Which of the following diseases is not associated with low BMD?

• A. Osteoporosis
• B. Osteoarthritis
• C. Osteopetrosis
• D. Rheumatoid arthritis

Answer: (C)

Osteopetrosis is not associated with low bone mineral density (BMD), making it the correct choice in this scenario. Osteopetrosis is a rare bone disorder characterized by the abnormal density of bones due to defective osteoclasts, the cells responsible for bone resorption. As a result, the bones become abnormally dense and overly mineralized, which is in direct contrast to conditions like osteoporosis, where bone density is significantly reduced.

Osteoporosis is defined by low BMD and increased fracture risk, while rheumatoid arthritis can lead to localized bone loss due to inflammation and the presence of cytokines. Osteoarthritis, although primarily associated with joint degeneration, can also lead to changes in subchondral bone and may have a complex relationship with bone density; however, it typically does not lead to low BMD in the way that conditions like osteoporosis or rheumatoid arthritis can when they affect bone strength and density.

In summary, osteopetrosis is characterized by increased bone density and does not fit into the category of diseases that lead to low BMD.