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Show J. Clin. Neuro-ophth<1/mo/. 2: 125-127, 1<)1\2. Ocular Myasthenia Presenting as Superior Oblique Weakness JAMES A. RUSH, M.D. FRED SHAFRIN, M.D. Abstract We diagnosed ocular myasthenia in a 39-year-old man whose presenting symptom was vertical diplopia. Unrecognized weakness of the right superior oblique and secondary overaction of the right inferior oblique caused a right hypertropia, which was worse on left gaze. One week later left blepharoptosis, right medial rectus weakness, and bilateral obicularis oculi weakness were found on ocular examination. All findings were partially reversed by the injection of Tensilon. Superior oblique muscle palsy simulating a fourth cranial nerve palsy is infrequently reported in patients with ocular myasthenia. Pseudofourth nerve palsy is another sign of myasthenia gravis. Introduction Myasthenia gravis may involve a single muscle or any combination of extraocular muscles in one or both eyes, but to our knowledge the .appear.ance of superior oblique dysfunction .as a presenting symptom of ocular my.asthenia has not been previously reported. We examined a patient with vertical diplopia due to an apparent right fourth cranial nerve palsy, whose ocular my.asthenia was diagnosed by a positive Tensilon test. Case Report We examined a 39-year-old previously healthy man who had a 2-week history of p.ainless vertic.al diplopia. Initi.ally intermittent, the diplopi.a bec.ame continuous .and w.as worse on left g.aze. The ocular examin.ation w.as normal except for the presence of a v.ari.able right hypertropi.a of 4-prism diopters in primary position that increased to lC?-prism diopters on left gaze. No other ocular .abnorm.ality WclS found. Skull roentgenogr.ams and brain computed tomograms were norm.a!. Painless left blepharoptosis developed, and the patient was referred to the University of South Florida, Department of Ophthalmology. From the Departments of OphthalmoloKY, Univ""ity ,.f South Florida College of Medicine, T..mp.., Florid," June 1982 Visu.:sl acuity was 20/15 in both eyes. The pupils were normal. Abnormcllities on ophthalmic examination were confined to the extraocular muscles. In prim.ary position there was an 18-prism diopter right hypertropia and 10-prism diopter left exotropi. a. On left g.aze the hypertropia increased to 30prism diopters, and was accompanied by inferior oblique overaction (Fig. 1). The right medial rectus WclS minim.ally paretic and demonstrated mild slowing of saccadic refixation to optokinetic drum testing. The right eye in adduction demonstrated mildly impaired depression. A three-step test using d red maddox rod confirmed a right superior oblique weakness. There was 3-mm left blepharoptosis, which did not increase on sustdined upgaze. No lid-twitch sign ' was demonstrated. Both obicularis oculi muscles were mildly weak on forced lid closure, but no "peek" sign~ was demonstrated. An intravenous injection of 10 mg Tensilon effected improvement in all the motor findings (Fig. 2). A neurologic examination found no evidence of gener.alized myasthenia gravis. Serum values for T3, T4, T7, and dntinuclear antibody were all normal or negative. A chest roentgenogram was normal. Treatment with mestinon was instituted. Comment Typically ocular myastheni,l causes a v.Hi-lble pattern of diplopi,l ,lOd blephMoptosis, which does not fit .a pattern of ,1 peripher-ll nerve lesilm. ' However, SCh,ltz has I'lbeled ocular mY.lstheni.l "the great masquerader," which he has seen to simulate an clcute third nerve palsy.;' To the best of our knowledge a pseudotrochlear nerve palsy has not been described in patients with l)cul-lr mY-lStheni- l. In our p,ltient, we.l"ness l)f the right superior obliljul' muscle W,lS the presenting symptom of ocular my.lstheni,l. Most patients with ,1 superior oblique muscle weakness h.lVe trochleM nerve dysfunction due to an underlying congenit.ll or trau'matic cause:' but traum,ltic or congenit-ll considercltions in our patient were excluded by history. When left blepharoptosis developed, an intracranial lesion was suspected, and the referring ophthdlmologist obtained a crani.al computed tomogram, which was negative. 