Graves' disease associated with spasmodic truncal flexion

A 40-year-old Chinese man was admitted with 1–2 Hz spasmodic truncal flexion resembling myoclonus. He was known to be thyrotoxic, and had defaulted antithyroid therapy. Clinical examination revealed truncal flexion from contraction of the rectus abdominis, with no involvement of limbs or face and no jerking in sleep. He was biochemically thyrotoxic. Treatment with clonazepam and propylthiouracil resulted in resolution of the myoclonic jerks within the next 3 weeks. He stopped taking clonazepam within the next 3 months with no recurrence of myoclonus. He remained well until he stopped taking his antithyroid medications 9 months later, when he developed spasmodic truncal jerking again. Biochemical tests confirmed that he was hyperthyroid at this time. These movements ceased within a month of compliance with antithyroid therapy, and he has been well since. MRI of the brain and thoracic spine were unremarkable. Thyrotoxicosis is known to cause chorea and tremors, and has rarely been described in association with myoclonus.