Worsening of myasthenia gravis after administration of injectable long-acting risperidone for treatment of schizophrenia; first case report and a call for caution

Myasthenia gravis is an autoimmune disease characterized by muscle weakness due to autoantibodies affecting the neuromuscular junction. Co-occurrence of myasthenia gravis and schizophrenia is very rare and raises a challenge in management of both diseases. Antipsychotic drugs exhibit anticholinergic side effects and have the potentials of worsening myasthenia. Long-acting risperidone is an injectable atypical antipsychotic drug that has not been previously reported to worsen myasthenia gravis in literature. We report the first case report of worsening of myasthenia after receiving long-acting risperidone injection for schizophrenia in a 29-year-old female with both diseases. She started to have worsening 2 weeks following the first injection and her symptoms persisted despite receiving plasma exchange. This could be explained by the pharmacokinetics of the drug. We recommend that long-acting risperidone should be used with caution in patients with myasthenia gravis, and clinicians must be aware of the potential risks of this therapy.