The effect of metrizamide on the electroencephalogram: a prospective study in 61 patients

Critical Assessment of Myelography Practices: A Call for Rational Guideline Revision

BACKGROUND AND PURPOSE

Patient preparation for myelography and postprocedural monitoring varies widely between practices, despite published guidelines. Our aim was to examine the current practice variations in discontinuing reportedly seizure threshold-lowering medications before myelography and to assess the reported incidence of postmyelographic seizures.

MATERIALS AND METHODS

An e-mail survey was sent to American Society of Neuroradiology members concerning the number of postmyelographic seizures experienced in the past 5 years, the presence of an institutional policy for discontinuing seizure threshold-lowering medications, and the type of myelographic contrast used. We compared the postmyelographic seizure frequency in the responses.

RESULTS

Of 700 survey responses, 57% reported that they do not discontinue seizure threshold-lowering medications before myelography. Most (97%) indicated never having a patient experience a seizure following myelography. The number of postmyelographic seizures between those who discontinue seizure threshold-lowering medications and those who do not was not statistically significant (OR = 2.13; 95% CI, 0.91-4.98; P = .08). Most (95%) reported using nonionic hypo-osmolar agents.

CONCLUSIONS

Survey results revealed widely variable practices for patient myelography preparation and postprocedural monitoring. We found no difference in reported seizures between those who discontinued seizure threshold-lowering medications and those who did not. In light of our findings, we propose that discontinuing reportedly seizure threshold-lowering medications is not warranted with the current nonionic water-soluble contrast agents and may be potentially harmful in some instances. This work supports revision of existing recommendations to withhold such medications before myelography.

Effect of iomeprol on rat hippocampal slice synaptic transmission: comparison with other X-ray contrast agents

RATIONALE AND OBJECTIVES

All contrast agents should be neurologically safe because although some are not indicated for procedures, such as myelography, just the same they may come in contact with nervous tissue during contrast-enhanced imaging. This is because even when they are intravascularly injected, the presence of undiagnosed blood-brain barrier damage may allow them to penetrate the brain barrier. In the present study, we investigated the neurologic safety of iomeprol by studying in vitro its potential effects on the central nervous system (CNS) synaptic transmission. Other widely used x-ray contrast agents were also assessed for comparative purposes.

METHODS

CNS synaptic transmission was evaluated in terms of evoked field potentials recorded from the pyramidal region of rat hippocampal slices. The field potentials were evoked by electrical stimulation of the Schaffer collateral pathway. The effects of the contrast agents were evaluated in terms of number and amplitude of population spikes (PS) and as the maximal slope of the excitatory postsynaptic potentials (EPSP). The contrast agents were tested at final concentrations of 3, 10, and 30 mg(iodine)/mL in iso-osmolal condition with respect to artificial cerebrospinal fluid (CSF).

RESULTS

Iomeprol, like ioversol, principally exerted a mild inhibitory effect on CNS synaptic transmission, an effect that was preceded by a weak, transient excitation. Iopentol exerted a rapid and complete inhibition of synaptic transmission without showing any excitatory effects. Iobitridol, though belonging to the nonionic monomeric class, exerted, surprisingly, an epileptogenic action at the highest concentration, whereas its inhibitory action was slow and mild. Diatrizoate, as expected, exerted an epileptogenic activity even at the lowest concentration, followed by a marked inhibitory action. Ioxaglate, as expected because it is an ionic though dimeric contrast agent, exerted an epileptogenic action at the intermediate concentration, whereas it barely demonstrated an inhibitory effect at all. All the contrast agent effects observed in the study reversed or tended to reverse during washout.

CONCLUSIONS

Even taking in account the limitation because of the use of an in vitro approach and high contrast agent concentrations, we can conclude that the positive neuro-tolerability of iomeprol is further confirmed by this model as it proved to be devoid of epileptogenic activity and, among the contrast agents exhibiting inhibitory action, it was the contrast agent with the least amount of activity. In addition, contrary to that generally reported in the literature, nonionic, low osmolal contrast agents are not all identical in their neuro-tolerability when assessed in the rat hippocampal slice model.

The effect of iohexol on brainstem auditory evoked potentials. A prospective study on 30 patients

A prospective study was made to evaluate the effect of intrathecal injection of iohexol on brainstem auditory evoked potentials (BAEP) following myeloradiculography, in order to assess its neurotoxicity. Thirty patients who received contrast medium via the lumbar route for myeloradiculography (cervical level = 25 patients, lumbar level = 5 patients) had BAEP examinations before, 2 h and 24 h after myelography. No statistically significant prolongation of absolute and interpeak latencies was found between premyelographic and postmyelographic records. Low incidence (20%) of insignificant clinical adverse effect following myelography was also noted in the same group of patient.

