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Parathyroid Disorders (Hypoparathyroidism (Aetiology (Surgical removal -…
Parathyroid Disorders
Hypoparathyroidism
= Not enough parathyroid hormone
Epidemiology
Hypocalcaemia is found in 88% of intensive care patients
Aetiology
Surgical removal - secondary hypoparathyroidism
Magnesium deficiency
Congenital
Vitamin D deficiency - results in less calcium absorption. Causes of this are malabsorption and anti-epileptic drugs
Autoimmune destruction of parathyroid glands - primary hypoparathyroidism
Pseudohypoparathyroidism
Short 4th and 5th metacarpals
Bloods show low calcium, high PTH, low phosphate
Caused by a mutation in the G protein which is coupled to the PTH receptor
Treat as normal hypoparathyroidism
Resistance to PTH
Symptoms
Symptoms of hypocalcaemia: Confusion, muscle spasms and cramps, parathesia, hallucinations, Carpopedal spasm, seizure, anxiety, wheeze, dermatitis
Investigations
Test for parathyroid autoantibodies
25-hydroxyvitamin D serum level will be low in vitamin D deficiency
Bloods show low PTH, low calcium, high phosphate
Pseudopseudohypoparathyroidism
= The morphological features of pseudohypoparathyroidism but with normal biochemistry
Normal PTH, normal calcium, normal phosphate
Genetic
Treatment
Calcitriol (active vitamin D) - increases GI and kidney absorption of calcium
Synthetic parathyroid hormone
Calcium supplement
Hyperparathyroidism
= Too much parathyroid hormone
Aetiology
20% of cases are caused by parathyroid hyperplasia
<0.5% are caused by parathyroid carcinoma
80% of cases are caused by a solitary parathyroid adenoma
Pathophysiology
Excess PTH production causes hypercalcaemia
Symptoms
Symptoms of hypercalcaemia: weakness, fatigue, depression, thirst, stones
Hypertension
Bone resorption causes pain, fracture, osteoporosis
Most patients are asymptomatic
Investigations
Secondary hyperparathyroidism
will show: ↑PTH, ↓Ca2+, ↑Phosphate. Caused by vitamin D deficiency + CKD. Excess PTH is caused by hypocalcaemia
Tertiary hyperparathyroidism
will show: ↑everything. Progression of secondary. Glands act autonomously having undergone hyperplastic or adenomatous change, resulting in excess PTH secretion
Primary hyperparathyroidism
will show: ↑ PTH, ↑ Ca2+, ↓Phosphate
DEXA scan for osteoporosis
Increased 24 hour urinary calcium excretion - will be high in hypercalcaemia.
MRI or CT
Treatment
Bisphosphonates to prevent bone resorption
Surgery on tumours
IV fluid
Surgery to remove parathyroid glands
Treat underlying cause
Side Note
Hypercalcaemia can also be caused by malignancy: squamous cell lung cancer, breast and renal carcinomas
PTH is mimicked, raising Ca2+ levels
Cannot detect PTH as tumour doesn't secrete PTH itself.
Increased alkaline phosphatase
Parathyroid Physiology
Anatomy
Parathyroid hormone is secreted from 4 parathyroid glands
The parathyroid glands lie posterior to the thyroid gland
Action of Parathyroid Hormone
Activates 1,25-dihydroxy vitamin D in the kidney
Increases calcium reabsorption in the kidney
Increases intestinal calcium absorption
Increases phosphate excretion in the kidney
Increases bone resorption by osteoclasts
All these actions serve to increase plasma Ca2+
Function of Parathyroid Hormone
PTH is released in response to decreased plasma levels of Ca2+
Decrease in plasma Ca2+ is detected by receptors on the plasma membrane of parathyroid glands
PTH is secreted from chief cells of the parathyroid glands
Calcium
Vitamin D > 25-hydroxyl vitamin D > 1-25-hydroxyvitamin D (calcitriol)
Calcitriol increases Ca2+ and phosphate absorption in the gut and reabsorption in the kidney. It also enhances bone turnover by increasing the no. of osteoclasts. Inhibits PTH release
Calcitriol is the active form of vitamin D and it is released in low plasma Ca2+ and phosphate
Calcitonin is released from C cells in the thyroid and it decreases plasma Ca2+ and phosphate
40% of calcium is ionised, the rest is bound to albumin
Calcium Homeostasis
Physiology
Calcium balance is controlled by PTH and calcitonin
99% of calcium is stored in bone as calcium phosphate
Hypocalcaemia
Aetiology
Vitamin D deficiency - low phosphate
Osteomalacia - low phosphate
Acute pancreatitis - low phosphate
CKD - high phosphate
Hypoparathyroidism - high phosphate
Symptoms
Anxiety
Seizures
Peripheral paraesthesia
Increased muscle tone
Spasms
Investigations
ECG shows long QT interval
Serum Ca2+
Treatment
Mild: Adcal
Severe: calcium gluconate
Hypercalcaemia
Aetiology
90% is caused by primary hyperparathyroidism or cancer
Symptoms
Nausea and vomiting
Constipation and indigestion
Renal stones
Fatigue
Painful bones
Psychosis
Investigations
PTH level - high in hyperparathyroidism, low in cancer
U&E to assess renal damage
Take corrected calcium level - mild increase in hyperparathyroidism, severe increase in cancer
X-ray
Treatment
Bisphosphonates - encourages apoptosis of osteoclasts so there is less bone breakdown
Saline to dilute calcium levels
Hypercalcaemia of Malignancy
Take chest x-ray
Bloods show high Ca2+ and high phosphate
Malignancy causes unregulated breakdown of bone, increasing plasma Ca2+
ECG shows tented T wave and short QT interval
Most commonly in myeloma and non hodgkin lymphoma