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Show Journal of Clinical Neuro- ophthalmology 10( 2): 115- 117, 1990. © 1990 Raven Press, Ltd., New York Postmyelographic Abducent Nerve Palsy in Association with the Contrast Agent Iopamidol John A. Bell, M. D., F. R. C. S., F. C. Ophth., T. C. Dowd, F. R. C. S., F. C. Ophth., G. G. McIlwaine, F. R. C. S., F. C. Ophth., and G. P. H. Brittain, F. R. C. S., F. C. Ophth. Lateral rectus palsy is an uncommon event following contrast myelography. We report such a case, which fortunately proved to be transient, and speculate on its aetiology in terms of the anatomy of the sixth cranial nerve and the possible toxic effects of the contrast agent Iopamidol ( Isovue; ER Squibb and Sons, Princeton, New Jersey, USA; Niopam, E Merk, U. K.). Key Words: Lateral rectus palsy- Contrast myelography- Isovue--- Niopam- Iopamidol- Abducent nerve. From the Department of Ophthalmology, Newcastle General Hospital, Newcastle Upon Tyne; Department of Ophthalmology, Gartnaval General Hospital ( G. G. Mel.), Glasgow, and Wolverhampton Eye Infirmary ( G. P. H. B.), Wolverhampton, United Kingdom. Address correspondence and reprint requests to Mr. John A. Bell at Department Ophthalmology, Newcastle General Hospital, Newcastle Upon Tyne, NE4 6BE, United Kingdom. 115 The occurrence of an abducent nerve palsy is a serious event suggesting a diagnosis of intracranial disease or an elevation of intracranial pressure. Due to the long intracranial course of the nerve it is a palsy that is of little neurologicallocalising value. However, sixth nerve palsy is a rare but well recognised complication of lumbar puncture, spinal anaesthetic, and myelography. It would seem from the literature that agents introduced intrathecally increase the incidence of this event and in this article we associate lateral rectus muscle palsy with the use of Iopamidol, a later generation contrast medium. We found no similar articles on this complication in the literature at the time of writing. CASE REPORT A thirty- three- year- old female patient was involved in a fall at work in which she suffered an injury to her left buttock and leg. Over the following 2 years she suffered from progressively worsening low back pain which radiated down to her left ankle. She was normotensive, her urine was clear of glucose, and full blood count and erythrocyte sedimentation rate were within normal limits. On examination there was no evidence of nerve root irritation; there was no scoliosis or positive sciatic stretch test. There was no deficit of power or sensation in the lower limb and all reflexes were present and symmetrical. All plain x- rays were normal. As her symptoms persisted and remained unexplained, a myelogram was requested. In April 1989, 10 ml of Niopam was introduced intrathecally via puncture between the second and third lumbar vertebrae. The myelogram proceeded uneventfully and was subsequently found to be normal. She complained of severe headache and 116 f. A. BELL ET AL. nausea within a few hours of the investigation and the next day she developed pain behind both eyes. A few hours later she noticed the gradual onset of diplopia and on examination was found to have an isolated left abducent nerve palsy. This was treated with oral dexamethasone 2 mg four times daily and diazepam 5 mg twice daily for 3 days. Her symptoms abated and 2 weeks later her diplopia and lateral rectus weakness had completely resolved. COMMENT Isolated sixth nerve palsies are uncommon events in young adults; they usually occur in the vasculopathic age group of adults > 50 years old and are often found in those suffering with concurrent arteriosclerosis, diabetes mellitus, or hypertension. In a study of 49 young adults between the ages of 15 and 50, the aetiology of acquired sixth nerve palsies was found to be due to vasculopathy in 29%, tumours in 16%, multiple sclerosis in 12%, presumed inflammation in 8%, trauma 6%, postlumbar puncture in 4%, and orbital amyloidosis in 2%. In 22% no cause could be found ( 1). The aetiology of postmyelographic cranial nerve palsy may be considered along two avenues, first the act of lumbar puncture may in itself initiate the event, and second, the contrast agents used in myelography may have an inherent toxicity. Diagnostic lumbar puncture is associated with the well- documented postpuncture triad consisting of headache and ocular and auditory difficulties ( 2). The mechanism for the postpuncture syndrome is probably due to the slow leakage of cerebrospinal fluid from the puncture site. This results in a progressive caudal shift of the brain as it gradually loses its cerebrospinal fluid cushion, causing traction on the meningeal attachments of the brain. These include the cranial nerves, and while downward traction may cause their paresis, most reports of postpuncture cranial nerve palsies show a marked preponderance toward the sixth nerve ( 3). The preferential damage to the abducent nerve has been explained by Wolff ( 4), who described it as being " the weakling of the cranial contents." He suggested that as the sixth nerve negotiates a right angle bend at the apex of the petrous bone it is susceptible to cranial shifts. It has been well shown that any local