Limbic encephalitis and hyperactive foci on PET scan

Two cases of patients with paraneoplastic limbic encephalitis, difficult to control seizures, and unilateral hippocampal hypermetabolism on positron e mission tomography (PET) are described. Two women aged 33 and 61 presented with uncontrolled complex partial seizures, profound memory loss and cognit ive decline. One was later diagnosed with breast cancer and the other with lung cancer. Video-EEG on the first patient recorded multifocal sharp waves and bilateral independent seizure onsets. The second patient had no epilep tiform discharges and bitemporal ictal onset, even though the clinical seiz ures suggested a right temporal onset. Magnetic resonance imaging (MRI) was normal in both patients. PET scans obtained in the interictal state showed right hippocampal hypermetabolism in both patients. In the second patient, the lung cancer was irradiated with resolution of seizures and improvement of memory function. A PET scan six months later was normal. Subsequent sei zure recurrence and worsening of memory led to the discovery of widespread metastases. Limbic encephalitis should be considered in the differential di agnosis of intractable partial epilepsy, particularly if accompanied by sev ere memory loss and cognitive decline. Treatment of the underlying cancer m ay be lead to improved seizure control. Hippocampal hypermetabolism may be a common feature on PET, and may indicate subclinical seizure activity. (C) 1999 BEA Trading Ltd.