Hyperparathyroidism Diagnosis and Management

Primary Hyperparathyroidism

• Single parathyroid adenoma accounts for approximately 80% of primary hyperparathyroidism cases, making it the most common etiology 1
• The American College of Endocrinology recommends measuring serum calcium (corrected for albumin) and intact PTH simultaneously to establish the diagnosis 2
• The combination of hypercalcemia with elevated or inappropriately normal PTH levels is diagnostic of primary hyperparathyroidism 2, 1
• Multigland disease (hyperplasia) affects 15-20% of patients with primary hyperparathyroidism 1
• Parathyroid carcinoma is rare, occurring in less than 1% of cases 1
• Serum phosphate is typically low or low-normal 2
• Most patients demonstrate hypercalciuria (>250-300 mg/day) due to increased filtered calcium load from hypercalcemia 2, 1

Secondary Hyperparathyroidism

• Secondary hyperparathyroidism is characterized by elevated PTH in response to chronic hypocalcemia, hyperphosphatemia, or vitamin D deficiency, with normal or low serum calcium levels 3, 4
• SHPT represents a compensatory physiologic response where increased PTH production attempts to correct calcium homeostasis but fails due to underlying organ dysfunction or reduced calcium availability 3
• The three primary drivers are: hyperphosphatemia, hypocalcemia, and vitamin D deficiency 4
• Chronic kidney disease is the most common cause, as declining renal function leads to phosphate retention, decreased calcitriol production, and impaired calcium absorption 3, 4
• Normal or low serum calcium with elevated PTH is the hallmark finding 2, 4
• Hyperphosphatemia is defined as serum phosphorus >4.6 mg/dL in CKD stages 3-4, or >5.5 mg/dL in stage 5 4
• Hypocalcemia is defined as corrected serum calcium <8.4 mg/dL 4
• Vitamin D deficiency is defined as 25(OH)D <30 ng/mL 4
• Alkaline phosphatase is often elevated, suggesting high bone turnover 4

Tertiary Hyperparathyroidism

• Tertiary hyperparathyroidism is marked by hypercalcemia with elevated PTH, representing autonomous PTH hypersecretion after longstanding secondary hyperparathyroidism 1, 3
• The parathyroid glands become autonomously hypersecreting after prolonged stimulation, losing their normal feedback regulation 3
• Most commonly encountered following kidney transplantation in patients with long-standing chronic kidney disease 3, 1
• Unlike secondary hyperparathyroidism, PTH remains elevated despite rising serum calcium levels, manifesting as hypercalcemic hyperparathyroidism 3
• Typically involves multigland disease (parathyroid hyperplasia) 1

Diagnostic Distinctions

• The following table summarizes key diagnostic distinctions between primary and secondary hyperparathyroidism:

2, 1, 4

• Vitamin D deficiency can complicate interpretation of PTH levels in both conditions and must be assessed 2
• Different PTH assay generations measure different PTH fragments and can yield significantly different values, requiring use of assay-specific reference ranges 5, 2

Management of Primary and Secondary Hyperparathyroidism

Etiology of Secondary Hyperparathyroidism

• Malabsorption syndromes and vitamin D deficiency are additional causes of secondary hyperparathyroidism beyond chronic kidney disease. 6

Indications for Surgical Intervention in Secondary Hyperparathyroidism

• Surgical excision is recommended for medically refractory secondary hyperparathyroidism when pharmacologic therapy fails to control PTH and mineral abnormalities. 6

Imaging Strategy for Secondary Hyperparathyroidism

• Because secondary hyperparathyroidism usually involves multigland hyperplasia, imaging should be performed to identify all eutopic and ectopic (or supernumerary) parathyroid glands. 6

Tertiary Hyperparathyroidism

• Tertiary hyperparathyroidism most commonly develops after kidney transplantation in patients with long‑standing chronic kidney disease. 6
• In tertiary hyperparathyroidism, PTH remains elevated despite rising serum calcium levels, reflecting autonomous secretion. 6
• Surgical excision is advised for medically refractory tertiary hyperparathyroidism. 6

Primary Hyperparathyroidism – Curative Therapy

• Parathyroidectomy is the only curative treatment for primary hyperparathyroidism. 7

Primary Hyperparathyroidism – Minimally Invasive Parathyroidectomy (MIP)

• Since the majority of patients have a single adenoma, minimally invasive parathyroidectomy provides shorter operative times, faster recovery, and lower peri‑operative costs compared with more extensive surgery. 7

Primary Hyperparathyroidism – Bilateral Neck Exploration (BNE)

• Bilateral neck exploration remains necessary when pre‑operative imaging is discordant, non‑localizing, or when there is strong suspicion for multigland disease. 7

Role of Imaging in Primary Hyperparathyroidism Diagnosis

• Imaging does not confirm or exclude the diagnosis of primary hyperparathyroidism; it is used solely for lesion localization after a biochemical diagnosis is established. 7

Imaging in Re‑operative Primary Hyperparathyroidism

• In the re‑operative setting, pre‑operative imaging is essential to localize the target parathyroid lesion before repeat surgery. 7

Critical Pitfall – Misuse of Imaging

• Imaging should never be employed to confirm or exclude hyperparathyroidism, as diagnosis is based purely on biochemical criteria. 7

Post‑bariatric Secondary Hyperparathyroidism and PTH Assay Variability

Epidemiology

• Approximately 63 % of individuals develop secondary hyperparathyroidism within five years after bariatric surgery, reflecting the high prevalence of calcium‑vitamin D malabsorption in this population. 8

Laboratory Considerations

• Different generations of parathyroid hormone (PTH) assays detect varying PTH fragments; consequently, measured PTH values can differ markedly between assays, necessitating the use of assay‑specific reference ranges for accurate interpretation. 8