Mandy is a 16-year-old competitive figure skater who practices several hours a day with her coach at the skating arena. Because of her extremely active lifestyle and restricted diet to maintain her athletic physique, she experiences ongoing amenorrhea

Question

One day during practice, she landed a jump and fell to the ice in pain. Her left foot swelled up almost immediately, making it difficult for her coach to remove the skate. At the hospital, radiographs revealed a fracture of the fifth metatarsal bone and general radiolucency of all the bones in her foot. A follow-up DXA revealed a bone mass of 2.7 standard deviations below mean.

What is the etiology of Mandy's premature osteoporosis, and how her condition is thought to contribute to a decrease in bone density?

Knowing what you do about bone mineralization, why does a deficiency of estrogen in women lead to osteoporotic change?

Osteoporosis and osteomalacia both involve abnormal bone mineralization. What are the general macroscopic differences of these two conditions?

Answer 1

Mandy is likely demonstrating the effects of the female athletic triad. Disordered eating and intensive exercise in some athletes reduce fat stores and the fat-to-muscle ratio. The result is a decrease in estrogen production by the ovaries with amenorrhea. The reduction in circulating estrogen, coupled with an insufficient intake of vitamin D and calcium, accelerates bone resorption and the formation of osteoporosis.

Estrogen deficiency contributes to the development of osteoporosis in a number of ways. Lowered levels of estrogen encourage an increase in cytokine production that stimulates the proliferation of osteoclast precursors. Furthermore, when estrogen is low, the differentiation of osteoclasts becomes unregulated; osteoclast precursors are more responsive to the RANK ligand, and osteoclastic proliferation occurs. The result is a condition of bone resorption that occurs at a rate that cannot be matched by a compensatory increase in osteoblastic activity.

Osteoporosis is a disease characterized by a decline in bone mass. Osteoporotic bone is porous and brittle with a decreased amount of trabeculae and cortical volume. Osteomalacia, in contrast, is a disease characterized by the undermineralization of bone. Bone tissue exhibiting osteomalacia is soft and weak due to the lack of mineralization. Total bone mass, however, is unchanged.