Bone and Calcium Metabolism in Subclinical Autoimmune Hyperthyroidism and Hypothyroidism

Abstract

Abstract. Bone turnover is reported to increase in favour of resorption in overt hyperthyroidism and the rate of resorption is associated with the levels of thyroid hormones. Hypothyroidism, on the other hand, was shown to cause no disturbance of calcium kinetics and found to associate lower trabecular resorption surfaces and increased bone cortical thickness. Similar studies are very rare in subclinical thyroid disorders and consequently we aimed to examine calcium and bone metabolism in subclinical thyroid disorders. Thirteen patients with subclinical hyperthyroidism secondary to untreated Graves' disease, 20 patients with subclinical hypothyroidism and 10 healthy subjects participated in this survey. Briefly calcium, phosphorus, and creatinine (Cre), urinary deoxypyridinoline (U-DPD) and serum osteocalcin (OC) were measured as biochemical markers for calcium metabolism. Concerning serum Ca and phosphorus levels, there were no differences between three of the groups, but urinary Ca excretion was higher in subclinical hyperthyroid patients compared to control and hypothyroid subjects. Hypothyroid patients had similar U-DPD levels with control subjects (p = 0.218). Serum OC and U-DPD were higher in subclinical hyperthyroid compared to control subjects ( p<0.001 and p<0.001 respectively). We demonstrated a higher bone turnover and greater calcium excretion in subclinical hyperthyroid patients. Additionally, we found that subclinical hypothyroidism is not associated with disturbed calcium metabolism. As persistent increase in bone turnover is responsible for accelerated bone loss, patients with Graves' disease may have increased risk for osteoporosis. THE combination of an undetectable serum thyrotropin concentration, as measured by an assay with a threshold of detection 0.1 mU per liter or less, and normal serum triiodothyronine and thyroxine concentrations (usually at the upper end of the normal range) is known as subclinical hyperthyroidism. It is not a rare finding; rates between 0.2% and 11.8% have been reported in different groups, according to age, sex, etc [1]. The etiology is usually the same as that of overt hyperthyroidism [1]. The health implications include general symptoms, effects on the cardiovascular system, and decreased bone density. Subclinical hypothyroidism is defined as a state where the patient is eumetabolic but has a modest increase in the serum TSH level (5 to 15 mU/L), a normal serum T 3 concentration, and low-normal or slightly decreased serum fT 4 levels. The overall prevalence has been reported to range from 4-10% in large general population screening surveys [2].There are a few studies performed to examine calcium and bone metabolism in subclinical thyroid disorders with conflicting results. Bone turnover is increased in favour of resorption and the rate of resorption is associated with the serum levels of thyroid hormones in hyperthyroidism [3]. Thyroid hormone exerts its effect on osteoblasts via nuclear receptors to stimulate osteoclastic bone resorption [4,5]; hyperthyroidism is...

Serum Osteocalcin Levels in Hyperthyroidism before and after Antithyroid Therapy

“…Our results point to the increase in osteoblastic activity in bone metabolism and thus we believe that the serum OC level is a good marker to detect the osteoblastic activity of bone metabolism in hyperthyroidism. There are similar results with our study showing high levels of OC as a marker pointing to the increase of the osteoblastic activity (Kobe et al 1999;Akalin et al 2002;Kısakol et al 2003). In our study group, all patients had clinical symptoms where as in Engler et al's study (1999), the subclinical hyperthyroid patients were studied and the same increase in bone activity was also found.…”

“…Recent investigations reveal that hyper secretion of thyroid hormones results in an increase in resorption and formation activity of bone metabolism (Siddiqi et al 1997;Isaia et al 2000;Akalin et al 2002;Kısakol et al 2003). In our study, we found elevated OC levels in hyperthyroid state, significantly higher than the control group.…”

Hypercalcaemia in a dog with primary hypothyroidism : clinical communication

“…In humans with adult-onset hypothyroidism serum concentrations of calcium and phosphorus are typically within normal limits 7 , whereas in congenital hypothyroidism up to 23 % of children exhibit hypercalcaemia with elevated concentrations of PTH and calcitriol 8 . Mild hypercalcaemia (up to 3.04 mmol/ ) has been reported in dogs with congenital hypothyroidism 4,5 , with untreated puppies continuing to show mildly elevated serum calcium levels during adulthood 4 .…”

Thyroid Disorders and Bone Mineral Homeostasis

“…Bone resorption markers, urinary pyridinoline and deoxypyridinoline, are increased 7-8 times more than in age and sex matched controls (Kraenzlin et al, 2008). Furthermore, hyperthyroid patients display a greater increase in urinary pyridinoline cross-links than that in serum markers of bone formation (osteocalcin, bone-specific alkaline phosphatase) (Akalin et al, 2002;Kisakol et al, 2003). Altogether, an increased bone turnover in these patients is in favor of osteoclastic bone resorption.…”

“…A higher BMD has been reported in postmenopausal women with TSH within the physiological range comparing to these with the low level of TSH (Baqi et al, 2010). Clinical observations show that patients with subclinical hyperthyroidism and normal circulating thyroid hormone levels display osteoporotic changes (De Menis et al, 1992; Kisakol et al, 2003). Strong correlation between serum TSH and bone status has been demonstrated in postmenopausal women (Bauer et al, 2001; Morris et al, 2007).…”