Limbic encephalitis - small cell lung cancer

Case contributed by Andrew Dixon
Diagnosis almost certain


Seizures and memory loss.

Patient Data

Age: 70 years
Gender: Male

MRI Brain


Subtle abnormal high T2 and DWI signal within the left mesial temporal lobe. No abnormal enhancement.

PET Scan (FDG)

Nuclear medicine

Markedly FDG avid abnormality within the left mesial temporal lobe corresponding to the MRI abnormality. An additional FDG avid focus is seen at the right lung hilum. 

CT shows a right hilar / trachoebronchial soft-tissue mass corresponding to the FDG avid tissue on PET scan. 

Case Discussion

The differential diagnosis for abnormal mesial temporal signal without enhancement on MRI is broad and includes infarction, HSV encephalitis, status epilepticus, low grade astrocytoma, gliomatosis cerebri and limbic encephalitis

The marked FDG avidity on PET scan and right hilar mass however strongly favor the diagnosis of paraneoplastic limbic encephalitis. Small cell lung cancer (as was diagnosed in this case on transbronchial biopsy) is the classic cause of limbic encephalitis however many other tumors can also cause the phenomenon. 

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