Autoimmune encephalitis is a diverse group of neuropsychiatric disorders, which are difficult to diagnose clinically. The disorder presents acutely or subacutely with alteration of consciousness, cognitive decline, seizures, and abnormal movements. Autoantibodies are directed against intracellular antigens or extracellular domains of cell surface proteins, critical for neuronal excitability. 18F-FDG PET/CT has been used to diagnose the metabolic derangement in the brain due to various antibodies. Here we describe a case where acute and subacute phase of disease was visualized on serial 18F-FDG PET/CT.
Purpose To study the imaging patterns of Posterior cortical atrophy (PCA) and Dementia with Lewy bodies (DLB) on fluoro-deoxyglucose positron emission tomography computed tomography ([18F]FDG PET/CT), identify areas of overlap and differences and to develop a prediction model to assist in diagnosis using univariate and multivariate analysis. Methods A retrospective analysis of 72 patients clinically suspected of having posterior dementia was done. All patients underwent [18FF]FDG PET/CT of the brain and dopamine transporter imaging with [[99mTc]TRODAT-1 SPECT scan on separate days. The patients were divided into PCA with normal TRODAT uptake (n=34) and DLB with abnormal TRODAT uptake (n=38). The FDG PET/CT uptake patterns were recorded and areas of significant hypometabolism by z score analysis were considered as abnormal. Receiver operator characteristics (ROC) curve analysis was used to determine cutoff z scores and binary logistic regression analysis was used to determine the Odds ratio of being in the predicted groups. Results Significantly hypometabolism was found in parieto-temporo-occipital association cortices and cingulate cortices in PCA patients. DLB patients showed significantly reduced uptake in the visual cortex. No significant difference was found between z score of occipital association cortex which showed hypometabolism in both groups. The cut-off z-score values derived from the ROC curve analysis were as follows- parietal association (cut-off-3, sensitivity-65.6%, specificity - 68.7%), temporal association (cut-off-2, sensitivity-78%, specificity-75%) and posterior cingulate (cut-off-0.5, sensitivity-93.7%, specificity-40.6%), their respective Odds ratio (with 95% confidence interval) for being in the PCA group as derived from univariate logistic regression were 3.66 (1.30–10.32), 10.71 (3.36–34.13) and 7.85 (1.57–39.17). The cut-off z score of primary visual cortex as derived from ROC curve was zero with sensitivity of 87.5%, specificity of 71.9%, and the Odds ratio for being the in the DLB group was 24.7 with 95% confidence interval of 5.99–101.85. Conclusion [18F]FDG PET may be useful as a non-invasive diagnostic modality in differentiating the two posterior cortical dementias, despite significant overlap. Primary visual cortical hypometabolism can serve as an independent diagnostic marker for DLB, even in the absence of TRODAT imaging.
We report a case of 34-year-old woman presenting with complaints of abnormal posturing of hand and tonic-clonic seizures of few days’ duration, which soon progressed to psychotic episodes and injuries secondary to fall/abnormal movements. She underwent 18F-FDG PET for a suspicion of encephalitis, which revealed increased FDG uptake in the bilateral parietotemporal lobes (right more than left), anterior cingulate cortex, bilateral basal ganglia, thalami, and cerebellum. This atypical pattern did not conform to any known pattern of encephalitis, which was later attributed to the presence of both anti-NMDAr and anti-GAD antibodies in blood and cerebrospinal fluid.
A 25-year-old woman with intractable seizures underwent FDG PET/MRI for seizure focus localization. MRI demonstrated bilateral carpetlike nodular subependymal gray matter and asymmetrical focal dilatation in the right temporal horn. PET/MRI showed increased FDG within subependymal gray matter with significant hypometabolism in right anterior temporal lobe. EEG and ictal semiology confirmed the right temporal seizure origin. This case highlights the importance of identification of gray matter heterotopia on FDG PET/MRI.
Early diagnosis is imperative for adequate management of patients with osmotic demyelination syndrome (ODS), which is usually a result of rapid shifts of osmolality secondary to rapid correction of hyponatremia. Magnetic resonance imaging (MRI) with its special sequences is the investigation of choice for early detection of the osmotic changes in the brain. We report a case of clinically suspected ODS with noncontributory MRI and positive fluoro-2-deoxy-d-glucose positron emission tomography (FDG PET) scan with statistical parametric mapping (SPM) analysis, which localized the focal hypermetabolism in the basal ganglia, thalamus, pons, and cerebellum.
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