Hyperparathyroidism is an increased parathyroid hormone (PTH) level in the blood.
Increased levels of the PTH lead to increased osteoclastic activity. The resultant bone resorption produces cortical thinning (subperiosteal resorption) and osteopaenia.
Primary: Increased Secretion of PTH unrelated to the plasma calcium concentration
Secondary: Increased Secretion of PTH secondary to hypocalcaemia
Tertiary: Autonomous PTH secretion following chronic secondary hyperparathyroidism