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Show Journal of Neuro- Ophthalmology 20( 4): 246- 247, 2000. © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia ' Isolated Inferior Rectus Muscle Palsy Resulting From a Nuclear Third Nerve Lesion as the Initial Manifestation of Multiple Sclerosis Andrew G. Lee, MD, Rosa A. Tang, MD, Gina G. Wong, OD, Jade S. Schiffman, MD, and S. Singh, MD Isolated inferior rectus muscle ( IRM) palsy due to a nuclear or fascicular third nerve lesion is uncommon ( 1- 4), and third cranial nerve palsy as the presenting sign of multiple sclerosis ( MS) is rare ( 5- 9). We report an unusual patient with an isolated IRM palsy caused by a demyelinating lesion in the midbrain seen on magnetic resonance imaging ( MRI). CASE REPORT A 27- year- old woman presented with the acute onset of binocular vertical diplopia on June 20, 1999. She denied any dizziness, vertigo, weakness, or headache. She had no ocular history of trauma or ocular misalignment. Her medical history was significant for anemia, recurrent urinary tract infections, and childhood asthma. Her only medication was an oral contraceptive. Family history was significant for MS in a maternal great aunt. On examination, her visual acuity was 20/ 20 OU. The pupils measured 3.5 mm in light and 6 mm in dark bilaterally. There was no relative afferent pupillary defect. Results of automated ( Humphrey) visual field tests were normal OU. Slit- lamp biomicroscopy, intraocular pressure measurements, and ophthalmoscopy were normal OU. There was no optic atrophy or optic disc edema. Cutaneous sensation to pinprick in the trigeminal distribution was symmetric and corneal sensation was normal bilaterally. Results of neurologic examination were normal. Extraocular motility examination indicated a moderate underaction of the left IRM. There was a left hy-pertropia ( LHT) of 6 prism diopters ( PD) and a 4 PD exotropia ( XT) in the primary position. In right gaze, the deviation measured 2 PD LHT and 2 PD XT and in left gaze, 8 PD LHT and 6 XT. In upgaze there was a 4 LHT and 5 XT and in downgaze there was an 8 LHT and 6 XT. In right head tilt, her deviation measured 7 PD LHT Manuscript received May 19, 2000; accepted July 25, 2000. From the Departments of Ophthalmology, Neurology, and Neurosurgery, The University of Iowa Hospitals and Clinics ( AGL), Iowa City, Iowa; Department of Ophthalmology, The University of Texas Medical Branch ( RAT, JSS, SS), Galveston, Texas; and the University of Houston College of Optometry ( GGW), Houston, Texas. Address correspondence and reprint requests to Andrew G. Lee, MD, Department of Ophthalmology, 200 Hawkins Drive, PFP University of Iowa Hospital and Clinics, Iowa City, IA 52242. and 5 PD exotropia ( XT). In left head tilt, the deviation measured 6 PD LHT and 4 PD LXT. There may have been mild fatigue of the left IRM in downgaze. MRI of the brain showed increased signal intensity on the T2- weighted image measuring approximately 1 to 2 mm within the left dorsal midbrain just ventral to the cerebral aqueduct at the level of the 3rd cranial nerve nucleus ( Fig. 1). This lesion was believed to be consistent with demyelination. Additional periventricular areas of increased signal intensity ( consistent with demyelination) on T2- weighted and fluid attenuated inversion recovery sequences of the MRI were demonstrated. A lumbar puncture showed normal cell count, protein, and glucose, but there were two oligoclonal bands present and an increased immunoglobulin G ( IgG) synthesis rate. Serum antinuclear antibody, erythrocyte sedimentation rate, anti- cardiolipin antibodies, lupus anticoagulant, thyroid function tests, and vitamin B12 level were normal. Visual evoked responses were normal bilaterally. She was treated with a 5- day course of intravenous methyl-prednisolone ( 1,000 mg/ d). Four days after completing her steroids, she experienced resolution of her diplopia. On August 30, 1999, she had a small 3 PD left hyperphoria in primary position but no diplopia, and on February 3, 2000 ( 8 months later), she had only a small residual asymptomatic ( 1 PD) left hyperphoria. DISCUSSION Isolated extraocular muscle involvement caused by a nuclear third cranial nerve palsy is rare ( 1- 5). The differential diagnosis of an isolated IRM palsy includes orbital lesion ( e. g., orbital pseudotumor, tumor, traumatic or postsurgical restrictive disease, thyroid ophthalmopathy); neuromuscular junction lesion ( e. g., myasthenia gravis); and partial third nerve palsy. Although uncommon, brainstem lesions can cause and isolated IRM palsy. Harrison and Wirtschafter ( 10) reported an isolated, unilateral IRM paresis occurring in a patient with a mesencephalic tegmental cavernous angioma. Chou and Demer ( 11) reported a case of isolated IRM palsy secondary to a breast cancer metastasis to the oculomotor nucleus. 