Steroid‐Responsive Morvan Syndrome in a Post‐Thymectomy Generalized Myasthenia Gravis Patient: A Case Report

ABSTRACT Background Morvan syndrome (MoS) occurring after or concomitant with myasthenia gravis (MG) in patients with unresected thymoma has already been reported in the literature. Accordingly, the presence of thymoma may result in decreased immune tolerance, diminished regulatory T cells, and escape of immature autoreactive T lymphocytes, increasing the risk of both conditions. Here we report a young MG male patient in remission who, despite having undergone thymectomy several years ago, still developed the classic signs and symptoms of MoS. Case Presentation Our patient is a male 39‐year‐old AChR antibody‐positive generalized thymomatous MG patient who underwent thymectomy 2 years prior to the current admission. Over the last 6 months, the patient developed severe burning sensation in the hands and feet, insomnia with occasional hallucinations, intermittent high‐grade fever, myokymia, and cramps. Nerve muscle ultrasound showed high frequency to‐and‐fro movement of the muscle fascicles, and electromyogram confirmed it to be myokymia. The involvement of the central, peripheral, and autonomic nervous systems led us to treat the case as MoS, despite not having recurrence of thymoma on the chest CT scan. Conclusion Despite the post‐thymectomy status, there is still a risk of developing MoS among MG patients. Nevertheless, we hypothesize that the symptoms of MoS in these cases can easily be controlled by steroid pulse therapy and medications that suppress hyperexcitability.