Utility of subtraction ictal SPECT when video-EEG fails to distinguish atypical psychogenic and epileptic seizures

This study was designed to evaluate the utility of subtraction ictal SPECT coregistered to MRI (SISCOM) in atypical psychogenic nonepileptic seizures (PNES). Video-EEG monitoring (vEEG) is the gold standard for PNES diagnosis but, like any modality, has limitations. In difficult cases in which the diagnosis is suspected but remains in question after vEEG, a complementary study that could help differentiate epilepsy from PNES would be desirable. Thirteen SISCOM studies performed in patients with a final diagnosis of PNES were retrospectively reviewed. Common indications for SISCOM were semiology consistent with partial epilepsy (9/13), abnormal head MRI (5/13), and reported abnormal routine EEG (5/13). SISCOM was negative in 85% (11/13) of patients and was helpful in increasing the diagnostic certainty of PNES in these exceptional cases.