Q&A Medicine>>>>>Endocrine and Metabolic Disorders
Question 9#

A 72-year-old woman presents with bone pain and tenderness in her lower extremities and left clavicle. Review of her chart reveals chronic bone marrow fibrosis with increased bone remodeling, in addition to several episodes of kidney stones (specifically calcium oxalate). Physical examination reveals tenderness to palpation on her lower legs and left midclavicle. Laboratory studies reveal elevated calcium, decreased phosphate, and elevated parathyroid hormone (PTH). X-ray reveals the following:

Which of the following is the diagnosis?

A. Paget disease of the bone
B. Osteomalacia
C. Osteoporosis
D. Osteitis fibrosa cystica

Correct Answer is D

Comment:

Osteitis fibrosa cystica. The patient in this question has hyperparathyroidism (elevated PTH) and is showing clinical symptoms for osteitis fibrosa cystica, a disease in which cystic bone spaces are filled with brown fibrous tissue. This disease is associated with hyperparathyroidism because PTH first acts on osteocytes and then on osteoclasts, causing calcium to be resorbed from the bone matrix and available in the blood stream (hypercalcemia). PTH also causes decreased phosphate reabsorption in the nephron, which causes decreased blood phosphate levels (hypophosphatemia). Hypercalciuria is yet another sign of hyperparathyroidism, which leads to the formation of calcium oxalate stones. The above figure shows osteosclerosis with greater density at the endplates (rugger jersey spine), which can be seen with hyperparathyroidism.

(A, C) Paget disease of the bone also causes bone pain and involves disorganized bone remodeling, but this disease usually causes misshapen bones and fractures and is typically localized to only a few bones in the body, in contrast with osteoporosis in which typically all the bones in the body are affected. Furthermore, laboratory studies are critical for nailing the diagnosis, since Paget disease of the bone and osteoporosis do not cause changes in calcium, phosphate, and PTH levels (although Paget disease is associated with increased alkaline phosphatase). (B) Osteomalacia involves defective bone mineralization due to vitamin D deficiency in adults, causing decreased calcium levels, which subsequently causes PTH to increase. With the increased secretion of PTH, serum phosphate levels decrease.