Ictal and interictal SPECT findings in childhood absence epilepsy.

The purpose of this study was to investigate the informative value of single photon emission tomography (SPECT) in relation to the pathophysiological functioning of the brain during absence seizures and the origin of ictal discharges in idiopathic generalized epilepsies (IGEs). Six patients with childhood absence epilepsy (CAE) were selected for the study and two consecutive SPECT sessions were performed concomitant with EEG recordings revealing normal results and during hyperventilation (HV) studies where the ictal discharges were induced either alone or accompanied by clinical absence seizures. All six patients had ictal discharges in their EEGs during HV and two of them also had clinical absences. SPECT findings during HV revealed an overall increase in the cerebral blood flow (CBF) with significantly higher values as compared to the baseline data. There was no indication for any focal origin in either the interictal or the ictal SPECT findings. Results of the study were supportive for the concept of subcortical origin for the absence seizures and they were also promising for the diagnostic value of ictal SPECT in epileptic cases with undetermined origin as to whether they were localization-related or generalized.

The role of 99Tcm-tetrofosmin in the evaluation of thyroid nodules.

Various radionuclides, including 67Ga, 201Tl and 99Tcm-sestamibi, have been used to differentiate benign from malignant thyroid nodules. 99Tcm-tetrofosmin, a lipophilic cationic radiotracer, and 99Tcm-sestamibi have also been reported to accumulate in thyroid tumours. In this study, we evaluated the role of 99Tcm-tetrofosmin in the differentiation of malignant from benign thyroid nodules. Seventy-nine patients with solitary non-functioning thyroid nodules were included in the study. Fine-needle aspiration biopsy was performed in all patients. Sixty patients were subsequently operated on and 19 patients refused surgery. After the injection of 370 MBq 99Tcm-tetrofosmin, static images at 5, 30, 60, 120 and 180 min were acquired. Both visual and semi-quantitative analysis was performed. On visual interpretation, the nodules with late retention were classified as positive for malignancy and nodules without late retention were classified as negative for malignancy. In the semi-quantitative analysis, regions of interests were drawn over the nodule and contralateral normal thyroid tissue. The average number of counts was recorded and tumour-to-normal thyroid tissue ratios calculated. Post-operative histology revealed 19 malignant and 41 benign nodules. Of the benign nodules, adenomas behaved similarly to the malignant nodules with late retention of tracer, while adenomatous nodules revealed no late retention on delayed images and could be differentiated from malignant tumours. In the semi-quantitative analysis, there was a significant difference in tumour-to-normal tissue ratios for adenomatous nodules and malignant tumours as well as adenomas. We conclude that it is not possible to differentiate between malignant and benign thyroid nodules with 99Tcm-tetrofosmin. However, 99Tcm-tetrofosmin scintigraphy is helpful in selecting nodules that can be cured by surgical intervention.

The effect of P-glycoprotein function inhibition with cyclosporine A on the biodistribution of Tc-99m sestamibi.

PURPOSE: The failure to cure persons with cancer is caused primarily by the development of drug resistance by overexpression of p-glycoprotein. Diverse groups of drugs have been identified, including cyclosporine A, which can reverse drug resistance by inhibiting P-glycoprotein transport. Tc-99m sestamibi is a substrate for P-glycoprotein. P-glycoprotein is normally expressed in biliary canalicular surfaces of hepatocytes and is responsible for the excretion of cationic metabolites from the liver. The aim of the current study was to evaluate the effect of cyclosporine A on the biological distribution of Tc-99m sestamibi in vivo. METHODS: Five patients with alopecia and two renal transplant patients who were treated with cyclosporine A were selected for the study. All patients were examined before and at least 2 weeks after administration of cyclosporine A. Tc-99m sestamibi scintigraphy was performed by obtaining planar abdominal images at 5, 30, 60, 120, and 180 minutes after injection, and the liver-heart ratios were calculated. RESULTS: Plasma cyclosporine A, bilirubin levels, liver enzymes, and creatinine clearance values were obtained from all patients. In three, the plasma cyclosporine A level was increased to more than 400 pg/dl. The liver-heart ratio was increased significantly after cyclosporine A administration (P < 0.01). After cyclosporine A administration Tc-99m sestamibi excretion was delayed and the uptake in the liver was increased. The difference was 17% at 5 minutes and 38% at 180 minutes. Liver retention was greatest in patients with cyclosporine A toxicity. CONCLUSIONS: With a limited number of patients, this study suggests that Tc-99m sestamibi excretion from the liver is mediated by P-glycoprotein, and inhibition of P-glycoprotein transport not only delays liver excretion but also increases the liver uptake of Tc-99m sestamibi. Because this observation deserves further investigation, the inhibition of P-glycoprotein function with nontoxic multidrug-resistance reversing agents may be used as an intervention to increase the tumor uptake of Tc-99m sestamibi and to increase the sensitivity of Tc-99m sestamibi tumor imaging.