Precipitation of Carbamazepine-Controlled Seizures Due to Low-Dose Risperidone in a Child: A Conspiracy to Unbalance Blood Electrolytes.

To the Editors: S eizures are a rare adverse drug reaction (ADR) associatedwith the use of several neurological and psychiatric drugs including antipsychotics and, paradoxically, antiepileptic drugs. The mechanism is possibly attributable, among many other causes, to a disruption of the electrolyte balance. Common causes of electrolyte imbalance include the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) and polydipsia, both possibly connected with the use of antipsychotics and carbamazepine or oxcarbazepine. These drugs are implicated in several cases of SIADH and polydipsia throughmechanisms only partially identified. Here, we present and discuss the case of a 7-year-old girl affected by protocadherin-19 (PCDH19) epilepsy due to a mutation in the PCDH19 gene and involving clusters of seizures and behavioral disturbance. Her epilepsy was controlled successfully with carbamazepine until the introduction of low-dose risperidone that rapidly caused a seizure relapse due to electrolyte imbalances. Written consent allowing the use of clinical data for research purposes was obtained from the patient's parents.