Journal of Neuro-Ophthalmology, September 2001, Volume 21, Issue 3

Ocular Myasthenia Mimicking a One-and-a-Half Syndrome

A 52-year-old patient developed an eye movement disorder first resembling a left internuclear ophthalmoplegia and subsequently a "one-and-a-half syndrome" as the presenting symptoms of ocular myasthenia gravis. No accompanying myasthenic features were present except for the fluctuation in the amplitude of dissociated nystagmus. This patient shows that an oculomotor disorder considered a typical pontine lesion may instead be caused by myasthenia gravis, even in the absence of other clinical and electrophysiologic features of neuromuscular deficit.

Journal of Neuro- Ophthalmology 21( 3): 210- 211, 2001. © 2001 Lippincott Williams & Wilkins, Inc., Philadelphia Original Contribution Ocular Myasthenia Mimicking a One- and- a- Half Syndrome Fabio Bandini, MD, David Faga, MD, and Stefano Simonetti, MD A 52- year- old patient developed an eye movement disorder first resembling a left internuclear ophthalmoplegia and subse­quently a " one- and- a- half syndrome" as the presenting symp­toms of ocular myasthenia gravis. No accompanying myas­thenic features were present except for the fluctuation in the amplitude of dissociated nystagmus. This patient shows that an oculomotor disorder considered a typical pontine lesion may instead be caused by myasthenia gravis, even in the absence of other clinical and electrophysiologic features of neuromuscular deficit. Key Words: Pseudo one- and- a- half syndrome- Pseudo inter­nuclear ophthalmoplegia- Myasthenia gravis. Unilateral lesions of the pontine tegmentum affecting the abducens nucleus or paramedian reticular formation and the ipsilateral medial longitudinal fasciculus cause internuclear ophthalmoplegia ( INO) and ipsilateral hori­zontal gaze palsy, a clinical feature known as " one- and- a half syndrome." The most common causes of INO and one- and- a- half syndrome are stroke in the elderly and multiple sclerosis in the young, but brainstem tumors, subdural hematoma, head trauma, and Arnold- Chiari malformation have been reported to produce them as well ( 1). The term pseudo INO was introduced by Glaser ( 2) to designate an INO- like disorder in a patient with myasthenia gravis ( MG). Since then, a few cases of uni-or bilateral pseudo INO in MG have been reported ( 3- 6). We describe a case of an eye movement disorder mimicking at first INO and then a one- and- a- half syndrome in a 52- year- old man that resulted from ocu­lar myasthenia. Manuscript received April 16, 2001; accepted June 7, 2001. Laboratory of Neuro- ophthalmology, Department of Neurological and Visual Sciences, University of Genoa ( FB, DF); and Division of Neurology, E. O. Ospedali Galliera, Genoa ( SS), Italy Address correspondence and reprint requests to Fabio Bandini, MD, Laboratorio di Neuro- oftalmologia, Dipartimento di Scienze Neurolo-giche e della Visione, Universita di Genova, Via A. De Toni 5, 16132 Genova, Italy. E- mail: fbandini@ neurologia. unige. it CASE REPORT A 52- year- old man with a history of hypertension was admitted to our department because of the occurrence of diplopia and blurring of vision on right horizontal gaze. His medications included fosinopril and hydrochlorothi­azide. His neurologic history was unrevealing. On ad­mission, he had impaired adduction OS and a horizontal right- beating nystagmus OD on rightward gaze ( left INO). Although he did not complain of fatigability or fluctuations of the symptoms, the amplitude of the dis­sociated nystagmus varied with each examination. Ocu-locephalic stimulation could not improve the defective eye movements. Convergence was relatively spared. Skew- deviation and ptosis were absent. Leftward gaze and vertical eye movements were normal. The pupils were equal and normally reactive to