Downbeat_Nystagmus

This 58 year old engineer was referred by his neurologist for evaluation of periodic episodes of difficulty focusing and blurred vision for 8 years. In 1981 whilst sightseeing in Newport, he became acutely aware of difficulty focusing and blurry vision. The symptoms lasted for twenty minutes and then cleared. He had no diplopia, vertigo or headache. Over the next several years, he continued to experience episodic visual symptoms which increased both in frequency and duration. In 1988 he recognized that his blurred vision was due to vertical movement of images, which he described "like a television that has lost its vertical hold and the visual world is rolling over vertically in front of me". In 1989, on referral to the Neurovisual Unit oscillopsia was recurring every day, frequently first thing in the morning. It was noteworthy that he had no blurred vision lying in bed or when sitting still. But, oscillopsia was provoked by rapid head turning when reversing his car, or moving his head rapidly whilst driving. Slow movements of his head did not provoke oscillopsia. Past history: Mild amblyopia in the right eye since childhood. In 1969, right myringotomy to drain fluid from the middle ear. Mild bilateral nerve deafness, no tinnitus. Migraine as a young man. No history of head trauma or drug or alcohol abuse. Family history: Negative for neurological disease. Medications: Anti-hypertensive medications only. Neuro-ophthalmological examination: Visual acuity OD: 20/25, reads J1 OS: 20/20, J1+ Stereopsis impaired 3/9 circles Visual fields, pupils, fundus examination normal. Ocular motility: No nystagmus in primary gaze Large amplitude slow downbeat nystagmus on gaze right and left Full upgaze no nystagmus Full downgaze with small amplitude downbeat nystagmus Normal convergence accentuating downbeat nystagmus Smooth horizontal and upgaze pursuit Saccadic pursuit on downgaze Absent OKN stripes down Normal OKN stripes up Neurological examination: Normal No ataxia, normal gait. Brain MRI with contrast ruled out Arnold Chiari malformation. The study was normal ELECTRONYSTAGMOGRAM 1. Spontaneous and gaze-evoked nystagmus No nystagmus with eyes open in the light Left beating nystagmus on 30° left gaze with eyes closed. Slow phase velocity 2°/sec. With the head tilted back approximately 60° and the patient therefore looking down, with eyes closed and eyes in the midline and to the left, there was a rotary nystagmus consisting of down and left components. With the head tilted back, eyes closed and to the right, there is a downbeating nystagmus. 2. Saccades - Normal 3. Pursuit (tracking): 0.2 Hertz: Sinusoidal, above is for horizontal pursuit Vertical pursuit of a finger reveals smooth pursuit of upward movements and saccadic pursuit of down movements. 0.4 Hertz: Sinusoidal. Horizontal pursuit only. 4. Optokinetic nystagmus - Only vertical OKN tested. Upward stimulus movement resulted in a brisk downbeating nystagmus. Downward stimulus movement resulted in no nystagmus. No slow or fast eye movements noted. 5. Positional testing: a. Hallpike/Eyes open in the light. Left beating nystagmus in the left ear down position with a slow phase velocity of 4°/sec., latency, a duration of 66 sec. and no fatiguing on repetition. b. Static/Eyes open in the dark Rotary nystagmus consisting of left and downbeating components seen in the head and body straight (from head and body right position) and in the head and body left position. Horizontal slow phase velocity of 1-5°/sec. Rotary nystagmus consisting of right and downbeating components seen with the head to the right and with the head and body right. Horizontal slow phase velocity of 3°/sec. Left beating nystagmus seen in several supine positions and with the head left. Slow phase velocity 2-4°/sec. All nystagmus was transient. No associated dizziness. c.Static/Eyes closed Transient left beating nystagmus with the head turned to the left. also with the head straight after left. Slow phase velocity 4-7°/sec. 6. Calorics-Stimulation of each ear with 27 and 44° (C) water produced symmetrical and appropriate nystagmus with good fixation suppression. The dizziness provoked by caloric stimulation was different than the patient's symptoms. SINUSOIDAL VERTICAL AXIS ROTATION (Seven frequencies of rotation from 0.01 to 1.0 Hz, 50° per second peak velocity) 1. Gains - within normal limits 2. Phase leads - within normal limits 3. Symmetry - within normal limits 4. Rotational summary - normal rotational summary. 