*Study on the Impact of Diseases and Medical Treatments on Bone Mineral Density DOI: http://dx.doi.org/10.5772/intechopen.110318*

**Hyperparathyroidism:** It refers to an endocrine disorder characterized by an abnormal elevation of PTH production by parathyroid glands. This causes hypercalcemia by inducing a loss of calcium from the bones and an excessive gain of calcium in the blood. For that reason, hyperparathyroidism induces serious renal and skeletal problems [58]. Due to calcium deficiency in the bone, hyperparathyroidism has been shown to be associated with increased osteoporosis risk and significantly reduced BMD [58].

## **4.2 Medical treatment-associated bone deterioration**

**Glucocorticoids:** They are a sort of drugs composed of primary stress hormones that regulate various physiological processes [59]. They are used as anti-inflammatory, antiallergic, and immunosuppressive to treat different disease types and more often inflammatory skin disorders such like allergic contact eczema and toxic-irritative eczema [60, 61]. Given its nature, an excess of glucocorticoids leads to reduced calcium intestinal absorption and calcium renal excretion and sex steroid level decrease, which affects bone remodeling by stimulating bone repression and inhibiting formation, leading to bone loss, low BMD, and elevated risk of fracture [62].

**Radiotherapy:** It consists of using X-rays or subatomic particles directly on tumor cells in curative and palliative settings [63]. Thanks to this procedure, cancer cells shrink, and the local cancer recurrence is reduced [64]. However, RT noticeably affects bone quality, leading to fragility in the zones surrounding the treated tumor area. Indeed, RT decreases cellularity; affects bone-forming cell differentiation, proliferation, and production; and stimulates bone-resorbing cell differentiation using low radiation doses [65]. This explains the significant decrease in BMD value in the area treated with RT as noticed in [66] study investigating RT effect on lumbar vertebrae in women with cervical cancer [66].

**Chemotherapy:** It involves the use of chemical agents capable of destroying cancer cells by either affecting their macromolecular synthesis by interfering with their DNA or affecting the appropriate functioning of the preformed molecule. This limits cell proliferation and consequently their invasion. Besides their good efficacy on cancer cells, chemotherapy has toxic effects on normal cells, including bone cells, which affects bone quality [67]. Ovarian failure and negative and positive effects on osteoblastogenesis and osteoclastogenesis, respectively, due to chemotherapy induce bone loss [68, 69] in addition to loss of bone mineral density as found in (Bone mineral density change during adjuvant chemotherapy in pediatric osteosarcoma), where children under chemotherapy have shown a decrease of BMD in lumbar spine and femoral neck especially at the end of the therapy [70].

**Aromatase Inhibitors (AIs):** These are medications used for the treatment of breast cancer, notably estrogen receptor positive, by blocking estrogen synthesis [71]. Because of their action on estrogen, women undergoing AI develop osteoporosis, which induces bone fractures and leads to up to 2.6% loss of BMD per year in lumbar spine [69].

**Androgen deprivation therapy (ADT):** As well as AIs, ADT is also a treatment controlling sex hormone synthesis, more precisely suppressing or blocking the production or action of male hormones, notably testosterone. Given the important role of testosterone already mentioned, ADT induces osteoporosis. Its effect is much higher than that of AIs as it has been found that ADT causes 4.6% loss of BMD per year in lumbar spine, while AIs induce approximatively 2.6% of BMD decrease [69].

**Bone marrow transplant:** It is a procedure in which heathy hematopoietic stem cells are administrated into the patient to replace the depleted bone marrow with dysfunctional cells that have been destroyed by treatments such as radiation or high doses of chemotherapy. This permits to supplement bone marrow functioning and to destroy treated malignant tumor cells. The healthy stem cells come from the bone marrow of the patient or from a donor [72]. The hematopoietic cell transplantation has also been identified as one of the medical procedures causing reduced BMD. The major causes of this loss are low sexual hormones notably estrogen and testosterone, secondary hyperparathyroidism due to reduced calcium concentration, and posttransplant steroid therapy—50–60% of patients undergoing this therapy undergo bone loss [73]. In the work of [74], authors have noticed a significant loss in BMD value in the hip, reaching 4.2% for men and women under observation over 1 year of treatment.