246 ISOLATED INFERIOR RECTUS MUSCLE AS INITIAL MANIFESTATION OF MULTIPLE SCLEROSIS 247 FIG. 1. Magnetic resonance imaging ( MRI) of the brain showed an area of increased signal intensity on the T2- weighted image measuring approximately 1- 2 mm within the left dorsal midbrain just ventral to the cerebral aqueduct at the level of the 3rd cranial nerve nucleus ( arrow). This lesion was believed to be consistent with demyelination. The nucleus of the third cranial nerve is composed of various subnuclei. The eyelids ( levators) are innervated bilaterally by a single central caudate nucleus. The Edinger- Westphal nuclei innervate the pupils. The extraocular muscles ( i. e., superior rectus, inferior rectus, inferior oblique, and medial rectus) are served by individual subnuclei. The innervation of the subnuclei is ip-silateral to the respective extraocular muscles except for the superior rectus ( innervated by the contralateral sub-nucleus). The medial rectus subnucleus is quite large, and isolated medial rectus paresis caused by a nuclear lesion is unusual. Thus, nuclear third cranial nerve palsies may present in any of the following ways: 1. Unilateral third nerve palsy with contralateral superior rectus palsy and bilateral ptosis ( single caudate nucleus) 2. Bilateral third nerve palsy with no ptosis ( sparing of single caudate nucleus) 3. Complete bilateral third nerve palsy 4. Bilateral ptosis alone ( but not unilateral ptosis) 5. Isolated weakness of one muscle innervated by the third nerve ( except perhaps the medial rectus muscle) Our patient presented with an isolated left IRM weakness caused by a lesion in the area of the third nerve nucleus. A lesion of the fascicle of the third nerve can not be completely excluded. This lesion was shown on MRI of the dorsal midbrain. The patient had other signs of demyelinating disease, including oligoclonal bands in the cerebrospinal fluid and other periventricular white matter lesions. A presumptive diagnosis of probable MS was made in this patient. Although ocular symptoms occur in up to 83% of patients with MS, isolated cranial nerve palsy as the presenting manifestation of MS is uncommon ( 5- 9). The typical presenting ocular sign of MS is usually optic neuritis. Isolated cranial nerve palsy, however, may be the initial manifestation in up to 5.2% of patients. Th-omke et al. ( 7) reported 14 patients with definite MS with isolated ocular motor cranial nerve palsies ( one third nerve palsy, one fourth nerve palsy, and 12 sixth nerve palsies). Newman and Lessell ( 5) reported an isolated pupil- spared third nerve palsy in MS. Uitti and Rajput ( 6) described a pupil- involved third nerve palsy as the presenting sign of MS. Ksiazek et al. ( 4) described two superior division third nerve palsies and one inferior branch palsy due to intrinsic intra- axial midbrain lesions, one of whom had MS. Rush and Younge ( 9) in a large retrospective series reported that only 2.75% of third nerve palsies were attributable to MS. Patients with MS and diplopia usually have a sixth nerve palsy or an internuclear ophthalmoplegia. These patients also may have saccadic abnormalities and acquired nystagmus. Clinicians should be aware that IRM palsy may be caused by a nuclear midbrain lesion and, although rare, this may be the presenting manifestation of MS. Acknowledgement: This work was supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York, NY. REFERENCES 1. Balcer LJ, Galetta SL, Bagley LJ, et al. Localization of traumatic oculomotor nerve palsy to the midbrain exit site by magnetic resonance imaging. Am J Ophthalmol 1996; 122: 437- 9. 2. Gaymard B, Lafitte C, Gelot A, et al. Plus- minus lid syndrome. J Neurol Neurosurg Psychiatry 1992; 55: 846- 8. 3. Bogousslavsky J, Fox AJ, Carey IS, et al. Correlates of brain- stem oculomotor disorders in multiple sclerosis: magnetic resonance imaging. Arch Neurol 1986; 43: 460- 3. 4. Ksiazek SM, Repka MX, Maguire A, et al. Divisional oculomotor nerve paresis caused by intrinsic brainstem disease. Ann Neurol 1989; 26: 714- 8. 5. Newman NJ, Lessell S. Isolated pupil- sparing third- nerve palsy as the presenting sign of multiple sclerosis. Arch Neurol 1990; 47: 817- 8. 6. Uitti, RJ, Rajput AH. Multiple sclerosis presenting as isolated oculomotor nerve palsy. Can J Neurol Sci 1986; 13: 270- 2. 7. Thomke F, Lensch E, Ringel K, et al. Isolated cranial nerve palsies in multiple sclerosis. J Neurol Neurosurg Psychiatry 1997; 63: 682- 5. 8. Jacobson DM, Moster ML, Eggenberger ER, et al. Isolated trochlear nerve palsy in patients with multiple sclerosis. Neurology 1999; 53: 877- 9. 9. Rush JA, Younge BR. Paralysis of cranial nerves III, IV, and VI: course and prognosis in 1000 cases. Arch Ophthalmol I981; 99: 76- 9. 10. Harrison AR, Wirtschafter JD. Isolated inferior rectus paresis secondary to a mesencephalic cavernous angioma. Am J Ophthalmol 1999; 127: 617- 9. 11. Chou TM, Demer JL. Isolated inferior rectus palsy caused by a metastasis to the oculomotor nucleus. Am J Ophthalmol 1998; 126: 737- 40. J Neuro- Ophthalmol, Vol. 20, No. 4, 2000 |
