Journal of Neuro-Ophthalmology, June 1986, Volume 6, Issue 2

Spasm of the near reflex mimicking myasthenia gravis.

Spasm of the near reflex and myasthenia gravis both may present as isolated abduction deficits, either unilaterally or bilaterally. Although they each have been mistaken for other more serious causes of neurologic dysfunction, convergence spasm has not been reported previously as mimicking myasthenia gravis. Two cases of convergence spasm were diagnosed initially as myasthenia gravis with positive Tensilon tests. The cases emphasize the need to consider convergence spasm in the diagnosis of any patient with isolated abduction deficits, as well as to suggest that double-blinded Tensilon tests may be unnecessary and possibly misleading.

IOI/Tlwl"r Clil/iml Nt·I/'V·(I/U,II"'/III"'''XY o(2): 111/>-/1111. 19/1/1. Spasm of the Near Reflex Mimicking Myasthenia Gravis Michael L. Rosenberg, M.D. <0 1986 Raven Press, ew York Spasm of the near reflex and myasthenia gravis both may present as isolated abduction deficits, either unilat­erally or bilaterally. Although they each have been mis­taken for other more serious causes of neurologic dys­function, convergence spasm has not been reported previously as mimicking myasthenia gravis. Two cases of convergence spasm were diagnosed initially as myas­thenia gravis with positive Tensilon tests. The cases em­phasize the need to consider convergence spasm in the diagnosis of any patient with isolated abduction deficits, as well as to suggest that double-blinded Tensilon tests may be unnecessary and possibly misleading. From the Neuro-ophthalmology Service, Department of Neurology, Uniformed Services University of the Health Sciences, Bethesda, Maryland. The opinions or assertions contained herein are the private ones of the author and are not to be construed as official or reflecting the views of the Department of Defense or the Uni­formed Services University of the Health Sciences. Address correspondence and reprint requests to Dr. Rosen­berg at the Neuro-ophthalmology Service, Department of Neu­rology, Uniformed Services University of the Health Sciences, Bethesda, MD 20814-4799, U.S.A. 106 Spasm of the near reflex is an entity that is con­sidered infrequently as a cause of an acquired ab­duction deficit (1). Typically, the patients present with diplopia or blurred vision and are found to have unilateral or bilateral limitation of abduction. If the associated miosis is not noticed, the patient may undergo a completely normal neuroradiologic evaluation before the diagnosis is suspected. Simi­larly, patients with myasthenia gravis also may present with an isolated abduction deficit and be thought to have sixth nerve dysfunction requiring extensive evaluation. Although both disorders have been mistaken for similar entities, conver­gence spasm has not been reported previously as mimicking myasthenia gravis. Two patients are reported who presented with complaints of inter­mittent diplopia and findings of abduction deficit on examination. Because of the variable nature of the complaints, Tensilon tests were performed (double-blinded in one case), resulting in total res­olution of the diplopia and a diagnosis of myas­thenia gravis. Because treatment was unsuc­cessful, the patients were re-evaluated and were found to have only "Tensilon responsive" conver­gence spasm as the cause of the abduction deficit. These cases serve to emphasize the importance of considering spasm of the near reflex in any patient with abduction defects, as well as to suggest that double-blinded Tensilon tests may be not only un­necessary but perhaps misleading. CASE HISTORIES Case 1 A 55-year-old female had complaints of inter­mittent diplopia for over 30 years. Examinations had reported consistently intermittent deficiency of abduction bilaterally. She was thought to have ocular myasthenia gravis, and in 1976 a double­blinded Tensilon test was reported to be "mark- CONVERGENCE SPASM MIMICKING MYASTHENIA 107 edly positive," with no response to saline but a total resolution of the diplopia and the exotropia with Tensilon. She was on Mestinon for over 6 months, but stopped the medicine of her own volition. She did not return for re-evaluation until 1983, when she requested additional evaluation for increasing symptoms. Although one physician noted the presence of convergence spasm, a repeat double­blinded Tensikm test was done. Again, there was no response to the initial injection of a placebo, but a total response to the Tensilon "confirmed" the diagnosis of myasthenia. Another trial of Mestinon gained only minimal improvement, and she was sent for neuro-oph­thalmologic evaluation. Evaluation was normal ex­cept for a variable esotropia. Immediately on at­tempted lateral gaze to either side, ductions were normal, but within a few seconds she manifested a marked esotropia. It was noted that every time the esotropia increased, the pupils became miotic. A Tensilon test was done without a control, and im­mediately after injection of less than 2 mg of Ten­silon, the esotropia cleared and the miosis re­solved. She declared how the medicine had cured her again. The next day a 1-ml syringe was filled with sa­line in another room, but brought in with a vial of Tensilon. Both were placed within her view. The test was repeated at a time of maximum esotropia, and again within 2 s the esotropia was cured. In addition, she began to note how she felt hot, sweaty, and somewhat nauseous from the injec­tion. The possibility of her not having myasthenia gravis was discussed with her. She never returned for follow-up. Case 2 A 28-year-old male presented with a complaint of blurred vision and diplopia that was intermit­tent and seemed to be worse when he was tired. His examination was normal except