Creatine Treatment to Relieve Muscle Pain Caused by Thyroxine Replacement Therapy

Abstract

To the Editor: The impact of thyroid deficiency and its reversal by T4 replacement therapy on glucose metabolism remained controversial [1–4]. Small doses of thyroxine (1 µg/kg) normalized most of the intermediary metabolic parameters of thyroidectomized rats [5], while 20-times-higher doses would be needed to depress the high rates of thyroid-stimulating hormone (TSH) release of pituitary via feedback inhibition [6]. Thyroxine levels can be brought up to normal with oral thyroxine pills from 25 to 200 µg/day. Under constant balanced conditions, low levels of thyroid hormones maintain normal intermediary metabolism; insufficient thyroxine administration results in hypothyroidism; and high thyroxine doses cause swinging to hyperthyreoidic symptoms. The regulatory functions of adenohypophysis and pituitary-dependent glands are to smooth out oscillations. In thyroidectomized patients, the negative feedback loop does not function, and the development of hypothyreoidic symptoms are prevented by thyroxine replacement therapy. This letter presents a hypothyroid case where the muscular side effects following thyroxine replacement therapy manifested as muscle pain. Long-term protection against thyroxine replacement therapy-induced muscle pain has been provided by low doses (2 g/day) of creatine monohydrate administration. In 1993, our male patient was 49 years old when his hyperthyreosis was diagnosed. In 2001, the patient had 7–8 kg loss in weight in 6 months and hyperthyreosis recidiva was diagnosed. A single dose of p.o. administered radioisotope 131I (240 MBq) was applied in a capsular form. Three months later (December 2001), laboratory parameters showed high creatine kinase (894 U/L) and transaminase (GOT 65 IU/L, GPT 61 IU/L) activities. Elevated creatine kinase levels may reflect injury in myocardial infarction, muscle breakdown, muscular dystrophy, myositis, reduced adenosine triphosphate (ATP) level in muscle, and acute renal failure. Upon the radioactive destruction of thyroid function, the patient experienced excessive muscle pain and involuntary defecation of stool for several days. …