A 70-year woman comes to the office due to acute midthoracic back pain that started after a ground-level fall. The patient has also had weakness and weight loss for the past 2 months. Blood pressure is 150/70 mm Hg and pulse is 110/min. Examination shows sweaty palms and a fine hand tremor. Laboratory evaluation reveals normal hemoglobin, serum calcium, serum creatinine, and 25-hydroxyvitamin D levels. Serum thyrotropin (TSH) is undetectable. X-ray reveals a compression fracture of the T7 vertebra with diffuse demineralization of the bones. Which of the following is most likely responsible for the bone abnormalities in this patient?

Question

A 70-year woman comes to the office due to acute midthoracic back pain that started after a ground-level fall.  The patient has also had weakness and weight loss for the past 2 months.  Blood pressure is 150/70 mm Hg and pulse is 110/min.  Examination shows sweaty palms and a fine hand tremor.  Laboratory evaluation reveals normal hemoglobin, serum calcium, serum creatinine, and 25-hydroxyvitamin D levels.  Serum thyrotropin (TSH) is undetectable.  X-ray reveals a compression fracture of the T7 vertebra with diffuse demineralization of the bones.  Which of the following is most likely responsible for the bone abnormalities in this patient?

Quizplus · Accepted Answer

11ec160b_3cad_d871_9249_a90ea38cc5da_MD0001_00 This patient has hyperthyroidism, presenting with weight loss, tremor, tachycardia, and a suppressed TSH level. In addition, she has an acute vertebral compression fracture and diffuse bone mineral loss consistent with osteoporosis. Hyperthyroidism causes increased bone turnover with net bone loss. The bone loss in hyperthyroidism is driven by triiodothyronine (T3), the more active form of thyroid hormone that is generated primarily by deiodination of thyroxine (T4) in peripheral tissues. T3 stimulates osteoclast differentiation, increased bone resorption, and release of calcium. As calcium is released from the bones into the circulation, it suppresses parathyroid hormone (PTH) secretion, which leads to decreased reabsorption of calcium in the renal tubules and gut. This maintains normal blood calcium levels as bone mineralization is progressively depleted. (Choice A) Thyroid hormone stimulates (not inhibits) osteoblast differentiation and activity, leading to increased formation of new bone. However, in the hyperthyroid state, this effect is outweighed by a greater increase in bone loss. (Choice B) Mineralization of bone matrix is regulated directly by local concentrations of calcium and inorganic phosphate and indirectly by multiple endocrine and paracrine factors (eg, PTH, vitamin D). Although vitamin D deficiency can cause osteomalacia due to impaired mineralization, thyroid hormone has only a minor effect on this process. (Choice C) Calcitonin is released by the parafollicular cells of the thyroid. It inhibits osteoclast activity, leading to decreased (not increased) bone resorption. Calcitonin is regulated primarily by circulating calcium levels, not thyroid hormone. (Choice E) In addition to causing lytic bone lesions, multiple myeloma causes diffuse bone loss due to interleukin-1-induced uncoupling of bone resorption and formation (ie, increased osteoclast activity without a restorative osteoblast action). Educational objective: Hyperthyroidism causes increased bone turnover with net bone loss, potentially leading to osteoporosis. The bone loss is driven by triiodothyronine, which stimulates osteoclast differentiation, increased bone resorption, and release of calcium.

A 70-Year Woman Comes to the Office Due to Acute