Functional neuroimaging could be a valuable adjunct in the differential diagnosis of first-episode manic states, particularly in cases of suspected autoimmune or secondary causes. Of the available techniques, 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) enables the detection of state-dependent variations in cerebral glucose metabolism reflecting affective activation. Starting from the clinical observation of a young patient with a first-episode psychotic mania and frontotemporal hypermetabolism, we conducted a focused literature review conducted according to PRISMA guidelines to contextualize the observed patterns within the framework of bipolar mania and discuss its potential diagnostic and prognostic significance. We report the case of a 20-year-old patient with an abrupt onset of a mania with psychotic features, characterized by disorganized behavior, delusional ideation, emotional lability, and insomnia. A slow response to first-line medications and the occurrence of a first episode of illness, prompted thorough investigations to rule out autoimmune encephalitis and potential correlated pathologies. Magnetic resonance imaging, cerebrospinal fluid analysis, autoantibody panels, electroencephalogram, and whole-body computed tomography were unremarkable. Brain 18F-FDG PET showed marked bilateral frontotemporal cortical hypermetabolism, contrasting with the common metabolic pattern of autoimmune encephalitis. The patient was treated with antipsychotic and mood-stabilizing medications, leading to full symptomatic and functional recovery at three-month follow-up, consistent with a diagnosis of Bipolar I Disorder. This case and literature review suggest that frontotemporal hypermetabolism on 18F-FDG PET may represent a state-dependent functional biomarker linked to the psychotic dimension of mania, beyond a nonspecific correlate of mood elevation. Although PET imaging is not routinely used in psychiatric assessments, its selective application, particularly in cases of suspected secondary causes, may add value by refining the differential diagnosis and enabling earlier initiation of appropriate mood-stabilizing treatments, thereby preventing unnecessary empiric immunotherapy. Prospective, longitudinal, and multimodal studies are warranted to verify its diagnostic accuracy and prognostic value in bipolar mania.
Bottaro et al. (Sun,) studied this question.
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