Journal of Neuro-Ophthalmology, June 1987, Volume 7, Issue 2

Pseudo-internuclear ophthalmoplegia with downshoot in myasthenia gravis.

Internuclear ophthalmoplegia is characterized by an adduction deficit on lateral gaze with dissociated nystagmus of the abducting eye. It is seen with lesions of the medial longitudinal fasciculus. In myasthenia gravis, extraocular muscle weakness can cause the same oculomotor pattern, which has been referred to as pseudo-internuclear ophthalmoplegia. We report the additional finding of downshoot in the adducting eye in two patients with pseudo-internuclear ophthalmoplegia and positive Tensilon tests.

Journal of Cllllieal Neuro-ophthaimoio;.:y 7(2): 74-76, 1987. Pseudo-internuclear Ophthalmoplegia with Downshoot in Myasthenia Gravis Walter M. Jay, M.D., Sarkis M. Nazarian, M.D., and David W. Underwood, M.D. {. 1987 Raven Press, New York Internuclear ophthalmoplegia is characterized by an ad­duction deficit on lateral gaze with dissociated nys­tagmus of the abducting eye. It is seen with lesions of the medial longitudinal fasciculus. In myasthenia gravis, extraocular muscle weakness can cause the same oculomotor pattern, which has been referred to as pseudo-internuclear ophthalmoplegia. We report the additional finding of downshoot in the adducting eye in two patients with pseudo-internuclear ophthalmoplegia and positive Tensilon tests. Key Words: Myasthenia gravis-Ophthalmoplegia­Pseudo- internuclear ophthalmoplegia. From the Departments of Ophthalmology (W.M.J., D. W.U.) and Neurology (S.M.N.), University of Arkansas for Medical Sciences, and the John L. McClellan Veterans' Hospital, Little Rock, Arkansas. Address correspondence and reprint requests to Walter M. Jav, M.D, Department of Ophthalmology, University of Ar­'''''. 1-. (oJr 1\ledical Sciences, Mail Slot 523, 41(1] W. M'arkham, ,I p :~2():;, USA 74 Internuclear ophthalmoplegia represents a focal central nervous system lesion involving the medial longitudinal fasciculus. On lateral gaze, an adduc­tion deficit is noted, with dissociated nystagmus of the abducting eye. Internuclear ophthalmo­plegia is associated with vascular occlusive disease (unilateral, elderly patients) and multiple sclerosis (bilateral, younger patients). Glaser, in 1966, proposed the term pseudo-in­ternuclear ophthalmoplegia to describe the ocular motility disturbance occurring in myasthenia gravis, which simulates internuclear ophthalmo­plegia (1). He reported three cases of ocular myas­thenia gravis, each with an adduction deficit on lateral gaze with a dissociated nystagmus of the abducting eye. In each case, a Tensilon test was performed, with prompt resolution of the motility disorder. We report herein two cases of ocular my­asthenia gravis presenting with pseudo-internu­clear ophthalmoplegia, with the additional finding of downshoot on attempted adduction. CASE REPORTS Case 1 A 32 year-old-white man came for evaluation of diplopia of 3 weeks duration. He complained that his left eye would not "move in." He also reported musculoskeletal complaints, which had been diag­nosed as fibrositis and treated with Tofranil. On ocular examination, his best corrected visual acuity was 20/20 in both eyes. The pupils were reactive, without afferent pupi1lary defect. The re­sults of biomicroscopy and ophthalmoscopic ex­aminations were normal. On attempted dextrover­sion, the left eye showed decreased adduction with a downshoot on the attempt, and a hori­zontal jerk nystagmus was noted in the abducting PSEUDO-INTERNUCLEAR OPHTHALMOPLEGIA IN MYASTHENIA GRAVIS 75 right eye (Fig. 1). Levoversion was normal. A V­pattern exotropia was noted. The patient was ap­proximately 15 prism diopter exotropic on upgaze and orthotropic on downgaze. On attempted con­vergence, the left eye again demonstrated dimin­ished adduction with a downshoot on the at­tempt. Forced ductions were normal. A Tensilon test showed resolution of the ocular motility dis­turbance, including the downshoot. The remainder of the evaluation revealed nor­mal thyroid function and a small thymic remnant on computed tomography of the mediastinum. Computed tomography of the orbits was normal. The patient was given Mestinon, 60 mg three times per day initially, and the dosage was in­creased to seven times per day, with resolution of his diplopia and improvement of his extraocular movements. Case 2 A 65 year-old-white man had had a 2-month his­tory of double vision. The past medical history was significant for hypertension of 12 year's dura­tion, which was currently being controlled with diuretics. On ocular examination, his best corrected visual acuity was 20/20 in both eyes. The results of pupil­lary examination, biomicroscopy, and ophthalmo­scopic examination were normal. On attempted levoversion, the right eye showed decreased ad­duction with a prominent downshoot, and a small amplitude dissociated nystagmus was apparent in the abducting left eye. An A-pattern esotropia was present. The patient measured -6-8 prism diop­ters esotropic in upgaze and orthotropic in down­gaze. No other duction deficits were noted, A FIG. 1. On right horizontal