Disorders of the Parathyroid

Definition

Disorders of the parathyroid glands involve abnormalities in the secretion of parathyroid hormone (PTH), which regulates calcium and phosphate levels in the blood. The primary disorders include hyperparathyroidism and hypoparathyroidism.

Aetiology

The causes of parathyroid disorders vary based on the specific condition:

Primary Hyperparathyroidism: Caused by a benign tumour (adenoma) in one of the parathyroid glands, hyperplasia of multiple glands, or, rarely, a parathyroid carcinoma.
Secondary Hyperparathyroidism: Results from chronic kidney disease, vitamin D deficiency, or malabsorption syndromes leading to low calcium levels that stimulate overproduction of PTH.
Tertiary Hyperparathyroidism: Occurs after long-standing secondary hyperparathyroidism, particularly in patients with renal failure, where the glands become autonomously overactive.
Hypoparathyroidism: Can be caused by surgical removal or damage to the parathyroid glands, autoimmune destruction, or genetic disorders.

Pathophysiology

The pathophysiology of parathyroid disorders is linked to the role of PTH in calcium homeostasis:

Hyperparathyroidism: Excess PTH increases calcium release from bones, calcium reabsorption in the kidneys, and vitamin D-mediated absorption of calcium in the intestines, leading to hypercalcaemia.
Hypoparathyroidism: Deficiency of PTH reduces these processes, resulting in hypocalcaemia and hyperphosphataemia.

Risk Factors

Female gender (especially postmenopausal women)
Family history of parathyroid disorders
Chronic kidney disease
Neck surgery or radiation therapy
Vitamin D deficiency
Genetic mutations (e.g., MEN1, MEN2A, CASR gene mutations)

Signs and Symptoms

Symptoms of parathyroid disorders can vary depending on the specific condition:

Hyperparathyroidism:
- Hypercalcaemia: Fatigue, muscle weakness, depression, bone pain, polyuria, kidney stones, abdominal pain.
- Osteoporosis and fractures due to bone resorption.
Hypoparathyroidism:
- Hypocalcaemia: Muscle cramps, tetany, paraesthesia, seizures, cardiac arrhythmias.
- Chvostek's and Trousseau's signs: Neuromuscular irritability.

Investigations

Serum calcium and phosphate levels: Elevated in hyperparathyroidism, low in hypoparathyroidism.
Serum PTH levels: Elevated in hyperparathyroidism, low in hypoparathyroidism.
24-hour urinary calcium: To assess calcium excretion.
Bone densitometry (DEXA scan): To evaluate bone density and assess risk of fractures.
Imaging studies: Ultrasound or sestamibi scan to localise parathyroid adenomas or hyperplasia.
Genetic testing: For familial or hereditary cases of parathyroid disorders.

Management

Primary Care Management

Referral to endocrinologist: For diagnosis confirmation and management plan.
Monitoring: Regular follow-up for patients with mild primary hyperparathyroidism or hypoparathyroidism.
Calcium and vitamin D supplementation: For hypoparathyroidism to maintain normal calcium levels.
Education: Informing patients about the condition, importance of medication adherence, and recognising symptoms of calcium imbalances.

Specialist Management

Surgery: Parathyroidectomy for symptomatic primary hyperparathyroidism or parathyroid carcinoma.
Medical therapy:
- Calcimimetics (e.g., cinacalcet) for primary hyperparathyroidism when surgery is not an option.
- Phosphate binders and vitamin D analogues for secondary hyperparathyroidism in chronic kidney disease.
- Recombinant PTH (e.g., teriparatide) for severe hypoparathyroidism not controlled with calcium and vitamin D.
Management of complications: Addressing osteoporosis, kidney stones, and other complications of hypercalcaemia or hypocalcaemia.
Genetic counselling: For patients with hereditary parathyroid disorders.

Example Management for Parathyroid Disorders

A patient diagnosed with primary hyperparathyroidism presenting with hypercalcaemia and bone pain should be referred to an endocrinologist. Initial management includes ensuring adequate hydration, monitoring serum calcium and PTH levels, and considering surgical removal of the affected parathyroid gland(s). If surgery is not feasible, medical therapy with calcimimetics (e.g., cinacalcet) can be used to control calcium levels. The patient should be educated on the importance of follow-up and monitoring for potential complications such as kidney stones and osteoporosis.

References

NICE. (2024). Hyperparathyroidism (Primary): Diagnosis, Assessment and Initial Management. Retrieved from NICE
NHS. (2023). Parathyroid Disorders. Retrieved from NHS
British Thyroid Foundation. (2022). Parathyroid Disease. Retrieved from British Thyroid Foundation
Endocrine Society. (2021). Clinical Practice Guidelines for the Management of Primary Hyperparathyroidism. Retrieved from Endocrine Society