¹²³I-IMP SPECT findings in Anti-NMDA receptor encephalitis

Introduction: Anti-N-methyl-d-aspartate (NMDA) receptor encephalitis is a rare autoimmune disorder first described by Josep Dalmau in 2007. Patients have characteristic clinical symptoms that resemble schizophrenia, and are thus frequently initially misdiagnosed with primary psychiatric disorders. Median age at disease onset is 21 years and 81% of patients are female. MR imaging of the brain is unremarkable in 40% of cases. We performed brain single-photon emission computed tomography (SPECT) using 111MBq of N-isopropyl-p-123 I-iodoamphetamine (¹²³I-IMP) as a tracer in patients in the acute and chronic phases of anti-NMDA receptor encephalitis. To the best of our knowledge, no study has yet evaluated the value of ¹²³I-IMP brain perfusion SPECT in anti-NMDA receptor encephalitis. We herein report clinical, MR, and IMP SPECT findings of 4 patients with anti-NMDA receptor encephalitis. Materials and Methods: We performed seven ¹²³I-IMP SPECT scans in 4 patients with anti-NMDA receptor encephalitis from 2015 to 2019 (4 female; mean age 22.0 years, range 19-26 years). All patients had also undergone brain MR imaging. All the brain SPECT and MR images were evaluated by consensus between two radiologists.

Results: ¹²³I-IMP SPECT images showed hypoperfusion in the bilateral occipital lobe in all 4 patients (100%) and hyperperfusion in the left frontal, parietal, and temporal lobe in the acute phase of encephalitis in 1 patient (25%). All of these abnormal findings tended to improve in the follow-up SPECT scan. In contrast, MR images were unremarkable in 3 patients (75%). In 1 patient (25%), hypertrophy of the left cerebral cortex and hyperintensity were observed on T2-weighted MR images.

Conclusions: These cases suggest that ¹²³I-IMP SPECT is more useful than anatomical imaging in the clinical diagnosis of anti-NMDA receptor encephalitis. Radiologists should be familiar with the MR and ¹²³I-IMP SPECT imaging findings, clinical manifestations, etiology, and pathophysiology of anti-NMDA receptor encephalitis, as timely and correct diagnosis can ensure prompt, appropriate treatment and a better clinical course.