Parathyroid Disorders Flashcards
PTH secretion increases in response to low levels of which two minerals/vitamins?
What element is required for PTH production?
Stimuli - Low levels of calcium (+/- low levels of Vitamin D)
Required element - Magnesium
What is the mechanism of Ca induced PTH production
- Calcium binding to Ca-sensing receptors (g-protein coupled receptors), causing a negative feedback loop
- I.e. in the presence & binding of Ca, PTH production reduces
- Increased Ca ⇒ Decreased PTH (⇒ Decreased Ca)
- Decreased Ca ⇒ Increased PTH (⇒ Increased Ca)
Vitamin D is hydroxylated in the kidneys. Name a stimulating and an inhibitory factor
- Stimulating - PTH
- Inhibition - Phosphate
Vitamin D insufficiency can be due to problems with availability, absorption and metabolism (to active form).
Name 3 reasons for reduced Vitamin D availability and absorption
- Food intake e.g. elderly, immigrants
- Limited sunlight exposure (MAIN)
- Anticonvulsants
Vitamin D insufficiency can be due to problems with availability, absorption and metabolism (to active form).
Name some reasons for poor Vitamin D metabolism
- Renal failure or nephrectomy
- Hyperphophataemia
- Hypoparathyrodisim
- Rickets
- Oncogenic osteomalacia
What is hyperparathyroidism
The overactivity of the parathyroid glands resulting in high PTH
State the main functions of PTH
Calcium release (activated osteoclasts), calcium absorption (increased Vitamin D), calcium conservation (calcium reabsorption), calcium availability (phosphate excretion)
- Calcium release: PTH (activates osteoclasts & so) signals bones to release calcium into the bloodstream.
- Calcium absorption: PTH stimulates the kidneys to convert weaker forms of vitamin D into the form that best absorbs calcium from the intestines.
- Calcium conservation: PTH helps the kidneys conserve calcium by preventing it from being released in urine.
- Calcium availability: PTH increases urinary phosphate excretion, meaning there is less phosphate to bind to calcium
Compare primary vs secondary vs tertiary hyperPTH with regards to aetiology, calcium levels, phosphate levels, management
Primary
- Aetiology - Parathyroid adenoma/carcinoma/hyperplasia
- Ca levels - High
- Phosphate levels - Low
- Management - Tumour surgical removal
Secondary
- Aetiology - CKD/ Vitamin D deficiency
- Ca levels - low
- Phosphate levels - (vit D) low, (CKD) high
- Management - Aetiology based
Tertiary
- Aetiology - Prolonged secondary hyperPTH => autonomous secretion
- Ca levels - high
- Management - partial gland surgical removal
A complication of hyperparathyroidism is fibrosa cystica. Describe the three features of this.
- Osteoporosis
- Brown tumours (lytic lesion haemorrhage & inflammatory response to osteoporotic fractures)
- Osteitis
If surgery is not possible for someone with hyperPT, what drug can be used? What is its MOA
Cinacalcet - a calcium mimetic, reduces PTH
Subtotal and total parathyroidectomy is often used to treat primaryPT and tertiaryPT. Name two complications of this.
- Hypocalcaemia
- Recurrent laryngeal nerve palsy
What is Familial Hypocalciuric hypercalcaemia (FHH)
- Autosomal dominant, deactivating mutation in the calcium sensing receptor
- Usually asymptomatic
Hypercalcaemia aetiology
- Excessive PTH secretion
- Primary hyperPT
- Tertiary hyperPT
- Malignancy
- Metastatic bone destruction
- PTHrp secreting tumours
- Osteoclastic activating factor secreting tumours
- Other
- DRUG - Thiazides
- GRANULOMA - Sarcoidosis, TB,
- GENETIC - MEN 1& 2, FHH
- HIGH BONE TURNOVER RATE - thyrotoxic, paget’s
(Chronic) Hypercalcaemia symptoms
- Bones - osteopenia, fractures
- Kidney Stones
- Abdominal groans - pain, nausea, pancreatitis, duodenal ulcers
- Psychic moans - depression
- (Other) - proximal myopathy, hypertension
(Acute) Hypercalcaemia symptoms
- Renal - Thirst, polyuria, dehydration
- Psych - Confusion
