A Case of Elevation of Serum Creatine Kinase With Antithyroid Medications for Graves’ Disease

We describe a female patient with Graves ’ disease (GD) who had abnormal increases of serum creatine kinase (CK) concentration during treatment with antithyroid medications. She experienced myalgia and manifested increased serum CK levels, with a maximum of 7,925 U / L, 2 - 4 months after initiation of methimazole (MMI) treatment at a dose of 10 - 15 mg / day. After MMI was exchanged for potassium iodide (KI), serum CK levels decreased and the myalgia resolved. However, after KI was exchanged for propylthiouracil (PTU), the myalgia recurred and serum CK levels increased with a maximum of 521 U / L. PTU was discontinued and serum CK levels returned to normal, but hyperthyroidism recurred and the patient did not consent to the alteration of treatment from antithyroid drugs to radioiodine therapy or surgical treatment. PTU was restarted and increased gradually from 50 to 300 mg / day. Serum CK levels did not increase, but the hyperthyroidism persisted. After we exchanged PTU for MMI (20 mg / day) and levothyroxine (25 u g / day), serum CK levels did not increase and the hyperthyroidism diminished. While the mechanisms for this process are not clearly defined, a rapid reduction in thyroid hormones in tissues following chronic hyperthyroidism may result in relative hypothyroid states and subsequent alterations in CK concentration. doi: http://dx.doi.org/10.4021/jem130w