Role of (18)F-FDG-PET imaging in the diagnosis of autoimmune encephalitis.

نویسندگان

  • Silvia Morbelli
  • Mehdi Djekidel
  • Swen Hesse
  • Marco Pagani
  • Henryk Barthel
چکیده

Establishing the clinical diagnosis of autoimmune encephalitis can be challenging as patients present with various unspecific symptoms. In a Position Paper in The Lancet Neurology, Francesc Graus and colleagues proposed an initial diagnostic work-up relying on conventional neurological evaluation and standard diagnostic tests such as MRI, CSF sampling, and EEG. This approach would enable clinicians to make a timely diagnosis of “possible autoimmune encephalitis”, allowing initiation of immunotherapy. In a second step, the authors proposed comprehensive antibody testing to help to establish a diagnosis of “probable autoimmune encephalitis” or “defi nite autoimmune encephalitis”, potentially enabling refinement of treatment. With regards to brain imaging, the proposed diagnostic framework solely relies on MRI. However, as acknowledged by Graus and colleagues, limbic encephalitis is known to occur in a relevant fraction of patients with normal or non-specifi c MRI fi ndings. In limbic encephalitis, 18fluorodeoxyglucose (18F-FDG) PET imaging has been reported to typically reveal medial temporal lobe hypermetabolism even in MRI-negative or inconclusive cases, suggesting that it could be more sensitive than MRI (figure). In the Position Paper by Graus and colleauges, this important evidence is mentioned only as a footnote in panel 2. Although we commend the Position Paper, we suggest a stronger consideration of 18F-FDG-PET imaging in supporting the diagnosis of autoimmune encephalitis. This proposal is also supported by results of one of the largest multimodal neuroimaging case series in limbic encephalitis, which demonstrated that 18F-FDG-PET imaging might even have a diagnostic role in patients with autoantibody-negative limbic encephalitis. Furthermore, the differences in PET-based glucose metabolism patterns in such patients support the existence of limbic encephalitis subtypes associated with antibodies that are yet to be identifi ed. Apart from the stated potential of 18F-FDG-PET imaging for improved early diagnosis of limbic encephalitis, we propose the following scenarios in which diagnoses of autoimmune encephalitis could be supported in the future by this molecular imaging approach. First, in limbic encephalitis and in other autoimmune encephalitis subtypes 18F-FDG-PET imaging also shows, in a relevant number of patients, extra-limbic metabolic abnormalities (mainly in the brainstem, cerebellum, or cerebral cortex). These PET findings were associated with clinical symptoms and active disease status more strongly than the MRI fi ndings. Thus, 18F-FDG-PET imaging has the potential to improve estimation of disease severity in patients with autoimmune encephalitis, with implications for follow-up evaluation and therapy monitoring. Second, in the future, 18F-FDG-PET imaging might have a role in the diagnosis of anti-NMDA receptor encephalitis, an entity for which MRI has poor sensitivity. Several 18F-FDGPET imaging studies in these patients have shown metabolic abnormalities in diff erent brain areas, including the frontal, temporal, and occipital lobes, and the basal ganglia, cerebellum, and brainstem. Again, the PET fi ndings were more clearly associated with the clinical picture (ie, basal ganglia involvement and presence of movement disorders), disease severity, and recovery after therapy than the MRI fi ndings. Finally, on a practical note, 18F-FDGPET imaging is an attractive future addition to the proposed work-up for two reasons. First, whole-body 18F-FDGPET imaging is often done in patients with paraneoplastic syndromes to screen for malignancy. Such wholebody imaging can easily be extended to cover the brain without increases in radiation burden. Second, in the past few years, with the introduction of combined PET and MRI systems, many groups have already started to replace MRI with PET–MRI in the diagnostic algorithm for other brain disorders. We encourage feasibility studies for the use of this method in autoimmune encephalitis. We agree that, as a next step, the proposed diagnostic framework for autoimmune encephalitis needs to be tested in clinical practice. Further testing can also provide an opportunity to assess the contribution of 18F-FDGPET imaging in the scenarios discussed here. In parallel, the imaging community needs to refi ne standard procedures for acquisition and reading of PET imaging data in autoimmune encephalitis, and to confi rm the results in large prospective studies.

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عنوان ژورنال:
  • The Lancet. Neurology

دوره 15 10  شماره 

صفحات  -

تاریخ انتشار 2016