Hyperparathyroidism
NICE guideline [NG132] Hyperparathyroidism (primary): diagnosis, assessment and initial management. Published: May 2019.
Overview Table
| Type | Definition | Most common cause |
|---|---|---|
| Primary hyperparathyroidism | Primary overactive parathyroid gland | Parathyroid adenoma |
| Secondary hyperparathyroidism | Secondary overactive parathyroid gland | CKD |
| Tertiary hyperparathyroidism | Autonomous PTH secretion secondary to untreated secondary hyperparathyroidism | Untreated secondary hyperparathyroidism |
Laboratory findings:
| Condition | Calcium | Phosphate | PTH | ALP |
|---|---|---|---|---|
| Primary hyperparathyroidism | ↑ | ↓ | ↑ / – | ↑ |
| Secondary hyperparathyroidism | ↓ | Varies based on cause:
|
↑ | |
| Tertiary hyperparathyroidism | ↑ | ↑ | ↑↑ | |
| Vitamin D deficiency | ↓ | ↓ | ↑ |
Primary Hyperparathyroidism
Definition
Primary hyperparathyroidism is defined as an endocrine disorder in which one or more of the parathyroid glands autonomously produce excessive amounts of PTH, which disrupts normal calcium and phosphate metabolism.
Epideimology
Primary hyperparathyroidism is the most common cause of hypercalcemia and should be considered in any person with an elevated serum calcium level. [Ref]
Aetiology
The majority of cases are sporadic: [Ref]
- Single parathyroid adenoma (~80-85% cases)
- 4-gland parathyroid hyperplasia (10-15% cases)
- Parathyroid carcinoma (<1% cases)
10-15% cases are due to hereditary syndromes: [Ref]
- MEN syndrome types 1 and 2A
Clinical Features
Most patients are asymptomatic. [Ref]
The primary manifestation of primary hyperparathyroidism is: [Ref]
- Hypercalcaemia (renal stones, painful bones, abdominal groans and psychic moans)
- Renal stones: renal / ureteric stones, polyuria and polydipsia (from nephrogenic diabetes insipidus)
- Painful bones: bone / muscle / joint pain, pseudogout, muscle weakness
- Abdominal groans: abdominal pain, constipation, anorexia, N&V, pancreatitis
- Psychic moans: depression, fatigue, confusion
- End-organ disease
- Kidney stones
- Osteoporosis
- Fragility fractures
Investigation and Diagnosis
Albumin-adjusted serum calcium should be measured (not ionised calcium)
Biochemical changes in primary hyperparathyroidism:
- ↑ / Normal PTH
- ↑ Calcium
- ↓ Phosphate
- ↑ ALP
Rationising the biochemical changes:
- Actions of PTH
- ↑ Serum calcium (via ↑ bone resorption, ↑ renal calcium reabsorption, ↑ intestinal calcium absorption)
- ↓ Serum phosphate (via ↑ renal phosphate excretion)
- ALP would be raised due to increased bone turnover (osteoblasts produce ALP as a marker of bone formation)
In primary hyperparathyroidism, the initiating event is raised PTH, which results in the subsequent biochemical changes.
NICE recommends first measuring albumin-adjusted serum calcium if primary hyperparathyroidism is suspected, and only to measure PTH level if calcium is elevated.
However, usually all calcium, phosphate, PTH and ALP would be ordered together as a metabolic bone panel or bone profile. And in exams, one would definitely be expected to interpret all 4 above-listed parameters.
Post-Diagnosis Assessment
Post-diagnosis of primary hyperparathyroidism, NICE recommends assessing:
- Vitamin D level
- eGFR or serum creatinine
- DEXA
- Ultrasound of the renal tract
If ALP is raised, it’s important to order an LFT to exclude hepatic causes of raised ALP. Be aware that a raised ALP can be secondary to 1) bone problems 2) liver problems and 3) pregnancy.
Familial Hypocalciuric Hypercalcaemia (FHH)
FHH is an important differential of primary hyperparathyroidism that also presents with similar biochemical changes (↑ calcium ↓ phosphate ↑ PTH)
Main distinguishing factors are:
- ↓ Urinary calcium excretion (<0.01 Ca: Cr clearance ratio)
- Urinary calcium excretion is high in primary hyperparathyroidism
- +ve Family history (FHH is autosomal dominant – due to an inactivating mutation in the calcium-sensing receptor)
- Usually asymptomatic
- Biochemical changes are mild
Importantly, FHH is managed very differently from primary hyperparathyroidism:
- It is a benign lifelong condition
- Surgery is not indicated and will provide no benefit
- Parathyroidectomy will NOT normalise calcium levels
Management
Choice of definitive management:
- 1st line: surgery
- 2nd line: medical therapy
Surgical Management
Surgery should be offered in ANY of the following:
- Symptomatic hypercalcaemia (e.g. thirst, frequent or excessive urination, constipation)
- Very high calcium levels (albumin-adjusted serum calcium ≥2.85)
- Any end-organ disease
- Renal stone
- Osteoporosis
- Fragility fractures
Choice of Surgical Approach
Offer pre-operative ultrasound to guide the surgical approach.
