Table 1

Brief overview of hyperparathyroidism

Syndrome	Primary hyperparathyroidism	Secondary hyperparathyroidism*	Tertiary hyperparathyroidism
Definition	Autonomous PTH oversecretion from abnormal parathyroid gland(s)	Pathophysiological PTH oversecretion in response to a chronic stimulus that is usually extracellular hypocalcaemia	Emergence of autonomous PTH oversecretion (neoplastic transformation) from secondary parathyroid hyperplasia usually occurring in the setting of long-standing CKD and after renal transplant
Clinical manifestations	Often asymptomatic; more symptomatic† in malignant HPT	May be symptomatic†, especially in patients with longstanding chronic kidney disease	May be symptomatic†; often refractory to medical therapy
Biochemistry	Mild hypercalcaemia with elevated PTH levels; more severe findings in malignant HPT	Normocalcemia or hypocalcaemia with elevated PTH levels; in patients with CKD: hyperphosphatemia, decreased 1,25-(OH)2D3	Hypercalcaemia and elevated PTH levels
Radiology	Single-gland parathyroid disease (80–85%) or multigland disease (10–15%)	Multigland parathyroid disease	Multigland parathyroid disease
Pathology	Parathyroid adenoma (80–85%), hyperplasia (10–15%) and/or carcinoma (<1–5%)	Parathyroid hyperplasia	Autonomous nodular proliferation (often adenoma, rarely carcinoma) in a background of parathyroid hyperplasia
Treatment	Surgery	Generally medical therapy, although surgery may be indicated in some patients with chronic kidney disease	Often surgery, given resistance to medical therapy

*Secondary causes of hyperparathyroidism include chronic kidney disease (most classic), vitamin D deficiency and calcium malabsorption.
†Signs and symptoms include bone pain, osteoporosis, kidney stones and neuropsychiatric manifestations. Additionally, patients with hyperparathyroidism due to chronic kidney disease may experience pruritus and calcification of soft tissues and vessels.
CKD, chronic kidney disease; HPT, hyperparathyroidism; PTH, parathyroid hormone.