5. Gain and phase lead points within normal limits 6. Responses were symmetrical VISUAL VESTIBULAR INTERACTION 1. VOR - Gain was within normal limits 2. OKN - Gain within normal limits 3. V VOR - Gain within normal limits 4. FIX - Gain was above normal limits 0.1 Summary: Abnormal, consistent with a brainstem or cerebellar lesion because of poor fixation suppression of rotation induced nystagmus. Fixation suppression index was above normal limits. POSTUROGRAPHY Sensory organization and movement coordination All tests normal. Movement coordination All tests normal. Impression: Abnormal electronystagmogram consistent with bilateral labyrinthine, bilateral 8th nerve or brainstem dysfunction because of left and right beating positional nystagmus and some left beating spontaneous gaze nystagmus with eyes closed. Abnormal visual-vestibular interaction consistent with a pontine brainstem or cerebellar lesion. Diagnosis: Idiopathic Downbeat Nystagmus Medications: Three drugs were tested in turn, Baclofen, Meclizine, and Clonazepam, each failed to suppress his oscillopsia. Consultant Opinions: For additional advice on how to treat this patient, I consulted a number of highly experienced colleagues by sending them documentation of the investigations and a video of the patient's eye movements. David Zee, The Johns Hopkins Hospital, Baltimore, MD, raised the possibility that the patient might have a degenerative disorder because of the progressive history over 8 years. David recommended a trial of Clonazepam 2 mg. tablets starting 1 tablet daily increasing to 2 tablets daily after two weeks and increasing to 3 tablets daily after a further two weeks for a three month trial. This medication failed to help. Myles Behrens, Columbia Presbyterian Hospital, New York City, NY, suggested the etiology was possibly degenerative (including alcohol) ischemic (hypertension) or conceivably demyelinating disease even though MS is not among the cases in the large series published by Halmagyi et al (5). Myles drew my attention to a report by Currie et al (4). Single vision readers had benefited from (maximal) base down ground in prism glasses. Simmons Lessell, Massachusetts Eye and Ear Infirmary, Boston, MA, examined the patient and recommended referral to a strabismus specialist, Craig McKeown. Craig McKeown attempted a trial of bilateral hand held base down 20 diopter prisms in the office but was unable to clearly establish that this improved the patient's oscillopsia. Had the patient experienced some symptomatic relief with this procedure then he might have been a candidate for bilateral symmetrical vertical rectus muscle surgery in an attempt to swing his eyes to downgaze. Robert Reinecke, Wills Eye Hospital, was consulted regarding strabismus surgery. Bob wrote in his letter to me "It has not been too infrequent in my experience to not be able to find any etiology for this. I think no etiology is found in about 15 to 20% of the cases. The question, of course, is the treatment that is most effective. I have been particularly encouraged by the surgical treatment of several patients. The procedure is the same as one would use for horizontal null point in the Kestenbaum-type procedure. In your patient, one would try to move the straight ahead position where he is quite stable down to the reading position and give the up position of gaze where he is also quite stable sort of straight ahead. The easiest way to think of this is to think of the eye in the up position, removing the vertical recti, turning the eye down, and resuturing the muscles to the globe. To achieve this one has to do large recessions of the superior recti muscles and somewhat smaller but still fairly large resections of the inferior recti and warn the patient of the possibility of some vertical asymmetry after surgery." Treatment I shared all the opinions with the patient and he elected a trial of Klonopin 0.5 mg. tablets one daily and he stayed on Klonopin permanently. He was lost to follow up after he moved to Sarasota, Florida in 1981. See also: http://content.lib.utah.edu/cdm/ref/collection/ehsl-shw/id/6