The Serological Mandate: Bridging the Precision Gap in Neuromyelitis Optica Spectrum Disorders

Introduction

Introduction

When evaluating pharmacoresistant focal epilepsy, we usually rely on three main imaging tools: high-resolution MRI for structural changes, 18F-FDG PET for interictal hypometabolism, and SPECT for ictal hyperperfusion. But using 18F-DOPA PET, which is more commonly used in neurooncology or movement disorders, can yield surprising results. In this case, an unexpected increase in tracer uptake almost led to a mistaken diagnosis of malignancy.

Case Presentation

A 37-year-old man had a history of febrile convulsions and a recent fever, followed by repeated focal seizures with troubling “deja vu” sensations that sometimes spread to generalized seizures. The first EEG showed a spike focus in the left temporal lobe.

However, the structural findings were unclear. MRI showed moderate swelling and a higher T2/FLAIR signal in the left hippocampus, which suggested either limbic encephalitis or a low-grade tumor. While 18F-FDG PET showed the expected interictal hypometabolism at the seizure focus, the ongoing “deja vu” symptoms, even after motor seizures were controlled, led to an 18F-DOPA PET scan to rule out a low-grade tumor.

The scan results were puzzling: there was a mild, widespread increase in 18F-DOPA uptake in the left mesiotemporal region, which matched the MRI abnormalities.

_{Fig 1 : MRI/PET fusion demonstrating co-localized mesial temporal FLAIR abnormality and focal 18F-DOPA uptake in epileptogenic tissue.}

Clinical Analysis: Mechanism vs. Malignancy

This finding creates a real diagnostic challenge. Usually, 18F-DOPA scans in epilepsy show less uptake in both sides of the basal ganglia, which is considered a general response to ongoing seizures. Increased uptake in the cortex is rare and can resemble the pattern seen in gliomas.

One possible reason for this “dopaminergic mirage” is the sudden neurochemical changes caused by the seizure. Human studies often show lower D2/D3 receptor binding in the seizure area, but rodent studies of temporal lobe epilepsy (TLE) have found higher levels of dopamine during seizures. In this patient, the increased 18F-DOPA uptake probably reflects:

• Seizure-induced dopamine transport: a temporary increase in presynaptic dopamine production or amino acid decarboxylase activity in response to repeated limbic seizures.
• Local vasogenic edema: the swelling in the hippocampus seen on MRI suggests a disruption of the local environment, which may allow more tracer to accumulate.

The diagnosis of Mesial Temporal Lobe Epilepsy (MTLE) from hippocampal sclerosis was confirmed over time. Follow-up MRIs showed that the swelling, which looked like a tumor at first, changed into the typical shrinkage of the hippocampus.

_{Fig 2 : Comparative diagnostic framework distinguishing epileptogenic metabolic mechanisms from neoplastic interpretation of focal mesial temporal 18F-DOPA uptake.}

Implications

This case shows that not all focal amino acid uptake in epilepsy means there is a tumor.

• The Utility of ASL: Advanced MRI sequences like Arterial Spin Labeling (ASL) may be crucial; in this case, hyperperfusion (rCBF=2) supported an active seizure focus rather than the typical profile of a low-grade tumor.
• Multimodal findings: If 18F-FDG PET shows low metabolism but 18F-DOPA shows higher uptake, it is important for the clinician to focus on the clinical and EEG context.

_{Fig 3 :  Seizure-driven neurochemical remodeling can produce focal 18F-DOPA uptake that mimics neoplastic metabolic activity in mesial temporal lobe epilepsy.}

Conclusion

The brain’s chemical response to seizures can change over time. This case shows that 18F-DOPA PET results should be interpreted carefully in patients with hard-to-control focal seizures. The unexpected tracer uptake was not due to a new tumor, but was a sign of the seizure’s metabolic effects.

• Increased 18F-DOPA uptake can occur “incidentally” in MTLE and does not always mean there is a tumor.ng surgical decisions based on amino acid PET.
• Follow-up imaging is still the best way to tell the difference between temporary changes from seizures and real tumor growth.

In the end, the dopaminergic system in the limbic cortex changes significantly, and imaging it may tell us more about seizure intensity than about the actual tissue.

Author: Arunit Dey

A surgically inclined medical trainee with a growing interest in brain, spine, and cardiothoracic systems, aspiring to build a career in advanced operative care. He aims to become a patient-centered surgeon who integrates evolving medical technologies with precise clinical judgment. With a strong foundation in surgical sciences, he has gained clinical exposure through case postings involving breast pathologies, chronic ulcers, and diabetic foot, along with observational experience in hernia repair, appendectomy, and cholecystectomy. Academically, he has assisted research work on breast cancer and developed a case report on a complicated hernia surgery, alongside contributing multiple review articles across disciplines. He is currently engaged in ongoing research exploring the role of nutrition in health and disease. MBBS (MS4) GMC Nagpur, India