Physiology of Calcium metabolism:
Types & Causes:
- Primary hyperparathyroidism:
- Parathyroid adenoma (overall MC cause), MC site: Inferior parathyroid
- Parathyroid hyperplasia.
- Secondary hyperparathyroidism:
- Vitamin D deficiency.
- Tertiary hyperparathyroidism:
- Long standing CKD → Parathyroid hyperplasia → Adenoma.
- Hypercalcemia of malignancy
- Paraneoplastic syndrome due to PTHrP (PTH related peptide)
- MC-ly seen with squamous cell carcinoma of lung.
Primary hyperparathyroidism (PHPT)
- It is the MC cause of chronic hypercalcemia
- Pathophysiology: ↑PTH → ↑Serum calcium
- Clinical features:
- Primary hyperparathyroidism is mostly asymptomatic
- Clinical features of hypercalcemia may be seen:
- Bones: Bone pain, pathological fractures, Brown’s tumor, Osteitis fibrous cystica
- Stones: Recurrent/ multiple renal stones
- Abdominal groans: Colicky pain, Pancreatitis
- Psychiatric moans: Psychosis.
Radiological features of long-standing hyperparathyroidism:
- X-ray skull: Salt & pepper skull
- Subperiosteal resorption of radial side of 2nd & 3rd digits.
- Serum PTH: High
- Serum calcium: High
- Serum phosphorus: Low.
If getting the above biochemical picture, send the patient for an USG neck (BEST is Sestamibi scan):
- If only 1 gland is enlarged: Adenoma
- If all 4 glands are enlarged: Hyperplasia.
Surgery is preferred for:
- All symptomatic patients
- Asymptomatic patient with age <50 years, serum calcium 1 mg/dl above the baseline and/or features of osteoporosis/ renal stone.
- Adenoma: Remove only adenomatous gland
- Hyperplasia: Remove 3 & ½ glands. Remaining ½ gland is removed, minced into small pieces and inserted into brachioradialis of non-dominant hand/ SCM muscle.Advantage of this method: If there is a recurrence, we can remove the gland under local anesthesia as we already know the site where we have implanted.
- A thymectomy should be routinely undertaken for patients with MEN 1-associated PHPT or in secondary hyperparathyroidism.
Special note: Hungry bone syndrome after parathyroidectomy:
- Initial pathology was Hyperparathyroidism, stimulating both osteoblasts and osteoclasts
- After parathyroidectomy, the stimulation to osteoclasts go away first but osteoblasts remain activated for few weeks → In this time, ↑serum calcium is taken by bone → Resulting in hypocalcemia
- As bone takes more calcium in this period, this is known as “Hungry bone syndrome”.
All other asymptomatic patients should undergo medical management for correction of hypercalcemia:
- Diuretics (Loop diuretics → Furosemide)
- Bisphosphonate (inhibition of osteoclastic activity); Limitation: Delayed onset of action, takes 24-48 hours to show effect