Clinical features, pathogenesis and management of drug-induced seizures

Many classes of pharmacological agents have been implicated in cases of drug-induced seizures. The list includes antidepressant drugs, lithium salts, neuroleptics, antihistamines (H1-receptor antagonists), anticonvulsants, central nervous system stimulants, general and local anaesthetics, antiarrhythmic drugs, narcotic and non-narcotic analgesics, non-steroidal anti-inflammatory drugs, antimicrobial agents, antifungal agents, antimalarial drugs, antineoplastic drugs, immunosuppressive drugs, radiological contrast agents and vaccines. For each of these classes of drugs, this article offers a revision of the literature and emphasises in particular the frequency of the adverse reaction, its clinical presentation, its presumed epileptogenic mechanism and the therapeutic strategy for the management of drug-induced seizures. An attempt is also made to distinguish seizures induced by standard dosages from those provoked by accidental or self-induced intoxication. For some classes of drugs such as antidepressants, neuroleptics, central nervous system stimulants (e.g. theophylline, cocaine, amphetamines) and beta-lactam antibiotics, seizures are a well recognised adverse reaction, and a large body of literature has been published discussing exhaustively the major aspects of the issue; sufficient data are available also for the other classes of pharmacological agents mentioned above. In contrast, several other drugs [e.g. allopurinol, digoxin, cimetidine, protirelin (thyrotrophin releasing hormone), bromocriptine, domperidone, insulin, fenformin, penicillamine, probenecid, verapamil, methyldopa] have not been studied thoroughly under this aspect, and the only source of information is the occasional case report. This review does not address the issue of seizures induced by drug withdrawal.

Triphasic waves in endocarditis

A 45 year old woman with probable bacterial endocarditis was admitted to hospital having presented with a deteriorating level of consciousness and a febrile illness. Among the numerous investigations she underwent was an EEG which showed classical triphasic waves at the peak of her illness, and which reverted to normal as did the patient after treatment with antibiotics. The association between triphasic waves and bacterial endocarditis has never been previously reported.

Serial EEG recordings following intrathecal metrizamide administration

EEG recordings were obtained before and after intrathecal metrizamide injection in 50 consecutive patients who underwent metrizamide myelography or cisternography. EEG tracings were recorded daily until the pattern returned to baseline. One patient (2%) developed seizures. The most frequent EEG abnormality was generalized slowing of various degrees. In 15 patients (30%), the EEG record was normal throughout the study. In 4 patients (8%), EEG disturbances were seen up to the fifth day after the procedure. Patients who had undergone cervical myelography and cisternography had a marginally higher frequency of EEG disturbances than patients who underwent lumbar myelography. The causes inducing these time-related disturbances are discussed, as compared to pharmacokinetics of intrathecally administered metrizamide.

Multiple subcortical haemorrhages following lumbar metrizamide myelography

The case is presented of a patient showing multiple subcortical haemorrhages after lumbar metrizamide myelography. This complication after intrathecally administered metrizamide contrast medium appears not to have been reported before. Several different possible explanations are proposed for the phenomena observed in this case.

Influence of certain factors on the manifestations of the adverse effects of metrizamide myelography

Although metrizamide is now being superseded by other contrast media, the mechanisms of its side effects may be of fundamental importance. One hundred and four consecutive patients with suspected cervical cord or root lesion were studied prospectively for factors which might influence the side effects of metrizamide myelography. Elderly patients were more prone to develop mental confusion. An earlier onset of dizziness and/or vertigo was associated with the lumbar route of intrathecal injection. Perhaps surprisingly, phenobarbitone prophylaxis shortened the duration of confusion and delayed the onset of headaches. Other factors, viz. sex, excess intracranial flow of metrizamide and myelographic blockage were not shown to have a significant influence on the adverse reactions.

Aphasia, apraxia and neurogenic stuttering as complications of metrizamide myelography (speech deficits following myelography)

Aphasia following metrizamide myelography has been reported infrequently. During a seven-month period, we examined two patients who developed Broca's aphasia, apraxia of speech, oral-buccal-facial apraxia and neurogenic stuttering after intrathecal metrizamide administration. In each case, focal neurologic deficits were accompanied by clinical, electroencephalographic and radiologic signs of generalized neurologic disease. Serial speech and language evaluations initially revealed severe deficits that were largely resolved by the third day post-myelography. Out-patient follow-up examinations demonstrated persistence of mild speech and language abnormalities in each case. Our findings suggest that metrizamide may cause longlasting neurologic dysfunction.

