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Endocrine > Parathyroid > Flashcards

Parathyroid Flashcards

1
Q

How many parathyroid glands are there normally?

A

4

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2
Q

Where are the parathyroid glands located?

A

Posterior to the thyroid

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3
Q

Which cells secrete PTH and in response to what?

A

Chief cells - in response to a decrease in Ca2+ serum levels

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4
Q

What detects a decrease in serum calcium?

A

Specific G-protein coupled, calcium-sensing receptors on the plasma membrane of the parathyroid glands

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5
Q

What is the function of calcium in the body?

A
  • Muscle contraction and regulation, especially in the heart
  • Building strong bones and teeth
  • Nerve impulse transmission
  • Oocyte activation
  • Fluid balance in cells
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6
Q

State the 5 actions of PTH

A
  1. Increases calcium absorption from the gut via activation of vitamin D
  2. Increases bone resorption
    • Increases bone turnover and osteoclast activity
    • Releases Ca2+ from the bone reservoir
    • Net loss of bone
  3. Activation of 1,25-dihydroxyvitamin D (calcitriol) in the kidney
  4. Increasing renal tubular reabsorption of Ca2+
  5. Increasing excretion of phosphate
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7
Q

What is a reason for apparent hypocalcaemia?

A

Hypoalbinaemia - it can cause changes in calcium measurement

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8
Q

Who is most commonly affected by hypocalcaemia?

A

Hospitalised patients (of any age/sex) - it correlates with the severity of the illness

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9
Q

What is the equation to find the corrected calcium level?

A

Corrected calcium = total serum calcium + 0.02 x (40 - serum albumin)

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10
Q

Give 7 consequences of hypocalcaemia

A
  1. Paraesthesia (pins and needles) particularly around the mouth, hands and feet
  2. Tetany (muscle spasm/cramps) in the hands, feet, larynx
  3. Can cause premature labour due to uterus spasm
  4. Seizures and coma
  5. ECG abnormalities
  6. Basal ganglia calcification (in chronic)
  7. Cataracts (in chronic)
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11
Q

What ECG abnormalities will be seen in hypocalcaemia?

A

A long QT interval (leads to dysrhythmias)

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12
Q

What is Chvostek’s sign?

A
  • 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
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13
Q

What is Trousseau’s sign?

A
  • Carpopedal spasm induced by inflation of blood pressure cuff to a level above systolic blood pressure
  • A classical sign of hypoparathyroidism
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14
Q

What are the causes of hypocalcaemia?

A
  1. Chronic kidney disease (most common cause of hypocalcaemia)
  2. Vitamin D deficiency
  3. Primary hypoparathyroidism
  4. Secondary hypoparathyroidism
  5. Pseudohypoparathyroidism
  6. Pseudopseudohypoparathyroidism
  7. Drugs
  8. Acute pancreatitis (with normal or reduced phosphate)
  9. Osteomalacia (with normal or reduced phosphate)
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15
Q

What can cause vitamin D deficiency?

A
  • Reduced UV exposure
  • Malabsorption
  • Anti-epileptic drugs
  • Vitamin D resistance (rare)
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16
Q

What is hypoparathyroidism?

A

Low PTH due to parathyroid gland failure

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17
Q

What are the causes of primary hypoparathyroidism?

A
  1. Autoimmune DiGeorge syndrome

2. Idiopathic hypoparathyroidism

18
Q

What are the causes of secondary hypoparathyroidism?

A
  1. After parathyroidectomy or thyroidectomy surgery
    • It is the most common hypoparathyroidism
  2. Radiation
  3. Hypomagnesaemia - Mg is required for PTH secretion
19
Q

What is pseudohypoparathyroidism and what are features of it?

A

• Failure of target cell response to PTH

20
Q

Give 5 features of pseudohypoparathyroidism

A
  1. Short stature
  2. Short metacarpals (especially 4th and 5th)
  3. Subcutaneous calcification
  4. Sometimes intellectual impairment
  5. Low Ca2+ and high PTH
21
Q

How does pseudopseudohypoparathyroidism differ to pseudohypoparathyroidism?

A

Pseudopseudo doesn’t have any abnormalities of Ca2+ metabolism but they have the same phenotypic defects

22
Q

Give 4 differential diagnoses for tetany

A
  1. Hypocalcaemia
  2. Alkalosis
  3. K+ and Mg2+ deficiency
  4. Hyperventilation
23
Q

How would you diagnose hypocalcaemia?

A

• 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

24
Q

How would you treat hypocalcaemia?

A

• 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)

25
Q

What is clinically more common: hypo or hypercalcaemia?

