Many people only have non-specific symptoms.Common manifestations of hypercalcemia include weakness and fatigue, depression, bone pain, muscle soreness (myalgias), decreased appetite, feelings of nausea and vomiting, constipation, pancreatitis, polyuria, polydipsia, cognitive impairment, kidney stones (), vertigo and osteopenia or osteoporosis. A history of acquired racquet nails (brachyonychia) may be indicative of bone resorption. Radiographically, hyperparathyroidism has a pathognomic finding of rugger jersey spine. Parathyroid adenomas are very rarely detectable on clinical examination. Surgical removal of a parathyroid tumor eliminates the symptoms in most patients.In secondary hyperparathyroidism due to lack of Vitamin D absorption, the parathyroid gland is behaving normally; clinical problems are due to bone resorption and manifest as bone syndromes such as rickets, osteomalacia, and renal osteodystrophy. Causes
Radiation exposure increases the risk of primary hyperparathyroidism. A number of genetic conditions including multiple endocrine neoplasia syndromes also increase the risk. Parathyroid adenomas have been linked with DDT although a causal link has not yet been established. Mechanism
Normal parathyroid glands measure the ionized calcium (Ca2+) concentration in the blood and secrete parathyroid hormone accordingly; if the ionized calcium rises above normal, the secretion of PTH is decreased, whereas when the Ca2+ level falls, parathyroid hormone secretion is increased.Secondary hyperparathyroidism occurs if the calcium level is abnormally low. The normal glands respond by secreting parathyroid hormone at a persistently high rate. This typically occurs when the 1,25 dihydroxyvitamin D3 levels in the blood are low and  hypocalcemia is present.
A process is a series or set of activities that interact to produce a result; it may occur once-only or be recurrent or periodic. Things called a process include:

Business and management
Business process, activities that produce a specific service or product for customers
Business process modeling, activity of representing processes of an enterprise in order to deliver improvements
Manufacturing process management, a collection of technologies and methods used to define how products are to be manufactured.