methimazole and Muscle-Cramp

Here, we reported two cases with hyperthyroidism who complained of myalgia and muscle cramps during treatment with methimazole tablets (or Thyrozol, the brand name). One case experienced muscle cramps after taking Thyrozol for 6 months, and by this time the patient's thyroid function had returned to normal. In the other case, pain caused by muscular cramps began after the patient took Thyrozol for two weeks and the patient's thyroid function had not returned to normal yet at the time. In both cases, pain caused by muscle cramps appeared while the patients were taking Thyrozol. The myalgia persisted in spite of a reduction in the Thyrozol dose, but was significantly relieved with the discontinuation of Thyrozol. Myalgia and muscle cramps did not recur after the patients were switched to methimazole ointment. There was a strong temporal association between oral administration of Thyrozol and pain caused by muscle cramps, which may indicate that myalgia and muscle cramps are adverse reactions of Thyrozol. Looking into the relevant literature on the topic, we explored in this report the possible mechanisms of the onset of muscle cramps associated with Thyrozol, and compared the adverse reactions of two different formulations of methimazole, intending to provide more clinical experience for the treatment of hyperthyroidism and the management of rare adverse reactions related to antithyroid drugs.

Topics: Humans; Hyperthyroidism; Methimazole; Muscle Cramp; Myalgia; Tablets

Myopathy is a known complication of hypothyroidism, commonly characterized by an elevation in Creatine Kinase (CPK) due to increase capillary permeability proportional to the hypothyroid state. Thyroid hormone is important for the expression of fast myofibrillar proteins in the muscle. In hypothyroidism the expression of these proteins are deficient and there is an increase accumulation of slow myofibrillar proteins. A rapid or abrupt descend in thyroid hormones caused by radioiodine therapy after prolonged hyperthyroidism can lead to local hypothyroid state within the muscle tissue, resulting in CPK elevation and hypothyroid myopathy. Hormone replacement leads to resolution of symptoms and normalization of muscle enzymes serum levels.

Topics: Diagnosis, Differential; Edema; Electromyography; Emergencies; Female; Graves Disease; Hormone Replacement Therapy; Humans; Hyperthyroidism; Hypothyroidism; Iodine Radioisotopes; Magnetic Resonance Imaging; Methimazole; Muscle Cramp; Muscle Weakness; Propranolol; Reflex, Abnormal; Thyroid Hormones; Thyroxine; Young Adult

We report a case of thyrotoxicosis with prolonged post-treatment muscle cramp and hypocalcemia. A 36 year-old woman with hyperthyroidism was treated with Methimazole (MMI). As plasma levels of T4 and T3 were normalized, hypocalcemia was noted and severe cramp of skeletal muscle appeared so that the patient was unable to walk. The cramp was gradually relieved as the levels of thyroid hormones re-increased by discontinuance of MMI, and recurred as the hormone levels were normalized by readministration of MMI. The plasma levels of free calcium ion was positively correlated with those of thyroid hormones, and the muscle cramp was worsened with lowering of the calcium level. Serum examination also revealed vitamin D-deficiency, which was probably due to an unbalanced diet of the patient. A therapeutic trial with 1 alpha-vitamin D3 and calcium lactate in addition to MMI improved both thyrotoxicosis and muscle cramp. These findings suggested that hypocalcemia due to vitamin D-deficiency was involved in the exceptionally prolonged muscle cramp associated with the treatment of hypothyroidism in this patient.

Topics: Adult; Cholecalciferol; Female; Humans; Hypocalcemia; Lactates; Lactic Acid; Methimazole; Muscle Cramp; Thyrotoxicosis; Vitamin D Deficiency