Hypoparathyroidism Flashcards
Primary Hypoparathyroidism
Primary hypoparathyroidism decrease PTH secretion e.g. secondary to thyroid surgery* low calcium, high phosphate treated with alfacalcidol
*this may seem an oxymoron, but most medical textbooks classify hypoparathyroidism which is secondary to surgery as being ‘primary hypoparathyroidism’
Hypoparathyroidism - Sx
The main symptoms of hypoparathyroidism are secondary to hypocalcaemia:
tetany: muscle twitching, cramping and spasm
perioral paraesthesia
Trousseau’s sign: carpal spasm if the brachial artery occluded by inflating the blood pressure cuff and maintaining pressure above systolic
Chvostek’s sign: tapping over parotid causes facial muscles to twitch
if chronic: depression, cataracts
ECG: prolonged QT interval
Pseudohypoparathyroidism
Pseudohypoparathyroidism
target cells being insensitive to PTH
due to abnormality in a G protein
Typically inherited in autosomal dominant fashion
T1 pseudohypoparathyroidism = Complete receptor defect
T2 pseudohypoparathyroidism = Cell receptor is intact
associated with low IQ/cognitive impairment short stature shortened 4th and 5th metacarpals obesity round face
Bloods: low calcium, high phosphate, high PTH
Ix: diagnosis is made by measuring urinary cAMP and phosphate levels following an infusion of PTH. In hypoparathyroidism this will cause an increase in both cAMP and phosphate levels.
In pseudohypoparathyroidism type I neither cAMP nor phosphate levels are increased whilst in pseudohypoparathyroidism type II only cAMP rises, phosphate levels don’t change
Pseudopseudohypoparathyroidism
similar phenotype to pseudohypoparathyroidism but normal biochemistry
Calcium Target in Hypoparathyroidism - Example Question
An 18-year-old man comes to the endocrinology clinic for review. He has been transferred from the paediatric clinic with a diagnosis of congenital hypoparathyroidism and is treated with vitamin D and calcium supplementation. He has had one episode of symptomatic renal stones over the past 3 years and his creatinine is elevated at 125 micromol/l.
Which of the following is the most appropriate target with respect to serum calcium?
1.85 mmol/l > 2.10 mmol/l 2.25 mmol/l 2.60 mmol/l 2.85 mmol/l
This 18-year-old man is at risk of symptomatic hypocalcaemia because of congenital hypoparathyroidism, although elevating his calcium too much with vitamin D supplementation runs the risk of symptomatic renal stones. As such guidelines recommend aiming towards a calcium just below the lower end of the normal range and 2.10 is an appropriate target for serum calcium.
1.85 mmol/l is considered too low and puts the patient at risk of muscle weakness, paresthesias, tetany and cardiac arrhythmia. Maintenance of calcium either at the upper end of the normal range, (2.60 mmol/l), or 2.85 mmol/l (above the normal range), is associated with symptomatic renal stones and progressive deterioration in renal function.
The European Endocrine Society Guidelines support his calcium target: (page G2)
http://www.eje-online.org/content/173/2/G1.full.pdf
Congenital Hypoparathyroidism - Target Calcium
Guidelines recommend aiming towards a calcium just below the lower end of the normal range and 2.10 is an appropriate target for serum calcium.
1.85 mmol/l is considered too low and puts the patient at risk of muscle weakness, paresthesias, tetany and cardiac arrhythmia.
Maintenance of calcium either at the upper end of the normal range, (2.60 mmol/l), or 2.85 mmol/l (above the normal range), is associated with symptomatic renal stones and progressive deterioration in renal function.
Pseudohypoparathyroidism
A surgical Foundation Year 1 doctor (FY1) asks you to review a preoperative ECG for a 19-year-old patient who has been admitted under their team with suspected appendicitis. The only abnormality is a prolonged QT and you note the adjusted calcium to be 2.02 mmol/l.
The FY1 tells you that when they looked at the patients closed fists the outer two knuckles looked like dimples. She also tells you that the patient’s body mass index is 29 kg/m².
You ask her to order some blood tests which come back as follows:
Adjusted calcium 2.02 mmol/l
PTH 69 pmol/L (normal range = 0.8 - 8.5)
Phosphate 2.0 mmol/l
ALP 130 u/l
What is the most likely underlying cause for this patient’s hypocalcaemia?
Hypoparathyroidism > Pseudohypoparathyroidism type 1a Pseudohypoparathyroidism type 1b Pseudopseudohypoparathyroidism Secondary hyperparathyroidism
This patient has a high PTH, a low calcium, a high phosphate and a normal ALP. The patient is also obese and the dimples on the outer two knuckles are likely to represent shortening of the 4th and 5th metacarpals. This biochemistry in combination of these clinical features is characteristic of pseudohypoparathyroidism Type 1a (Albright’s Hereditary Osteodystrophy).
Pseudopseudohypoparathyroidism would have the same clinical features but would have normal biochemistry. Pseudohypoparathyroidism Type 1b would have the same biochemistry but lack the clinical features.
This patient has a high PTH, therefore this immediately excludes hypoparathyroidism. In secondary hyperparathyroidism the ALP would be elevated therefore this is incorrect.