EEG changes 24 hours after myelography with metrizamide

A prospective study of EEG changes following metrizamide myelography was made on 34 patients aged 17-79 years. EEGs were recorded just before and 22-26 hours after myelography. Usually 8-10 ml of metrizamide was injected by either lumbar or lateral cervical puncture. The concentration of metrizamide was relatively high. EEGs were abnormal in 15 out of the 20 patients whose baseline EEGs were normal. EEGs deteriorated in 10 of the 14 patients whose control tracings were abnormal. High voltage delta activity and/or a great deal of theta activity were common abnormalities. Three patients showed triphasic waves. No relationships were found between the EEG changes and clinical variables. But central nervous system involvements by metrizamide tended to be accompanied by a severe EEG slowing.

Competitive inhibition of human brain hexokinase by metrizamide and related compounds

We have compared the competitive inhibitory effects of 2-deoxyglucose, glucosamine, N-acetylglucosamine, N-benzoylglucosamine, and the commonly used radiographic and density gradient agent metrizamide (2-[3-acetamido-2,4,6-triiodo-5-(N-methylacetamido) benzamido]-2-deoxyglucose) on the mitochondrial and soluble forms of human brain hexokinase. Metrizamide produces a classical competitive inhibition with glucose for human brain hexokinase, with Kis of 2.8 and 2.5 mM, respectively, for the mitochondrial and soluble forms. Glucosamine exhibited Kis of 0.58 and 0.29 mM, while 2-deoxyglucose exhibited Kis of 0.074 and 0.15 mM and N-acetylglucosamine 0.098 and 0.092 mM for these two forms, respectively. N-Benzoylglucosamine was by far the most effective inhibitor tested, with Ki values of 0.0086 and 0.022 mM, respectively. In order of increasing potency as a competitive inhibitor for mitochondrial hexokinase are metrizamide, glucosamine, N-acetylglucosamine, 2-deoxyglucose, and N-benzoylglucosamine. For the soluble form of the enzyme in increasing potency are metrizamide, glucosamine, 2-deoxyglucose, N-acetylglucosamine, and N-benzoylglucosamine. Since N-benzoylglucosamine was over 100 times more potent than metrizamide, some of the effects of metrizamide could be due to contamination by N-benzoylglucosamine. However, gas chromatography-mass spectrometry analysis of metrizamide did not indicate the presence of N-benzoyl-glucosamine. In addition, column chromatographic separation of commercially available metrizamide and reconstitution of freeze-dried eluate fractions localized the inhibitory effect to the metrizamide peak.

Formed visual hallucinations after metrizamide myelography

About 12 hours after 77-year-old woman underwent metrizamide myelography of the posterior fossa to elucidate the cause of downbeat nystagmus, she developed formed visual hallucinations consisting primarily of brightly colored geometric shapes, cloud formations, and human figures. Her white blood cell count was 26,000/mm3 and her serum creatine phosphokinase level was markedly increased to 438 units/liter. Two days later, the hallucinations had subsided, the white blood cell count had decreased to 17,000/mm3, and the serum creatine phosphokinase level had decreased to 105 units/liter. The hallucinations were probably caused by penetration of the metrizamide into the temporal lobe and visual association cortex.

Neurotoxicity of radiological contrast agents

The most important complications of intravascular administration of contrast agents include idiosyncratic (anaphylactoid) reactions, shock, congestive heart failure, cardiac arrhythmias, acute renal failure, and neurotoxic effects. The incidence of serious neurotoxic effects is low. Entry of contrast agents into the central nervous system normally is limited but may be increased by osmotic opening of the blood-brain barrier with cerebral arteriography or arch aortography. Most neurotoxic effects are thought to represent direct effects of the contrast agent on brain or spinal cord. Adverse effects with arteriography include seizures, transient cortical blindness, brain edema, and spinal cord injury. Most cases of focal brain deficit (other than cortical blindness) are attributed to embolism secondary to the catheter. Seizures may occur with intravenous administration, especially in patients with brain tumors or other processes disrupting the blood-brain barrier. The most important adverse effects observed with myelographic agents include acute and chronic meningeal reactions with iophendylate, and seizures and transient encephalopathy with metrizamide.

A double-blind clinical trial of iopamidol versus metrizamide for lumbosacral myelography

A double-blind study was performed to compare metrizamide with the new iodinated water-soluble nonionic contrast medium, iopamidol, for conventional and computerized tomography lumbosacral myelography. Both contrast agents were used in 30 patients, and were equivalent in terms of image quality and clinical accuracy. Headaches and nausea were less severe using iopamidol. The most striking difference was found in adverse neurobehavioral reactions and associated electroencephalographic abnormalities, which were noted in 17% of the metrizamide group but were not seen with the use of iopamidol. Iopamidol appears to be superior to metrizamide for intrathecal applications. An explanation of the differential neurotoxicity is provided.

