A 58-year-old woman with a remote history of breast cancer presents with a 4-week history of progressive memory loss, confusion, paranoid delusions, and focal seizures with olfactory auras. Brain MRI shows bilateral medial temporal lobe T2/FLAIR hyperintensities. The EEG pattern marked **C** in the diagram (bitemporal slow waves, epileptiform discharges, and frequent focal temporal seizures) is documented. CSF analysis reveals mild lymphocytic pleocytosis and elevated protein. Serum and CSF antibodies are positive for GluA1/GluA2 subunits. Which of the following best explains the mechanism of neuronal dysfunction in this patient?
A. Antibody-mediated internalization of AMPA receptors leading to decreased glutamatergic synaptic transmission and impaired hippocampal memory processing
B. Direct inhibition of GABA synthesis in interneurons causing disinhibition and seizure generation
C. Antibody blockade of NMDA receptors resulting in excitotoxic calcium influx
D. Complement-dependent lysis of hippocampal pyramidal neurons causing acute neuronal death
Explanation
Why option 1 is correct
The clinical presentation—subacute memory loss, confusion, psychiatric symptoms, and temporal lobe seizures with bitemporal EEG abnormalities (marked C)—is pathognomonic for anti-AMPA receptor encephalitis. The GluA1/GluA2 antibodies cause internalization and removal of AMPA receptors from the postsynaptic membrane, reducing fast excitatory glutamatergic neurotransmission. This is particularly damaging in the hippocampus, the core structure for memory consolidation, explaining the prominent short-term memory loss and limbic syndrome. The bilateral medial temporal lobe MRI changes and bitemporal EEG findings directly reflect this hippocampal pathology. (Graus et al., Lancet Neurol 2016)
Why each distractor is wrong
Option 2: While some autoimmune encephalitides involve complement-mediated neuronal lysis (e.g., NMDA receptor encephalitis with severe cases), anti-AMPA receptor disease primarily operates through receptor internalization and functional loss, not acute neuronal death. The preserved brain structure on MRI and the subacute course argue against acute lytic injury.
Option 3: NMDA receptor antibodies, not AMPA receptor antibodies, are the target in NMDA receptor encephalitis. NMDA blockade does not explain the pattern of memory loss and temporal lobe seizures seen here; moreover, this patient's antibodies are specifically against GluA1/GluA2 (AMPA subunits).
Option 4: While seizures are prominent, the primary pathology is not GABAergic dysfunction but rather loss of excitatory drive due to AMPA receptor internalization. GABA synthesis inhibition would cause a different clinical phenotype and is not the mechanism of anti-AMPA receptor disease.
High-YieldNEET PG
Anti-AMPA receptor encephalitis = antibody-mediated AMPA receptor internalization → loss of fast glutamatergic transmission → limbic syndrome with prominent memory loss and temporal lobe seizures; ~70% paraneoplastic, especially breast cancer and SCLC.
Graus et al., Lancet Neurol 2016, Autoimmune Encephalitis
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