Excessive secretion of parathyroid hormone (PTH) – normally controlled by calcium levels  common cause of hypercalcaemia. Relatively common. F>M.

80% due to parathyroid adenoma.
Secondary may be due to malabsorption syndromes, chronic renal failure and rickets.

Clinical features:
50% are asymptomatic.
Mnemonic – “Painful bones, renal stones, abdominal groans and psychic moans”
Usually present with – thirst, polydipsia, polyuria, abdominal pain, constipation, vomiting, weight loss, bone pain and tenderness, muscle fatigue (painless proximal muscle weakness with normal enzymes), altered mental states.
Joints are stiff after rest and have limited range of motion – can be sudden or gradual onset – polyarticular – most commonly knees - less commonly spine, hands, feet, wrists, elbow and ankles. CPPD deposition/pseudogout more common (may affect foot joints and achilles tendons).
X-ray – subperiosteal bone resorption (hands, wrists and feet – especially distal phalanges); subchondral bone resorption; bone resorption at entheses (eg calcaneus); osteoporosis

Medical – reduced calcium intake; oral phosphate; calcimimetics (new class of drugs that interfere with PTH production)
Surgical - removal of abnormal parathyroid tissue

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