In osteoporosis, this balance of bone remodeling is disturbed (figure 2b-f). Osteopenia is a general term for an abnormally low bone mass and it is often caused by primary osteoporosis. Primary osteoporosis is classified as being either A. postmenopausal (Type 1), B. aging related (Type 2) or C. idiopathic (younger men and women). Secondary causes of osteoporosis include

       Cushing's Syndrome (or more commonly the use of oral corticosteroids), hyperthyroidism (or oral thyroid medication), hypogonadism ( in men), immobilization, chronic use of heparin, and osteogenesis imperfecta. Other causes for osteopenia include primary hyperparathyroidism, osteomalacia, myeloma, mastocytosis, and renal osteodystrophy.