125 Fi~ure I. 1','111'1\1, b...-hll't· lI'l1r,wcn,'V" Illlt'dU,ln ,., I,Jn'rhl'n1um "hl"nJ" d"l1hll'..lr"'h'" ''''l'r.h.thH\ III Ihl' n~hl Inlt'n"r 'll"tilloiVe.' Jnd rh.""" 'If the Ic,tt urpt'r ,,"vclIJ FiKUrf! 2. Allt'r IIllr.l\',,'lhIU" ml"" IIl'l\ l,f ,'dh'ph,'1nlllm ,hl,-rll,it- the.' 1,.'\,\.'r.1\ Ih,'" "f th(' rt~ht InfE'ri\"r ,.t,ht..llU' ,inti th", 1,'11 bh'ph.'h'ph'''l'' .Ifl,' (l,·h\'('J Bll'rh.m'pto~I" .1 h.lllm.Hk nl "l'ulM lTIy.lstheni.l. mJy .lffe("1 ,'ne "r bnth t·yes' .md l'h.H.llterbtic.llly Incr('.,~('~ on ,u~I.lil1ed upg.IZ('. presull1.lbly In'll1 fJti~u(,.:' Although Irv.lh'r btigu(' IV.IS .Jbs...nt in our p.I!i"nt. till' rr('s('nn' "f .Jdditi"Il.JI (',tr.wl'uIM mu" It, "gn' ,ugg('~t('d thl' n.rn'ct di.lgnosis. (.I.,,(·r h,l' h.und m('d,.11 r('l·tll~ w....lkl1('s. tl' be ,lImll"'" "' hI' ".lllI'llt, IVlth llnd.H my.lsthrlli.I'; .Ind h.JS previously described the phenomenon of p. eudllinternucle.H ophthalmoplegia,; Our patient h.ld.J mild exotropia and right medial rectus weakIl(' ss. which was ,JUgmented by optokinetic testing. A refix.Jtion lag of the medial rectus has been demonstrJted in patients with subtle internuclear l'phthalmoplegia" and was evident in our patient. whose findings simulated a pseudointernuclear Journal of Clinicdl Neuro-ophthalmology ophthalmoplegid without .lbducting nyst,lgmus. The frequent p.lrticip.ltion of the obicul.uis lKuli muscles in the we.lkness of l)Cubr my.lsth<'ni.l'; c.m be identified in the suspel-t p.ltimt. When thl' patient attempts forced lid closure. the I'x.llllinN can demonstr.lte obicul.lris we.lkne S bv successfully separating the upper .md the low~r eyelids. Moderate weakness l)f both obicul.nis llculi muscles was readily demonstrJtl'd in our p.ltient. Unequivocal strengthening of onl' or ml)re w<'.lkened extraoculJr muscles .lfter the intr.wenous injection of 10 mg edrophonium chloride (Tensilon) is p,lthognonwnic l)f my.lstheni.l gr.wi.. In ()ur patient. strengthening of the left lev.ltor p,llpebr,H' superioris. right medi.ll rectus. ,lnd both obicularis oculi occurred in response to the injection of edrophonium. We suggest th,lt this maneuver. if performed earlier in the patient's couse. would have spared the patient needless clOd costly tests. References I. Cogdn. D.G.: MYdsthenid grdvis. A review of the disedSe and .I description of lid-twitch .IS .I chdrac- June 1982 Rush. Shdfrin t«ristie sign. Arch. Ophthdlmo/. 74: 217-221. 1965. 2. Oshl·r. 1~.H.••:md Griggs. R.C.: Obiculdris fdtigue. Arch. Ophth.l/mo/. 97: 077-079. /979. J. Seh.lt7.. N.: PrCSl'nl«d .It the Ameri .In ACddemy of Ophth.llnwlogy. NovrmbN I. 1981. Atlantd. GeorgiJ. 'I. Rush, I.A .. .lnd Young«. B.R.: Pdrdlysis of crdnidl nt'rvl' Ill. IV.•JnJ VI. ('dusr .Ind prognosis in /,000 C.ISl'S. Arch. Uphth.l/mo/. 99: 70-79. 1981. S. Gorrlick. I'.B.. Rosrnbcrg. M.. dnd I'dgdno, R.J.: [nh.lllcrd ptosis in mydstheni.l grdvis. Arch. Neuro/. 38: 5J I. 19~ I. o. GI.lst'r. 1.5.: 0 uldr mydsthenid grdvis. In Symposium tin Neuro-ophth.l/moioxy, Tr<lnsdctions of the N('w Or/e.3Ils AC.ldt'my (If Ophth<l/m%gy. St. Louis, The C.V. Mosby Co., 1970. pp. 232-240. 7. GI.lst'r. J.S.: MYdsthenic pSl'udo-intt'rnueleor ophthdlmoplegid. Arch. Ophth.l/moJ. 75: 303-360. 1900. 8. Smith. I.l.. dnd Ddvid. .J.: InternueleM ophthdlmoplegid. Two new c1inicdl signs. Neurology 14: 307-309. 1904. Write for reprints tv: lames A. Rush. M.D., 12901 North 30th Street. Box 21. UniverSity of South F10ridd College of Medicine. Tdmpd. F10ridd 33012. 127 |
