GZ) Class of 2024, Baylor College of Medicine, Houston, Texas |
| Subject |
Multiple Sclerosis; Vision Loss |
| Description |
Summary: • Uhthoff phenomenon overview: o Symptoms include vision loss caused by heat, exertion, or exercise o Not necessarily just poor vision, can also lead to numbness or weakness o Seen in people with multiple sclerosis (MS) • Pathophysiology o Seen in people with MS since they rely on regular conduction over saltatory conduction, which is less efficient o Caused by conduction block, as sodium channels are closed and potassium channels opened with increasing core body temperature • Treatment o 4-amino pyridine (4-AP) is a selective potassium channel blocker that can help treat the Uhthoff phenomenon o Countermeasures to reduce body temperature are also used, such as avoiding heat, hot baths, saunas, etc. |
| Transcript |
So today we're going to be talking about the Uhthoff phenomenon and Uhthoff phenomenon is a very interesting complaint that you need to know about and the patient will say my vision is worse with heat or exertion or exercise. It's thought to be a temperature dependent thing -it doesn't have to be the vision, it could be numbness or weakness or any symptom -it's a symptom that we see in multiple sclerosis from demyelination. So as you know, in a normal nerve, the conduction of myelinated nerve passes through these nodes, and the nodes are called the nodes of Ranvier and these nodes allow for the impulse to jump and that jumping we call saltatory. So this is saltatory conduction in a normal myelinated nerve; however, if you damage the myelin, then you can't take advantage of the jumping with the nodes and so then you're going to have to rely on regular conduction and that's going to be slow. In addition, there might be a conduction block and so you might lose your vision. So in patients who have optic neuritis, they can either have decreased vision or decreased visual field or color vision and they might say the vision is worse with the heat, and that is the Uhthoff phenomenon. So in patients who have this Uhthoff phenomenon, it is thought that there's been depolarization and an effect on the action potential. That action potential is dependent on electrolyte channels in the membrane and one of those is sodium and the other is potassium; as you know these are both integrally involved in the generation of the action potential and so in a normal patient who has normal conduction, the sodium channel will open and then close and we want to maintain a balance between the efflux and influx of these electrolytes. And so in patients who have a elevation in their core body temperature, this might cause this channel to open and this might cause this channel to open or the reverse. And so when we have a conduction block, they have closure of the sodium channel. If we have opening of the potassium channel, those are the things that are going to be associated with a change in the conduction pathway. So in the treatment of the Uhthoff phenomenon, we have a blocker that can block the opening of the potassium channel and that is 4-amino pyridine, which is a selective potassium channel blocker, which we can use to treat the Uhthoff phenomenon. In addition, the change in the core temperature can open or close the sodium channel; and so efflux and opening of the potassium channel or closing of the sodium channel are both integrally involved in producing the symptom that we call the Uhthoff phenomenon. Vision loss and optic neuritis worsen with heat, and so if you live in a hot place like Houston, Texas, we want to do the countermeasures to reduce that temperature dependent symptom by having cooling and avoiding going outside when it's too hot and over getting overheated and wearing something around your head to keep it cool and ice pack and avoiding the sauna and the hot tub or even a very hot shower or even a hot heat hairdryer on your eye. So you need to know that this very strange symptom- vision loss worse with heat- it's got a name called the Uhthoff phenomenon, it is disruption of the saltatory conduction along the nodes of Ranvier created by de-myelination, and mechanistically it might be from closing and opening the sodium channel, closing and opening the potassium channel, and that we have a pharmacologic remedy to close the potassium channel but also to open and close, with core body temperature changes, the sodium channel. |
| Date |
2021-04 |
| Language |
eng |
| Format |
video/mp4 |
| Type |
Image/MovingImage |
| Collection |
Neuro-Ophthalmology Virtual Education Library: Andrew G. Lee Collection: https://novel.utah.edu/Lee/ |
| Publisher |
North American Neuro-Ophthalmology Society |
| Holding Institution |
Spencer S. Eccles Health Sciences Library, University of Utah |
| Rights Management |
Copyright 2019. For further information regarding the rights to this collection, please visit: https://NOVEL.utah.edu/about/copyright |
| ARK |
ark:/87278/s63v5drs |
| Setname |
ehsl_novel_lee |
| ID |
1680634 |
| Reference URL |
https://collections.lib.utah.edu/ark:/87278/s63v5drs |