Choices depend on ultrasound findings:
- Single adenoma identified → choice of focused parathyroidectomy or 4-gland exploration (involves identifying all parathyroid glands and treating abnormal tissue)
- All other patients (inc. inconclusive imaging, suspected multiglandular disease, or hereditary/refractory cases ) → 4-gland exploration
- Surgical approaches:
- Subtotal parathyroidectomy (esp. if all 4 glands are hyperplastic) OR
- Total parathyroidectomy
- Surgical approaches:
Follow-Up After Surgery
Measure albumin-adjusted serum calcium and PTH before discharge.
Long-term monitoring involves measuring albumin-adjusted serum calcium:
- If it falls within the reference range 3-6 months after surgery = successful surgery
Medical Management
Cinacalcet (CaSR agonist) should only be considered if:
- Surgery is inappropriate (unsuccessful / contraindicated / declined by patients), and
- Symptomatic hypercalcaemia (≥2.85 mmol/L) / asymptmatic hypercalcaemia (≥3 mmol/L)
Bisphosphonates should NOT be offered to manage hypercalcaemia in primary hyperparathyroidism.
It should only be offered to reduce the risk of fracture. Refer to this article.
Secondary Hyperparathyroidism
Definition
Secondary hyperparathyroidism is defined as a physiological increase in PTH secretion in response to chronic disturbances in mineral metabolism.
I.e. the parathyroid gland is not secreting PTH autonomously, it is driven by an underlying cause (thus secondary).
Aetiology
CKD is the most common cause [Ref]
- The main trigger of excess PTH secretion is hypocalcaemia (CKD leads to ↓ 1,25-dihydroxyvitamin D synthesis, thus hypocalcaemia)
- Hyperphosphataemia from CKD also triggers the PTH secretion
Other causes
- Generally causes of hypocalcaemia (triggers compensatory PTH secretion)
- Vitamin D deficiency
- Less commonly: chronic malabsorption, dietary calcium deficiency
In secondary hyperparathyroidism, the initiating event is hypocalcaemia and/or hyperphosphataemia (often secondary to CKD), which causes the subsequent raised PTH as compensation.
Investigation and Diagnosis
Biochemical changes in secondary hyperparathyroidism: [Ref]
- ↑ PTH
- ↓ Calcium
- ↑ ALP
- Phosphate (depends on underlying cause)
- CKD: ↑ phosphate
- Non-CKD causes (i.e., vitamin D deficiency): low or normal phosphate
X-ray findings in secondary hyperparathyroidism: [Ref]
- Subperiosteal bone resorption – hallmark features (commonly seen in the radial aspect of middle phalanges)
- Osteitis fibrosa cystica (cystic bone lesions called brown tumour – caused by bone resorption and fibrous tissue proliferation)
- “Rugger jersey spine” (alternating sclerotic and lucent bands in the vertebral bodies)
- Pathological features
Management
The exact management is complicated, and there is a lack of universally accepted clinical guidelines. Currently, no NICE guideline is dedicated to the management of secondary hyperparathyroidism.
Therefore, the principles of management (that are appropriate for medical students) are summarised below.
Initial management: [Ref1][Ref2]
- Optimise CKD management, treat any reversible causes of CKD
- Treat hyperphosphataemia
- Dietary phosphate restriction
- Phosphate binders (non-calcium binders are preferred to minimise risk of hypercalcaemia)
- Treat vitamin D deficiency
If the above failed: consider cinacalcet (CaSR agonist) [Ref1][Ref2]
Last resort: parathyroidectomy (reserved for medically refractory cases / severe complications) [Ref1][Ref2]
Tertiary Hyperparathyroidism
Definition
Tertiary hyperparathyroidism is defined as the autonomous, excessive secretion of PTH by hyperplastic parathyroid glands that develops after longstanding secondary hyperparathyroidism.
Aetiology
Prolonged, untreated secondary hyperparathyroidism
Investigation and Diagnosis
Biochemical changes in secondary hyperparathyroidism: [Ref]
- ↑ ↑ PTH (markedly raised)
- ↑ Calcium
- ↑ Phosphate
- ↑ ALP
Everything is high in tertiary hyperparathyroidism. But not in primary and secondary hyperparathyroidism.
Long-standing secondary hyperparathyroidism causes autonomous hyperplasia of the parathyroid glands, which leads to excessive and unregulated PTH secretion, independent of serum calcium levels.
Management
The exact management is complicated, and there is a lack of universally accepted clinical guidelines. Currently, no NICE guideline is dedicated to the management of secondary hyperparathyroidism.
Therefore, the principles of management (that are appropriate for medical students) are summarised below.
Surgical management (subtotal parathyroidectomy / total parathyroidectomy with autotransplantation of parathyroid tissue) is the definitive management. [Ref]
Medical management: [Ref]
- Cinacalcet
- Phosphate binders