Ans. (d) 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 figure shows osteosclerosis with greater density at the endplates (rugger jersey spine), which can be seen with hyperparathyroidism.Image source- style="font-family: Times New Roman, Times, serif">