The interictal psychoses of epilepsy: A systematic review of case reports

Abstract Interictal psychosis has long been described as a neuropsychiatric condition secondary to epilepsy. However, there is no chronological relationship with seizures. It differs from schizophrenia since negative symptoms are less prominent, and deterioration of the patient's personality is uncommon. Forced normalization, an antagonistic relation between seizures and psychosis, may be observed, and it is sometimes called alternating or alternative psychosis when there is no electroencephalogram available. The treatment relies on a balance between antipsychotics and antiseizure medications. Surgery is still controversial. This review aims to analyze the existing literature regarding case reports of interictal psychosis. The search performed in the PubMed database for the terms ((psycho*Title/Abstract) OR (schizo*Title/Abstract)) AND ((interictal Title/Abstract) OR (inter‐ictal Title/Abstract)) presented 703 articles, 112 of which met the eligibility criteria. Forty‐six other studies from other sources were included. Eligible articles were sorted according to their format into case reports and non‐case reports. Sixty‐nine patients, on average 34.7 ± 12.9 years old, were studied. More than half (50.7%) displayed neuropsychiatric comorbidities, with psychoses (23.2%) and head trauma (15.9%) being the most reported. Fourteen (20.3%) patients were mistakenly diagnosed with primary psychosis. Twenty (29.0%) had a left hemisphere focus, the majority in the temporal lobe. The largest single subgroup of patients whose neuroimaging exams were available (17.4%) had no abnormalities. A significant percentage (62.3%) presented abnormal electroencephalograms, 12 of those with episodes of forced normalization (17.4%). The delay between epilepsy and interictal psychosis was 13.8 ± 10.2 years (Median 13.5 years). Many patients have their symptoms treated as primary, and forced normalization also complicates the treatment. It is urgent to implement guidelines for diagnosis, theragnosis, and prognosis of this fascinating entity.