A Case of Myotonia Congenita and Schizophrenia: Difficulties in Treatment with Antipsychotics due to Hypersensitivity to Extrapyramidal Symptoms

Myotonia congenita is a rare non-dystrophic skeletal muscle disease characterized by an inability to relax skeletal muscles after abrupt voluntary movements. Patients with this condition have stiff muscles and difficulty with mobility, especially when initiating movement after periods of rest. It is well known that movement disorders are a common side effect of antipsychotics due to their ability to antagonize dopamine 2 receptors in the extrapyramidal part of the basal ganglia. The purpose of this case is to describe the effects antipsychotics had on a 59-year-old Caucasian male with comorbid myotonia congenita and schizophrenia in an inpatient psychiatric hospital setting. Medication trials of ziprasidone, haloperidol and clozapine exacerbated his myotonic symptoms leading to falls and complaints of severe muscle stiffness, which were relieved upon discontinuation of all antipsychotic medications. This suggests that patients with myotonia congenita may have an increased sensitivity to the extrapyramidal side effect profile of antipsychotics. Treatment options for this patient case are discussed with an emphasis on lamotrigine.