| Affiliation |
(AGL) Chairman, Department of Ophthalmology, The Methodist Hospital, Houston, Texas; Professor of Ophthalmology, Weill Cornell Medicine, New York City, New York; (KS) Class of 2023, Baylor College of Medicine, Houston, Texas |
| Transcript |
So today we're going to talk about Neuromyotonia, and basically it's what the name implies there is going to be increased tone, ‘tonia,' of the muscle, ‘myotonia,' and it's thought to arise from ephaptic transmission from the nerve. ‘Neuromyotonia.' And because we are Neuro-op we are only going to be talking about Ocular Neuromyotonia although obviously Neuromyotonia can be in other places. So, the muscles, ‘myo,' that we are talking about are the extra-ocular muscles. So, if these are the eyes you've got your medial rectus, your lateral rectus, your superior rectus, etc. So, when we have patients that have Neuromyotonia the muscle will fire because of ephaptic transmission from the nerve that will increase the tone of that muscle. So, for example, if we have third nerve-related myotonia the medial rectus muscle might fire spontaneously and then get stuck like that. So, when the muscle fires, so the medial rectus fires it might get stuck like that. It's a muscle spasm like a charley horse in your leg, you get pain, spasm, and instead of the muscle being weak - normally if the medial rectus was weak, we would get exotropia deviation. If the medial rectus is firing too much because it has too much tone, then it'll make esotropia and it'll get stuck like that. So, the eye slowly turns in, gets stuck, and then let's go. Normally, this happens after having radiation therapy. If you've had a seller mass or cavernous sinus lesion and it's been radiated, that radiation therapy damages the nerve. Then, if ephaptic transmission is neuronal crosstalk, the signal in the nerve leaks out of the normal nerve and fires this other nerve by accident. It's got a very characteristic sound to it. The patient will say, ‘I have intermittent double vision." It's usually evoked by gaze in the direction of the spastic muscle, it's a slow movement, and then it slowly releases and it's painful because it's like a charley horse. So, it's not weakness, it's not paresis, it's spasm and increased tone. It's in the muscle, it usually follows radiation therapy but sometimes it's idiopathic or is associated with Graves' disease, or thyroid eye disease. But, usually it's paracellular lesions that have been radiated and it leads to intermittent diplopia that comes on with gaze. So, when we see a slow, tonic muscle movement evoked by gaze associated with pain, Neuromyotonia is what you should be thinking about. Then, you ask them about the radiation therapy. |
