Mr. Lam had been diagnosed with Graves' disease, an autoimmune disorder causing hyperthyroidism, complicated by heart failure and cirrhosis, at another hospital. He was prescribed antithyroid medication to control his thyroid hormones and advised to return for a follow-up appointment after one week to assess the drug's response and monitor for side effects. However, because he experienced no immediate unusual symptoms, Mr. Lam did not return for his follow-up and continued taking the antithyroid medication on his old prescription.

When he began to feel fatigued, experienced muscle pain and weakness, and noticed his urine was dark like tea, he sought medical attention at Tam Anh General Hospital in Ho Chi Minh City. Tests revealed his CK enzymes, indicators of muscle damage, were more than 10 times the normal limit (6,500 U/L). His blood creatinine and urea levels were elevated, accompanied by muscle protein in his urine. Doctor Tran Dong Hai, from the Department of General Internal Medicine, stated that these were characteristic signs of progressive rhabdomyolysis leading to weakness, paralysis, and acute kidney failure. A kidney ultrasound also showed mild cortical medullary hyperechogenicity, a rare complication of antithyroid medication use, which occurred due to improper drug administration.

Antithyroid medications can cause muscle damage through various mechanisms, including direct toxicity to muscle cells (especially mitochondria), abnormal immune reactions, or changes in thyroid hormones that disrupt muscle energy metabolism. Doctor Hai explained, "It is highly probable that Mr. Lam developed rhabdomyolysis because the antithyroid medication interfered with the muscle's energy production mechanism, leading to widespread destruction of muscle cells and the release of significant muscle protein and CK enzymes into the bloodstream." He added that when these substances are too high, the kidneys must continuously filter them, which can easily lead to tubular obstruction and acute kidney failure.

Following a rapid consultation, doctors instructed Mr. Lam to immediately stop the antithyroid medication. They initiated high-speed intravenous fluid administration to dilute the concentration of toxic muscle substances in his blood and increase their elimination through the kidneys. Urine alkalinization was also performed to prevent muscle protein precipitation in the renal tubules, while CK enzymes, creatinine, and blood electrolytes were continuously monitored. The primary goals were to protect the kidneys, enhance the excretion of muscle toxins, and prevent the progression of kidney failure. In the initial 24 hours, he received over 4 liters of fluid, his urine output gradually increased, and kidney function began to improve.

After 5 days of treatment, the patient's muscle damage decreased, and kidney function gradually recovered. Following discharge, Mr. Lam was advised to consider alternative treatments, such as radioactive iodine therapy or thyroidectomy, instead of antithyroid medication.

Doctor Hai examines Mr. Lam during a follow-up visit. Photo: Tam Anh General Hospital

According to Doctor Dong Hai, antithyroid medication is often the first choice for treating hyperthyroidism. However, the drug can have side effects such as agranulocytosis, liver toxicity, and skin allergies. The American Thyroid Association (ATA, 2016) guidelines state that individuals who have experienced rhabdomyolysis due to a specific antithyroid drug should absolutely not use that drug again, as the risk of recurrence is nearly 100%. If a patient cannot tolerate the medication or experiences a relapse, doctors will switch to definitive treatments like radioactive iodine or thyroidectomy.

During the first week of antithyroid medication, patients require close monitoring because this is when muscle and kidney disorders are most likely to appear. Patients should pay attention to unusual signs such as increasing muscle pain, general weakness, reduced urination, or dark urine, and should seek medical attention within 24 hours for muscle enzyme and kidney function checks. For new users of the medication, the typical follow-up schedule is after one to two weeks to assess treatment response and conduct regular blood tests, including CK, complete blood count, and liver and kidney function, allowing for timely dose adjustments or medication changes as needed.

Trong Nghia

*Patient's name has been changed