gaze, light reflex superior to pupillary margin in left eye indicating depression. Tensilon test gave complete resolution of his mo­tility disturbances. The results of further evaluation, including computed tomography of the mediastinum and the orbits, and thyroid functions, were normal. The patient was initially given Mestinon, 60 mg five times per day, with subjective improvement in his diplopia. One week prior to his 3-month follow-up examination, he experienced the onset of ptosis of the left upper lid and bilateral pseudo­internuclear ophthalmoplegia with downshoot in both eyes (Fig. 2). Prednisone, 20 mg daily, was added to his treatment regimen, with resolution of his abnormal eye movements. DISCUSSION Ninety percent of patients with myasthenia gravis eventually have ocular muscle involvement (2). Typically, there will be an acquired ocular mo­tility disturbance, ptosis, and sparing of the pu­pils. The extraocular muscle involvement can vary from an isolated muscle palsy to total external ophthalmoplegia. Medial rectus muscle palsy and upgaze weakness are early signs (3), Pseudo-internuclear ophthalmoplegia with oc­ular myasthenia gravis has been well described (4-6). Other conditions associated with ocular mo­tility disturbances resembling internuclear oph- FiG. 2. On righi and ieft flori'zontal gaze, bilateral pseudo-internuclear ophthalmoplegia with down­shoot. I Clin Neuro-ophthalmol, Vol. 7, No.2, 1987 76 W. M. JAY ET AL. thalmoplegia include Guillain-Barre polyneuritis (7,8), Miller-Fisher's variant (acute idiopathic polyneuritis) (9), and surgical paresis of the medial rectus muscle (10). Penicillamine may cause myasthenic weakness with pseudo-internuclear ophthalmoplegia (11). In this report, we describe two patients with pseudo-internuclear ophthalmoplegia with the ad­ditional finding of downshoot on adduction. A re­strictive phenomenon such as that seen in Grave's ophthalmopathy could be considered. In our two patients, forced ductions, orbital computed to­mography, and thyroid function studies showed normal results. The downshoot was similar to that frequently seen with Duane's retraction syndrome, which is characterized by decreased abduction with retrac­tion on attempted adduction. A tethering or slip­ping effect of the lateral rectus muscle is believed to be responsible for this downshoot (12). Neither of our patients had abduction deficits or retraction on adduction. There are dissimilarities in the appearance of the downshoot in our two cases. In Case 1, adduc­tion was minimal and a V-pattern exotropia was present. In Case 2, adduction was only moder­ately impaired and an A-pattern esotropia was evi­dent. The findings in Case 2 are compatible with bilateral superior oblique overaction, presumably secondary to inferior oblique weakness caused by the underlying myasthenia. In Case 1, however, it is difficult to hypothesize a superior oblique over­action. The downshoot occurred in only slight ad­duction, and a V-pattern exotropia was present. In Case 1, a superior rectus muscle weakness with secondary inferior rectus overaction may have been the cause. If this was so, however, it is not I Clin Neuro-ophthallllol, \lvl. ,:\/0. _, 19S7 clear why the downshoot would occur in adduc­tion, rather than abduction. One can postulate an attempt by the vertical recti to aid in adduction by their tertiary action, causing depression of the eye due to superior rectus weakness. At any rate, the clinical picture on lateral gaze of an adduction def­icit with a downshoot accompanied by nystagmus in the abducting eye should alert the clinician to the possibility of myasthenia gravis. REFERENCES L Glaser JS. Myasthenic pseudo-internuclear ophthalmo­plegia, Arch Ophthalmol 1966;75:363-6. 2. Orachman OM. Myasthenia gravis. N Engl J Med 1978; 298:136-42.186-93. 3. Glaser JS. Neuro-ophthalmology. Hagerstown: Harper and Row, 1978:270. 4. Lyon LW, Van Allen MW. Orbicularis oculi reflex. Arch OphthalmoI1972;87:148-54. 5. Acers TE. Ocular myasthenia gravis mimicking pseudoin­ternuclear ophthalmoplegia and variable esotropia. Am J OphthalmoI1979;88:319-21. 6. Spooner JW, Baloh RW. Eye movement fatigue in myas­thenia gravis. Neurology 1979;29:29-33. 7. Diamond S, Schear HE, Leeds MF. Pseudo-internuclear oculomotor ophthalmoplegia secondary to Guillain-Barre polyneuronitis simulating myasthenia gravis in an air transport pilot. Aviat Space Environ Med 1975;46:204-7. 8. Atwal AJ, Smith BH, Dickenson ES. Pseudo-internuclear ophthalmoplegia in polyneuritis [Letter]. Arch Neuro11976; 33:457. 9. Swick HM. Pseudointernuclear ophthalmoplegia in acute idiopathic polyneuritis (Fisher's syndrome). Am J Oph­thalmoI1974; 77:725-8. 10. von Noorden GK, Tredici TO, Ruttum M. Pseudo-internu­clear ophthalmoplegia after surgical paresis of the medial rectus muscle. Am JOphthalmoI1984;98:602-8. 11. George J, Spokes EG. Myasthenic pseudo-internuclear ophthalmoplegia due to penicillamine [Letter]. J Neural Neurosurg Psychiatry 1984;47:1044. 12. Rogers GL, Bremer OL. Surgical treatment of the upshoot and downshoot in Duane's retraction syndrome. Ophthal­mology 1984;91:1380-3.