hypercalcemia
Hypercalcemia means too much calcium in the blood. Since calcium calms down excitable tissues like nerves and muscle, having too much makes the body sluggish, summed up by the old clinical rhyme: stones, bones, abdominal groans, and psychiatric moans.
Those words map to real symptoms: kidney stones from excess calcium in urine, bone pain from the disease driving it, constipation and nausea from a slowed gut, and confusion, fatigue, or depression from effects on the brain. By far the two most common causes are an overactive parathyroid gland (primary hyperparathyroidism) and cancer, which can raise calcium by spreading to bone or by secreting a PTH-like protein. Excess vitamin D and some medications can also be culprits.
Mild hypercalcemia may cause no symptoms and is often found by chance on blood tests. Severe or rapidly rising calcium is a medical emergency that can disturb heart rhythm and cause coma, treated urgently with intravenous fluids and drugs that block bone resorption. Finding the cause hinges on whether PTH is high (pointing to the parathyroids) or suppressed (pointing elsewhere, often cancer).
An older man with recurrent kidney stones and vague fatigue is found to have high calcium and high PTH, leading to a diagnosis of primary hyperparathyroidism.
Stones plus high PTH point straight to the parathyroids.
The single most useful first step in working up hypercalcemia is checking PTH: if PTH is high or inappropriately normal, the parathyroids are the likely culprit; if it is suppressed, look hard for cancer or vitamin D excess.