Objective: 1)When to suspect an underlying autoimmune process in patients presenting with parkinsonism. 2)To highlight the importance of FDG PET as a complementary exam in addition to LP and EEG when suspecting AE.

Background: Autoimmune encephalitis (AE) and paraneoplastic neurological disorders (PND) presenting as parkinsonism are described just in a few case reports. Early recognition may have a positive impact on the disease course. FDG PET proved to be more sensitive than MRI in detecting CNS inflammation. According to consensus criteria, it is only considered in the diagnostic criteria for definite autoimmune limbic encephalitis, leaving many possible and probable cases undiagnosed. We proposed considering FDG PET as one of the complementary exams in addition to MRI, LP and EEG, in order to make the diagnosis of AE more sensitive

Method: Clinical suspicion of an underlying autoimmune process was based on the sudden unexpected clinical deterioration during the course of a well diagnosed neurodegenerative disorder or on a rapid clinical progression associated with unusual signs like seizures. All patients underwent brain MRI, FDG PET, LP, EEG and whole body scan and or PET scan. We searched for anti-neuronal antibodies in CSF and serum. Patients were treated with IVIG +/- steroids. Clinical improvement was based on UPDRS and cognitive improvement.

Results: Among the eight patients included, four had parkinson’s disease and four were difficult to classify among the established parkinsonian syndromes. Only three had abnormal MRI suggesting encephalitis, whereas seven out of eight had abnormal FDG PET ranging from diffuse hypometabolism to focal hypo or hypermetabolism. LP results showed pleocytosis (48cells/ml) in one patient, and elevated protein concentration in two ( 0,8g/l and 1.33g/l respectively). EEG showed bilateral temporal sharp waves in one patient. A neuroendocrine colon tumor was detected in one patient. Anti-GAD antibodies (Ab) were detected in one patient (15 IU/ml) and anti-VGKC Ab in another (88 pmol/l). All but one metour proposed criteria for seronegative AE. Four out of five patients were diagnose to have possible AE and one with definitive diagnosis. Clinical improvement was seen in six patients.

Conclusion: Clinical presentation remains the most important clue for suspecting AE. In our small series FDG PET seems to be more sensitive than MRI and should be considered as a complementary exam in addition to LP and EEG.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/fdg-pet-a-good-predictive-tool-for-cns-inflammation/