Hypocalcemia Flashcards
Identify the condition described
Cardiac defects - Truncus arteriosus, Tetralogy of Fallot
Abnormal facies
Thymic hypoplasia–> T cell deficiency–> recurrent viral/ fungal infections
Cleft palate
Hypocalcemia secondary to parathyroid aplasia
22q11 microdeletion
DiGeorge Syndrome
Embryologic defect in DiGeorge syndrome that leads to hypocalcemia
failure to develop 3rd and 4th branchial (pharyngeal) pouches–> absent thymus and parathyroid glands
Components of Autoimmune polyendocrine failure syndrome-1(APS-1)
chronic mucocutaneous candidiasis+ primary adrenal insufficiency+ hypoparathyroidism
Cause for Autoimmune polyendocrine failure syndrome 1(APS-1).
mutations in the autoimmune regulator (AIRE) gene
most common cause of hypocalcemia in a hospital setting
Hypomagnesemia
Underlying mechanism of autosomal-dominant hypoparathyroidism
gain-of-function mutations in the calcium-sensing receptor (CASR) gene
Why are alkaline phosphatase levels elevated in Vitamin D deficiency?
Vitamin D deficiency –> impaired intestinal absorption of calcium—>PTH elevated–> increased bone turnover–> ALP elevated
How does hypophosphatemia occur in Vitamin D deficiency?
Vitamin D deficiency –> impaired intestinal absorption of calcium—>PTH elevated–> promotes renal phosphate excretion–>hypophosphatemia
How does Vitamin D deficiency occur in chronic renal failure?
CRF–>impaired kidney function–>hampers the final conversion of 25-hydroxychalecalciferol to active 1,25-dihydroxycholecalciferol via 1-alpha hydroxylase
How does hypocalcemia occur in chronic renal failure?
- Failing kidneys—>poor calcium reabsorption
- deficiency of active vitamin D –> decreased intestinal absorption of calcium
Mechanism of renal osteodystrophy in chronic renal failure
Hyperphosphatemia & hypocalcemia –>upregulation of PTH–> increases bony turnover to raise serum calcium and promotes renal excretion of phosphate. Unregulated, this process results in renal osteodystrophy,
alternating dense-lucent-dense appearance in untreated chronic hyperparathyroidism
Rugger jersey spine
1.
Two radiologic features of long standing hyperparathyroidism
1.Rugger jersey spine
2.Pepper pot skull
What’s the cause of this appearnce?
Salt and pepper signorpepper pot skullrefers to multiple tiny well-defined lucencies in the calvaria caused by resorption of trabecular bone inhyperparathyroidism
Morphologic hallmark of osteomalacia on bone biopsy
Thickening of osteoid seams
Mechanism of Vitamin D–dependent rickets type I
mutations in the gene encoding 25(OH)D-1α-hydroxylase
Mechanism of Vitamin D–dependent rickets type II
mutations in the gene encoding the** vitamin D receptor**–>end-organ resistance to the active metabolite 1,25(OH)2D
Reason why plasma levels of 1,25(OH)2D are elevated in Vitamin D–dependent rickets type II
- of increased production due to stimulation of 1α-hydroxylase activity as a consequence of secondary hyperparathyroidism
- impaired inactivation since induction of the 24-hydroxylase by 1,25(OH)2D requires an intact vitamin D receptor
Underlying basis of pseudohypoparathyroidism
loss-of-function mutations in GNAS1–> inactivation of adenylate cyclase when PTH binds to its receptor creating–> end -organ resistance (kidney and bone) to PTH.
Phenotype of Albright hereditaty osteodystrophy
short stature, obesity, round facies, Mental retardation, basal ganglia calcification, short fourth and fifth metacarpals
Pseudopseudohypoparathyroidism
paternally transmitted mutations (imprinted GNAS gene) but without end-organ resistance to PTH due to normal maternal allele maintaining renal responsiveness to PTH.
What is a positive Chvostek sign?
Twitching of the ipsilateral facial muscles on tapping on the facial nerve anterior to the ear
What is a positive Trousseau sign?
inflating the sphygmomanometer with the cuff around the arm 20mmHg above the systolic blood pressure for 3 min–>painful carpal muscle contractions and spasms
Why do paresthesias develop in hypocalcemia?
neuromuscular irritability
What is tetany?
spontaneous tonic muscular contractions, manifested by painful carpal spasms and laryngeal stridor, in individuals with hypocalcemia
