Abstract
Autoimmune hypothyroidism (Hashimotoʼ s thyroiditis) is a common disease in primary
care. A 58-year-old woman with a history of gastric cancer was referred to our department with a
12-month history of high serum creatine phosphokinase (CPK) concentrations and dyslipidemia
without subjective symptoms. Her voice had been hoarse for ＞ 10 years；however, she
considered this an effect of smoking. Her vital signs were within normal ranges, and her physical
examination findings were unremarkable, except for the hoarseness. Her blood test results
showed that her anti-thyroid peroxidase antibody levels and macro-CPK type 1 exceeded the
upper limit of the reference range. Other blood tests and whole-body contrast-enhanced
computed tomography scan results showed no abnormal findings. She underwent hormone
replacement therapy (HRT). Six months later, her serum CPK concentration had normalized, and
macro-CPK type 1 was negative. Hashimotoʼs thyroiditis with macro-CPK can become negative
after HRT. When Hashimoto's thyroiditis is diagnosed, prioritizing thyroid function treatment
may be necessary, even in the presence of macro-CPK. Physicians should confirm thyroid
function in patients with high serum CPK concentrations or dyslipidemia with no subjective
symptoms.
