Parathyroid Flashcards
(41 cards)
How many parathyroid glands are there normally?
4
Where are the parathyroid glands located?
Posterior to the thyroid
Which cells secrete PTH and in response to what?
Chief cells - in response to a decrease in Ca2+ serum levels
What detects a decrease in serum calcium?
Specific G-protein coupled, calcium-sensing receptors on the plasma membrane of the parathyroid glands
What is the function of calcium in the body?
- Muscle contraction and regulation, especially in the heart
- Building strong bones and teeth
- Nerve impulse transmission
- Oocyte activation
- Fluid balance in cells
State the 5 actions of PTH
- Increases calcium absorption from the gut via activation of vitamin D
- Increases bone resorption
- Increases bone turnover and osteoclast activity
- Releases Ca2+ from the bone reservoir
- Net loss of bone
- Activation of 1,25-dihydroxyvitamin D (calcitriol) in the kidney
- Increasing renal tubular reabsorption of Ca2+
- Increasing excretion of phosphate
What is a reason for apparent hypocalcaemia?
Hypoalbinaemia - it can cause changes in calcium measurement
Who is most commonly affected by hypocalcaemia?
Hospitalised patients (of any age/sex) - it correlates with the severity of the illness
What is the equation to find the corrected calcium level?
Corrected calcium = total serum calcium + 0.02 x (40 - serum albumin)
Give 7 consequences of hypocalcaemia
- Paraesthesia (pins and needles) particularly around the mouth, hands and feet
- Tetany (muscle spasm/cramps) in the hands, feet, larynx
- Can cause premature labour due to uterus spasm
- Seizures and coma
- ECG abnormalities
- Basal ganglia calcification (in chronic)
- Cataracts (in chronic)
What ECG abnormalities will be seen in hypocalcaemia?
A long QT interval (leads to dysrhythmias)
What is Chvostek’s sign?
- Tapping over the facial nerve in the region of the parotid gland causes twitching of the facial muscles on the same side (ipsilateral)
- A classical sign of hypoparathyroidism
What is Trousseau’s sign?
- Carpopedal spasm induced by inflation of blood pressure cuff to a level above systolic blood pressure
- A classical sign of hypoparathyroidism
What are the causes of hypocalcaemia?
- Chronic kidney disease (most common cause of hypocalcaemia)
- Vitamin D deficiency
- Primary hypoparathyroidism
- Secondary hypoparathyroidism
- Pseudohypoparathyroidism
- Pseudopseudohypoparathyroidism
- Drugs
- Acute pancreatitis (with normal or reduced phosphate)
- Osteomalacia (with normal or reduced phosphate)
What can cause vitamin D deficiency?
- Reduced UV exposure
- Malabsorption
- Anti-epileptic drugs
- Vitamin D resistance (rare)
What is hypoparathyroidism?
Low PTH due to parathyroid gland failure
What are the causes of primary hypoparathyroidism?
- Autoimmune DiGeorge syndrome
2. Idiopathic hypoparathyroidism
What are the causes of secondary hypoparathyroidism?
- After parathyroidectomy or thyroidectomy surgery
- It is the most common hypoparathyroidism
- Radiation
- Hypomagnesaemia - Mg is required for PTH secretion
What is pseudohypoparathyroidism and what are features of it?
• Failure of target cell response to PTH
Give 5 features of pseudohypoparathyroidism
- Short stature
- Short metacarpals (especially 4th and 5th)
- Subcutaneous calcification
- Sometimes intellectual impairment
- Low Ca2+ and high PTH
How does pseudopseudohypoparathyroidism differ to pseudohypoparathyroidism?
Pseudopseudo doesn’t have any abnormalities of Ca2+ metabolism but they have the same phenotypic defects
Give 4 differential diagnoses for tetany
- Hypocalcaemia
- Alkalosis
- K+ and Mg2+ deficiency
- Hyperventilation
How would you diagnose hypocalcaemia?
• Clinical history and features
• Low serum calcium after correction for albumin abnormalities
• Serum urine and creatinine as well as eGFR to test for renal disease
• PTH levels in serum
- Absent or low in hypoparathyroidism
- High in other causes of hypocalcaemia
• Parathyroid antibodies - present in idiopathic hypoparathyroidism
• 25-hydroxyvitamin D serum level - low in vitamin D deficiency
• Mg2+ level - severe hypomagnesaemia result in functional hypoparathyroidism
How would you treat hypocalcaemia?
• Acute e.g. with tetany
- Admit to hospital if severe with symptoms
- Give IV calcium gluconate over 30 mins with ECG monitoring
• Vitamin D deficiency
- Given oral colcalciferol (vitamin D3) or can be given oral adcal (calcium + vitamin D3)
- This treatment is ineffective for those with hypoparathyroidism as PTH is needed for conversion of vitamin D3 to 1,25 dihydroxyvitamin D
• Hypoparathyroidism
- Given calcium supplements + calcitriol (active vitamin D)
