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Re: nystagmus

Posted By CCF MD mdf on June 05, 1998 at 09:07:04:

In Reply to: nystagmus posted by Kathleen on June 03, 1998 at 06:48:53:

I am being treated for Lyme disease with central nervous system
involvement.  I have had some trouble for months with decreased visual
contrast and brightness but with no apparent loss of visual acuity or
color vision.  I have also noticed a problem with reading, (can't seem
to quite focus on the words, or something, but without blurriness)
particularly when I am tired or have been reading for awhile.
I had an MRI (head and C-spine) done on Monday and saw my physician the
same day.  When I related to him that I have difficulty focusing on
objects straight on, he checked my eye movements (follow an object with
eyes only) and found that I have a horizontal nystagmus of the right eye
at a point nearly straight ahead.  This could certainly explain the
difficulty in reading.  I had never been found to have nystagmus before,
and my doctor will probably refer me to a neurologist pending results of
the MRI.
What are the implications of nystagmus, particularly in association with
the "dullness" in vision?  I have no symptoms of dizziness at all.  I
know that is a very vague question, but I want to know anything you can
tell me about it, and I am not sure just what to ask.  Is it a sign of
cranial nerve dysfunction or something going on in the brain?  Is this
type of nystagmus likely to ever go away on its own, or would it be more
likely to progress?  
I have several other symptoms, many of which seem to be neurological,
including weakness of the arm muscles, particularly of the right arm,
and recently a subjective feeling of tremor in the arms and legs on
"stressing" the muscles (e.g. leaning over to pick up laundry, etc.).  
The tremor-feeling, the visual difficulties, and the fatigue have not
responded to IV antibiotics, even though other symptoms have.
Thank you for your time.
If you have not had an evaluation by a neurologist before, you should probably reconsider the whole diagnosis of Lyme disease with CNS involvement. It may, in fact, be what you have, but it still is best to be sure no assumptions have been made and all the pieces fit together in a way that makes sense.
Re: Nystagmus. I'll give you a thumbnail sketch of what it's all about, and perhaps you'll be prepared to understand the implications of whatever your neurologist tells you as a result.
Nystagmus is a type of conjugate eye movement (that is, both eyes in synchrony) in which there is a slow drift to one side (horizontal or vertical, or even rotatory) followed by a fast phase in the opposite side. The direction of the nystagmus is named for the fast component (for example, up-beating or left-beating).
Nystagmus can be normal. For example, if you are a passenger in a car on the highway and you look out the window at phone poles, your eyes will fix on one pole, follow it ("pursuit movement") until some point at which your eyes flick forward to target the next pole. This can be simulated in the doctor's office with a drum (like a barber pole) with alternating colors. This is called optokinetic nystagmus and is normal.
Another normal type of nystagmus is "post-rotatory" nystagmus. Whirl around on a swivel chair for a few rotations, then stop. An observer will see that your eyes are doing just that.
The neurologic mechanisms differ. The actual circuitry driving the eye movements are in the brain stem (groups of cells which contribute fibers to cranial nerves 3, 4, and 6). But that's just the motor, if you imagine a car analogy. Each of the two examples above has a different "driver." The optokinetic nystagmus is driven by visual stimuli processed in visual cortex, whose signals then are sent to the brainstem. The second example is driven by the vestibular system, which is connected to the inner ear and circuitry in the brainstem.
So you can see the first order of business is to determine whether nystagmus is normal or abnormal. I would suppose that spontaneous nystagmus in the neutral gaze position is probably abnormal. Next, one must figure out what circuitry is involved: typically we make the distinction between central (brainstem) and peripheral (inner ear). Your neurologist will ask questions and direct the physical (neurologic) exam to figure this out. Often, I send people for vestibular function tests, which are performed by ENT specialists.
Once the normal/abnormal question is answered, and when the localization is known, then it is appropriate to try to define the process which caused the abnormality. Nystagmus has too many causes to list here. Some are benign, others signal problems. I suppose it's possible that Lyme disease can be responsible, but as above, be sure no one jumps to any assumptions. If that's the conclusion that your doctor reaches, it's best if you have confidence that he/she approached the question from ground zero.
I hope this answers enough of your question to be helpful. As you might imagine, this can be more complicated than I have outlined here. This information is for your general medical education only. Specific comment regarding your diagnosis, treatment options, and prognosis must come from your doctor after appropriate evaluation. CCF MD mdf.

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