Interictal 99mTc-ECD brain perfusion SPECT - An indispensable aid in children with drug-resistant epilepsy

Introduction: Cerebral perfusion and metabolism are coupled in most physiologic and pathologic conditions, which strongly correlate with the intensity of neuronal activity. Imaging of brain perfusion with ictal, peri-ictal & interictal SPECT plays a key role in the localization of epileptogenic region and guidance for the subsequent management, especially in drug-resistant epilepsy, where, EEG, MRI & clinical findings are either discordant or normal. Brain SPECT (Ictal & Interictal) is more sensitive and has a superior temporal resolution, compared to 18F-FDG PET in localizing the seizure onset zone. It can depict abnormalities in regions without any apparent structural abnormality. We have prospectively evaluated brain perfusion patterns with 99mTc-ECD SPECT in children with drug-resistant epilepsy, referred to Nuclear Medicine department, AIIMS, Rishikesh, India.

Methods: Interictal brain perfusion SPECT was performed according to standard protocol, using 0.2 to 0.3 mCi/kg with a minimum dose of 3 to 5 mCi of 99mTc-ECD. Tracer was injected intravenously at rest, during the seizure-free period (>24 Hrs) in supine position and brain SPECT was acquired 45 mins post-injection. Reconstructed images were analyzed by an experienced Nuclear Medicine Physician. Location, as well as the severity of perfusion defects, were noted and correlated with respect to the duration of disease, EEG, clinical and other imaging findings.

Results: A total of 41 patients (32 males & 9 females) with drug-resistant epilepsy with age between 1-18 years were analysed. 21/41 (51%) patients had normal MRI brain study and 11/41(26%) patients had normal EEG records, while in 7 patients both MRI and EEG were unremarkable. Temporal lobe hypoperfusion was seen in all patients. However, 13/41 patients had, other focal areas of hypoperfusion, 13/41 had foci of hyperperfusion in addition to temporal lobe hypoperfusion. In 17/41 patients involvement of one hemisphere was seen and 24/41 showed perfusion abnormalities in both hemispheres. Moderate to severe perfusion defects were seen in 18 patients. In patients with abnormal EEG findings, SPECT findings were truly concordant with EEG in 17/30 (56%) of cases.

Conclusions: In the current study of 41 patients, interictal 99mTc-ECD SPECT revealed perfusion defects in all the cases. It was able to provide additional information for diagnosis in the patient group, when other clinical, lab findings, EEG & MRI were either discordant or unremarkable. Also, in a substantial number of cases bilateral hemispheric involvement and additional findings were noticed. The current study endorses an important role of 99mTc-ECD interictal Brain SPECT, as a noninvasive, feasible technique for localization of epileptogenic focus in children with drug-resistant epilepsy, when other modalities are inconclusive and it can improve the overall outcome of the disease.

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