light and conver­gence accommodation. The optic disks were normal. Monocular distance acuity was 20/ 20. The remainder of the neurologic examination was negative. Two days later, the patient started complaining of dif­ficulty gazing to the left as well. In addition to the above-described findings, leftward gaze palsy was present. Dis­sociated nystagmus in abduction OD was still present and fluctuating in amplitude. This new oculomotor pat­tern was consistent with a one- and- a- half syndrome. Oculocephalic stimulation was again unable to improve the eye movement disturbance. On suspicion of an ex­panding lesion of the left pontine tegmentum, a brain magnetic resonance imaging with gadolinium was per­formed but did not show any lesion in the cerebellum or brainstem or abnormalities of the eye muscles ( not shown because negative but available). Cerebrospinal fluid examination was also normal. Intravenous administration of edrophonium chloride ( Tensilon), 1.0 mg, completely resolved the gaze palsy. A computed tomography scan of the chest with contrast showed no thymus gland. Antibodies to acetylcholine receptor and to skeletal muscle, antinuclear antibody, serum VDRL, and thyroid functions were negative. Re­petitive stimulation ( 3 Hz) of the ulnar, musculocutane­ous, and facial nerves before and after exercise and 210 OCULAR MYASTHENIA AND ONE- AND- A- HALF SYNDROME 211 single- fiber electromyography ( EMG) of the orbicularis oculi were unrevealing. Single- fiber EMG of the ex­traocular muscles was not performed. Negativity of labo­ratory and imaging examinations allowed us to exclude other possible diagnoses, and, based on the positive re­sponse to Tensilon, a diagnosis of ocular myasthenia was made. The patient was given pyridostigmine, starting with 60 mg daily, increased to 180 mg daily. At those doses, there was complete control of the oculomotor symptoms. When last examined, 1 year after the onset of the disease, the patient had a normal neuro- ophthal-mologic examination. DISCUSSION Our patient manifested a neuromuscular eye move­ment disorder that started with a left pseudo INO and later evolved into a pseudo one- and- a- half syndrome, with no accompanying myasthenic features except for the fluctuation in the amplitude of dissociated nystag­mus. The only other case of a pseudo one- and- a- half syndrome owing to myasthenia is the one reported by Davis and Lavin ( 7). In the latter, however, late ptosis occurred that was helpful in the differential diagnosis. This case suggests that, although uncommon, MG should be considered in the differential diagnosis of ocu­lomotor disorders usually associated with brainstem le­sions, including one- and- a- half syndrome. Importantly, this can be the case even in absence of any other mani­festation of ocular myasthenia gravis, i. e., fatigue, ptosis, impaired convergence, and a decremental electromyo­graphic response to repetitive nerve stimulation. REFERENCES 1. Leigh RJ, Zee DS. The neurology of eye movements, 3rd ed. New York: Oxford University Press, 1999: 502- 10. 2. Glaser JS. Myasthenic pseudo- internuclear ophthalmoplegia. Arch Ophthalmol 1966; 75: 363- 6. 3. Spooner JW, Baloh RW. Eye movement fatigue in myasthenia gravis. Neurology 1979; 29: 29- 33. 4. Pierrot- Deseilligny C, Michelin T. Pseudo- ophtalmoplegie inter-nucleaire myasthenique. Rev Neurol 1983; 139: 527- 8. 5. Jay WM, Nazarian SM, Underwood DW. Pseudo- internuclear oph­thalmoplegia with downshoot in myasthenia gravis. J Clin Neu-roophthalmol 1987; 7: 74- 6. 6. Ito K, Mizutani J, Murofushi T, et al. Bilateral pseudo- internuclear ophthalmoplegia in myasthenia gravis. ORL J Otorhinolaryngol RelatSpec 1997; 59: 122- 6. 7. Davis TL, Lavin PJM. Pseudo one- and- a- half syndrome with ocu­lar myasthenia. Neurology 1989; 39: 1553. J Neuro- Ophthalmol, Vol. 21, No. 3, 2001