pressure is as good a block to nerve conduction as any anaesthetic agent ( 5). If the size of the dural puncture is reduced by the use of smaller gauge needles, headaches and other problems can bl" significantly reduced ( 2). The apparent greater risk of complications, following dural puncture involving the introduction of agents, as in spinal anaesthetic or contrast myelography, may in part be due to the greater manipulation of the needle as part of the procedure. In one series ( 1) a case of lateral rectus palsy followed repeated lumbar puncture for epidural obstetrical anaesthesia. It seems probable that the incidence of complications after lumbar puncture is more marked following the introduction of therapeutic or diagnostic agents into the spinal canal ( 6). They may accelerate the progression of an already existing pathology ( 7) or be the result of a toxic effect of such materials. The older type of oil- based contrast media were poorly absorbed from the subarachnoid space and their chronic irritative effects on the leptomeninges have been well described ( 8). The water- soluble contrast media are absorbed from the subarachnoid space within a few hours, yet they can still cause an adhesive arachnoiditis, as demonstrated radiologically by incomplete filling of nerve roots, loss of nerve root definition, and sometimes complete obliteration of the lumbar subarachnoid space ( 9). One would expect that if this were to be the cause of cranial nerve palsy that not one, but several nerves should be involved; isolated sixth nerve palsy may thus require an alternative explanation. Iopamidol is a nonionic monomeric low osmolal contrast medium used for a variety of radiological procedures. Since it became generally available in 1980 it has been shown to be responsible for fewer side effects and equal diagnostic quality in comparison to Metrizamide. It is the cause of a number of mild to moderate side effects such as sleep disturbances and headache, but most pass unnoticed if the patient has been discharged from the hospital. More serious postmyelographic side effects include confusion lasting several days ( 10), aseptic meningitis ( 11), and optic neuritis ( Bateman, DN, personal communication). Iopamidol has been shown to demonstrate a specific toxicity in relation to nervous tissue. In a series of patients examined 1 day after diagnostic lumbar puncture there were no electroencephalographic changes ( 12). However in a group of 35 patients examined 4- 26 h after contrast myelography with Iopamidol, three showed evidence of neuronal excitability and five others either developed slow wave activity or showed enhancement of wave activity already present before myelography ( 13). These effects may explain the odd affinity for the sixth nerve to palsy. The abducent nucleus and nerve occupy a very superficial position in re- POSTMYELOGRAPHIC ABDUCENT NERVE PALSY 117 lation to the fourth ventricle. This communicates directly with the subarachnoid space through the foramina of Magendie and Luschka. It has been shown with the use of dyes that agents introduced by lumbar puncture frequently enter the medulla ( 14). It is thus possible that Iopamidol may exert a direct neurotoxic effect on the abducent nucleus and nerve. The sequence of clinical events in this report with rapid onset of the symptoms and relatively rapid resolution are consistent with this hypothesis. REFERENCES 1. Moster ML, Savino PJ. Sergott RC Bosley TM, Schatz NJ. Isolated sixth- nerve palsies in younger adults. Arch OphthalmoI1984; 102: 1328- 30. 2. Vandam LD, Dripps RD. Long term follow up of patients who received 10,098 spinal anesthetics. Syndrome of decreased intracranial pressure ( headache and ocular and auditory difficulties). lAMA 1956; 161: 586- 91. 3. Thorsen G. Neurological complications after spinal anaesthesia. Acta Chir Scand 1947; 121{ suppl): 1- 272. 4. Wolff E. A bend in the sixth cranial nerve, and its probable significance. Br I Ophtha/ mol 1928; 12: 22- 4. 5. Gasser HS, Erlanger J. Role of fiber size in the establishment of nerve block by pressure or cocaine. Am I Physiol 1929; 88: 581- 5. 6. Miller EA, Savino PJ, Schatz NJ. Bilateral sixth nerve palsy. A rare complication of water soluble contrast myelography. Arch Ophthalmol 1982; 100: 603- 4. 7. Fincham RW, Joynt RJ, Skultety FM. Neurological deficits following myelography. Arch Neurol 1967; 16: 410- 14. 8. Di Cruro G, Fisher RL. Contrast radiography of the spinal cord. Arch NeuroI1964; 11: 12>- 43. 9. Skalpe 10. Adhesive arachnoiditis following lumbar radiculography with water- soluble contrast agents. Neuroradiology 1976; 121: 647- 51. 10. Wallers K, Chaudhuri AKR, et al. Severe meningeal irritation after intrathecal injection iopamidol. Br Med I 1985; 291: 1688. 11. Robinson C Fon G. Adverse reaction to iopamidol. Med I Aust 1986; 144: 553. 12. Harrington MG, McGeorge AP, Ballantyne JP. The effect of lumbar puncture on the electroencephalogram. J Neurol Neurosurg Psychiatry 1983; 46: 283- 4. 13. Lamb JT. Iohexol versus Iopamidol for myelography. Invest RadioI1985; 20( suppl): 537- 43. 14. Fawcett KR. Extra- ocular muscle paralysis following spinal anasthesia. Minnesota Med 1931; 14: 648- 9. 1Clin Neuro- ophthalmol, Vol. 10, No. 2, 1990 |