Iopamidol vs metrizamide: a double blind study for cervical myelography

A double-blind study was performed on 20 patients comparing the safety and efficacy of Iopamidol and Metrizamide in cervical myelography. The radiographic qualities of the Iopamidol and Metrizamide examinations were equivalent when using the same volume (12 to 13 ml), concentration (200 mg I/ml), and a C1-2 route of administration. The performance of a CT scan on selected patients in specified areas of interest provided additional diagnostic information in some patients (e.g syringomyelia, degenerative spondylosis). The adverse reactions were mild in the Iopamidol group with 4 of the 10 patients experiencing no adverse reactions. The more severe reactions, including disorientation, agitation, dysarthria, asterixis, hyperreflexia and EEG abnormalities were limited to the Metrizamide group with one or more occurring in 2 of the 10 patients studied. Only one Metrizamide patient experienced no adverse reactions. In this study containing a limited number of patients, Iopamidol was shown to be a diagnostically effective and safer contrast medium for performing cervical myelography.

Effect of levomepromazine on EEG and on clinical side effects after lumbar myelography with metrizamide

In patients with lumbago-sciatica levomepromazine is a potent supplement to analgetics in pain treatment. The hypothesis that neuroleptics increase the risk of epileptic seizures after metrizamide myelography was not confirmed in a series of 77 patients, 26 with and 51 without levomepromazine medication, before and after lumbar metrizamide myelography. No differences existed between the groups with regard to the appearance of EEG abnormalities such as slow waves or spikes. Mild side effects were more frequent in the levomepromazine group, except nausea and vomiting. Lumbar metrizamide epidurography in 30 patients did not cause any abnormal EEG.

Competitive inhibition of rat brain hexokinase by 2-deoxyglucose, glucosamine, and metrizamide

The effects of metrizamide on the kinetics of rat brain hexokinase were compared in vitro with those of 2-deoxyglucose and glucosamine. Although metrizamide, 2-deoxyglucose, and glucosamine are known to be competitive inhibitors of approximately equal potency for glucose of yeast hexokinase (Ki approximately 0.7 mM for all three), metrizamide is a much weaker competitive inhibitor (Ki about 20 mM) of rat brain hexokinase than either 2-deoxyglucose or glucosamine (Ki about 0.3 mM for both). This indicates a greater active site specificity of rat brain hexokinase than of yeast hexokinase. Rat brain hexokinase activity is enhanced approximately threefold in the presence of 0.05, 0.2, and 0.8 mg/ml bovine serum albumin, while yeast hexokinase is only enhanced by 50% under these conditions. Despite the high Ki value for metrizamide, interference with glucose metabolism may occur whenever metrizamide is present in much higher concentrations than glucose. Myelography in humans is one such situation.

Transient encephalopathy and asterixis following metrizamide myelography. Case report

A case is presented in which cervicolumbar myelography with metrizamide was followed by transient encephalopathy and asterixis. Metabolic etiology was excluded. A large degree of intracranial penetration of metrizamide was demonstrated by computerized tomography. Residual symptoms persisted for 10 days.

Confusion, myoclonus and speech arrest: epileptic manifestations after metrizamide myelography

The importance of accurate diagnosis of epileptic manifestations, even if unusual, as complications of diagnostic metrizamide exploration of the CSF space is emphasized on the basis of 2 case histories.

Asterixis and encephalopathy following metrizamide myelography: investigations into possible mechanisms and review of the literature

Marked asterixis occurred in two patients following metrizamide myelography. One also suffered generalized seizures and the other had severe stuttering speech for seven days. The spectrum of toxic manifestations of metrizamide is reviewed with emphasis on the unusual lethargy and other depressive effects seen with this relatively safe agent. The hypothesis that metrizamide exerts a ouabain-like effect on the cortical surface was tested. Metrizamide in concentrations as high as 20 mM had no inhibitory effect on rat cerebral K+-para-nitrophenylphosphatase, a partial reaction of (Na+K+)-adenosine triphosphatase. Because metrizamide is a 2-deoxyglucose analogue, a competitive inhibition of hexokinase at the first step in glycolysis was also postulated. Metrizamide was found to competitively inhibit commercial (microbial) hexokinase. The Michaelis constant for glucose rises from 0.13 to 0.25 to 0.33 to 0.91 mM in the presence of 0, 0.4, 1.0, and 2.0 mM metrizamide, respectively. Since the concentration of metrizamide over the cerebral cortex after routine myelography may be approximately 50 mM compared with a glucose concentration of only 3.6 mM (65 mg/dl), it is postulated that impaired brain glucose metabolism may be responsible for some of the toxic effects of metrizamide.