for severe lim­itation of abduction in both eyes. A Tensilon test resulted in a dramatic improvement. He was sent for neuro-ophthalmologic evaluation with a diag­nosis of ocular myasthenia gravis. Examination was essentially as noted previously, except that whenever he was esotropic his pupils were also miotic. A repeat uncontrolled Tensilon test showed a total resolution of miosis and esotropia in less than 2 s after the initiation of the injection. Reassurance was given and the symptoms re­solved over the next several days. DISCUSSION An acquired limitation of ocular abduction often is presumed to be due to a sixth nerve paralysis before other etiologic possibilities are considered. Spasm of the near reflex and myasthenia gravis are both entities that can cause significant diag­nostic difficulty in such a setting, primarily be­cause the diagnoses are not considered. Spasm of the near reflex is a condition that was reviewed first by Cogan and Freese in 1955 (2). It primarily occurs as a functional disorder with symptoms of blurred vision and diplopia, as well as nonspecific symptoms, such as headache, oc­ular pain, and dizziness (2). Because the near re­flex consists of a triad of physiologic responses (miosis, convergence, and accommodation), these three phenomena always will occur together. Whether the primary symptom is due to either a change in accommodation (blurred vision) or in the alignment of the eyes (diplopia), the patient always will manifest the fuIJ triad of the near re­sponse. For this reason, one must be careful to ob­serve the pupil during episodes of diplopia for the diagnostic sign of miosis associated with the inter­mittent abduction deficit. The primary method of treating this spasm has been atropine drops. Although this has been suc­cessful in a number of reported patients, in these patients and in others seen by the author with di­plopia as the primary complaint, it has been un­helpful. Weak minus lenses also have been used successfully to treat symptomatic accommodative spasms (1,2). In the two cases described above, the intermit­tent nature of the abduction deficit suggested the diagnosis of myasthenia gravis. A more common error is ascribing incorrectly an ocular motility de­fect to another condition, when it is in fact due to myasthenia gravis. In addition to mistaking myas­thenia for a single sixth, fourth, or third nerve paresis, myasthenia may mimic a classic unilateral or bilateral internuclear ophthalmoplegia, as well as central nystagmus (1,3-6). The diagnosis once thought of can be confirmed with a simple office Tensilon test. False positive tests in ocular muscle weakness have been reported in several conditions, in­cluding botulism, ocular myositis, Lambert-Eaton syndrome, orbital apex syndrome, pontine glioma, polymyositis, as well as functional dis­orders (7-9). The pathognomonic clue in distin­guishing a myasthenic weakness from spasm of the near reflex is to observe the pupil for the always associated miosis. A further clue may be I elill NtllrO·Ollhthalmol. Vol. fo Nil , lQQ~ 108 M.L. ROSENBERG the rapidity of the response. As the time course of a true response to Tensilon is not known to the patient, he usually will develop, as in the above patients, an immediate response within seconds of injection of the Tensilon. This is non physiologic, and a true response to the Tensilon would not occur for at least 10-30 s. Because of the possibility of false positives, it has become routine to perform Tensilon tests in a "double-blinded" fashion. An assistant typically will prepare two syringes, one with Tensilon and the other with an equal volume of saline. The first unmarked syringe is given to the examiner and the contents injected intravenously. Although the physician may be blinded initially as to what the injection was, it soon must become obvious, as in an adequate test it invariably will cause tearing and fasciculations around the eyes. For similar reasons, the vasomotor changes make it unlikely that the patient will remain blinded. Finally, al­though a formal poll has not been taken, it seems that the saline invariably is given first. I suspect that it was for this reason that Case 1 was able to give consistently "appropriate" responses to the double-blinded Tensilon test. I suggest that if there is any question regarding a placebo effect of the Tensilon, a truly single-blinded test would be I 0", M·II'<I-ol'/rIhnlrnul. Vol. 6. No.2. 1986 adequate in a manner first described by Schwab and Perlo (9). The testing should be done first with a syringe previously filled with saline, but· set next to a bottle of Tensilon so that the patient can see what he "actually" is getting. If the test is neg­ative and a true Tensilon test is needed, then a "second" dose of true Tensilon can be given there­after. REFERENCES 1. Griffin J. F., Wray 5. H.. Anderson D. P. Misdiagnosis ot spasm of the near reflex. Neurology 26:1018-20. 1976. 2. Cogan D. G.. Freese C. G. Spasm of the near reflex. Arch Ophthalmol 54:752-9, 1955. 3. Osher R. H. Myasthenic "oculomotor" palsy. Ann Oph­tl1almo/ 11:31-6, 1979. 4. Rush J. A., 5hafrin F. Ocular myasthenia presenting as su­perior oblique weakness. I Clin Neuro-ophthalmol 2:125-7, 1982. 5. Glaser J. 5. Myasthenic pseudo-internuclear ophthalmo­plegia. Arch Ophthalmol 75:363-6. 1966. 6. Keane J. R., Hoyt W. F. Myasthenic (vertical) nystagmus. lAMA 212: 1209-10, 1970. 7. Susac J. 0., Garcia-Mullin R., Glasser J. 5. Ophthalmo­plegia in dermatomyositis. Neurology 23:305-10. 1973. 8. Wray 5. H., Pavan-Langston D. Are-evaluation ot the edrophonium chloride (Tensilon) tonography in the diag­nosis of myasthenia gravis. Neurology 21:586-93, 1971. 9. Schwab R. S., Perlo V. P. Syndromes simulating myas­thenia gravis. NY Acad Sci 135:350-66, 1966.