A

Hypercalcaemia

26
Q

What are the most common causes for hypercalcaemia?

A

Primary hyperparathyroidism and malignancies

27
Q

What are 3 reasons for apparent hypercalcaemia?

A
  1. Serum albumin is abnormal/hasn’t been corrected for
  2. Tourniquet on for too long (cell lysis releases Ca2+ )
  3. Blood sample is old and has haemolysed (cell lysis releases Ca2+ )
28
Q

Give some clinical presentations for hypercalcaemia

A
  • Asymptomatic if mild
  • Abdominal pains
  • Malaise
  • Nausea
  • Constipation
  • Polydipsia (thirst)
  • Calcium deposition in the renal tubules causing polyuria and nocturia
  • Dehydration, confusion, risk of cardiac arrest
  • Depression, anxiety, cognitive dysfunction, insomnia and coma
  • ECG abnormalities
29
Q

What ECG abnormalities will be seen in hypercalcaemia?

A

A short QT interval (leading to fatal dysrhythmia)

30
Q

Define hyperparathyroidism

A

Excessive PTH secretion

31
Q

What are the causes of hypercalcaemia?

A
  1. Primary hyperparathyroidism (most common cause)
  2. Secondary hyperparathyroidism
  3. Tertiary hyperparathyroidism
  4. Malignant hyperparathyroidism
  5. Excessive Ca2+ intake
  6. Drugs
  7. Long term immobility
32
Q

What are the causes of primary hyperparathyroidism?

A
  1. 80% due to adenoma on a parathyroid gland
  2. 20% due to hyperplasia of the parathyroid glands
  3. <0.5% due to parathyroid carcinoma
33
Q

What would you seen in the lab results for primary hyperparathyroidism?

A
  • PTH - high
  • Ca2+ - high
  • Phosphate - low (usually)
  • Alkaline phosphatase -high (usually)
34
Q

What is the cause of secondary hyperparathyroidism?

A

Compensatory hypertrophy of the parathyroid glands due to hypocalcaemia e.g. chronic kidney disease, vit D deficiency

35
Q

What would you seen in the lab results for secondary hyperparathyroidism?

A
  • PTH - high
  • Ca2+ - low
  • Phosphate - high (due to renal disease)
  • Alkaline phosphatase -high
36
Q

What is the cause of tertiary hyperparathyroidism?

A

After many years of secondary hyperparathyroidism the glands act autonomously and are not regulated by feedback control

37
Q

What would you seen in the lab results for tertiary hyperparathyroidism?

A
  • PTH - high
  • Ca2+ - high
  • Phosphate - high
  • Alkaline phosphatase -high
38
Q

What malignancies may cause hypercalcaemia?

A
  • Bone metastases
  • Myeloma
  • PTH related protein (PTHrP)
  • Lymphoma
  • Granular diseases e.g. TB, Sarcoidosis
39
Q

Give examples of drugs that may cause hypercalcaemia

A
  • Thiazide diuretics
  • Vitamin D analogies
  • Lithium administration
40
Q

What are some ways you would diagnose hypercalaemia?

A
  • Raised alkaline phosphatase
  • Lab result blood tests
  • A low PTH excludes hyperparathyroidism
  • Renal function measure
  • 24hr urinary calcium
  • Measure TSH to exclude hyperthyroidism
  • X-ray - calcium deposits, ‘pepper-pot skull’, subperiosteal phalange erosions
  • Parathyroid ultrasound - insensitive for small tumours
  • Radioisotope scanning - sensitive for detecting adenomas
  • High resolution CT or MRI
  • DXA bone density scan
41
Q

How would you treat hypercalcaemia?

A

• Acute severe hypercalcaemia is a medical emergency
- Rehydrate with IV 0.9% saline fluids
- Give bisphosphonates after rehydration e.g. IV PAMIDRONATE
- Measure serum U&E’s daily and serum Ca2+ 48hrs after initial treatment
- Can give glucocorticoid steroids e.g. ORAL PREDNISOLONE in myeloma, sarcoidosis and vitamin D excess
• Primary hyperparathyroidism:
- Parathyroid adenoma - surgical removal
- Parathyroid hyperplasia - all 4 glands are surgically removed
- Can give a calcimimetic that increases the sensitivity of parathyroid cells to Ca2+ thereby causing less PTH secretion e.g. ORAL CINACALCET - used when surgery is contraindicated
• Avoid THIAZIDE DIURETICS and high Ca2+ and vitamin D intake
• Exercise encouraged
• Treat the underlying causes
• Chemotherapy for malignancy

Endocrine (7 decks)

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