Week 12 - Diabetes insipidus, hyperparathyroidism, hypoparathyroidism

Question 1

what are the two reasons as to why diabetes insipidus occurs

Answer 1

A lack of antidiuretic hormone (cranial diabetes insipidus)

A lack of response to antidiuretic hormone (nephrogenic diabetes insipidus)

Question 2

where is antidiuretic hormone produced

Answer 2

in the hypothalamus and secreted by the posterior pituitary gland

it is also known as vasopressin

Question 3

what does ADH do

Answer 3

stimulates water reabsorption from the collecting ducts in the kidneys

Question 4

what happens in diabetes insipidus due to the kidneys being unable to reabsorb water and concentrate the urine

Answer 4

Polyuria (excessive amounts of urine)
Polydipsia (excessive thirst)

Question 5

what is primary polydipsia

Answer 5

Primary polydipsia is when the patient has a normally functioning ADH system but drinks excessive amounts of water, leading to excessive urine production (polyuria). This is not diabetes insipidus.

Question 6

what is nephrogenic diabetes

Answer 6

is when the collecting ducts of the kidneys do not respond to ADH. it can be idiopathic without a clear cause, or it can be caused by other things

Question 7

what are the other things that can cause nephrogenic diabetes insipidus

Answer 7

Medications, particularly lithium (used in bipolar affective disorder)
Genetic mutations in the ADH receptor gene (X-linked recessive inheritance)
Hypercalcaemia (high calcium)
Hypokalaemia (low potassium)
Kidney diseases (e.g., polycystic kidney disease)

Question 8

what is cranial diabetes insipidus

Answer 8

when the hypothalamus does not produce ADH for the pituitary gland to secrete. it can be idiopathic, without a clear cause or…

Question 9

what else can cranial diabetes insipidus be caused by

Answer 9

Brain tumours
Brain injury
Brain surgery
Brain infections (e.g., meningitis or encephalitis)
Genetic mutations in the ADH gene (autosomal dominant inheritance)
Wolfram syndrome (a genetic condition also causing optic atrophy, deafness and diabetes mellitus)

Question 10

what are the presenting features of diabetes insipidus

Answer 10

Polyuria (producing more than 3 litres of urine per day)
Polydipsia (excessive thirst)
Dehydration
Postural hypotension

Question 11

what do investigations into diabetes insipidus

Answer 11

Low urine osmolality (lots of water diluting the urine)

High/normal serum osmolality (water loss may be balanced by increased intake)

More than 3 litres on a 24-hour urine collection

Question 12

what is the test of choice for diagnosing diabetes insipidus

Answer 12

water deprivation test

Question 13

what is included in the water deprivation test

Answer 13

The patient avoids all fluids for up to 8 hours before the test (water deprivation). After water deprivation, urine osmolality is measured. If the urine osmolality is low, synthetic ADH (desmopressin) is given. Urine osmolality is measured over the 2-4 hours following desmopressin.

Question 14

what happens to the results of the water deprivation test in patients with primary polydipsia

Answer 14

In primary polydipsia, water deprivation will cause urine osmolality to be high. Desmopressin does not need to be given. A high urine osmolality after water deprivation rules out diabetes insipidus.

Question 15

what happens to the results of the water deprivation test in cranial diabetes insipidus

Answer 15

In cranial diabetes insipidus, the patient lacks ADH. The kidneys are still capable of responding to ADH. Initially, the urine osmolality remains low as it continues to be diluted by the excessive water lost in the urine. After desmopressin is given, the kidneys respond by reabsorbing water and concentrating the urine. The urine osmolality will be high

Question 16

what happens to the results of the water deprivation test in nephrogenic diabetes insipidus

Answer 16

In nephrogenic diabetes insipidus, the patient is unable to respond to ADH. The urine osmolality will be low both before and after the desmopressin is given.

Question 17

how is cranial diabetes insipidus treated

Answer 17

desmopressin can be used to replace the absent ADH hormone. the serum sodium needs to be monitored, as there is a risk of hyponatraemia with desmopressin

Question 18

what does management of nephrogenic diabetes insipidus include

Answer 18

Ensuring access to plenty of water
High-dose desmopressin
Thiazide diuretics
NSAIDs

Question 19

what does the parathyroid hormone act to do

Answer 19

raise the blood calcium level

Question 20

how does the PTH raise the blood calcium level

Answer 20

Increasing osteoclast activity in bones (reabsorbing calcium from bones)

Increasing calcium reabsorption in the kidneys (less calcium is lost in urine)

Increasing vitamin D activity, resulting in increased calcium absorption in the intestines

Question 21

what does vitamin D do to calcium absorption from the intestines

Answer 21

acts to increase calcium absorption

Question 22

what does PTH do to vitamin D

Answer 22

converts it into its active form.

therefore, vitamin D and parathyroid hormone act to raise blood calcium level

Question 23

what are the symptoms of hypercalaemia

Answer 23

Kidney stones
Painful bones
Abdominal groans (constipation, nausea and vomiting)
Psychiatric moans (fatigue, depression and psychosis)

Question 24

what is primary hypoerparathyroidism caused by

Answer 24

uncontrolled PTH production by a tumour of the parathyroid glands.

this leads to a raised blood calcium.

Question 25

what is secondary hyperparathyroidism

Answer 25

Secondary hyperparathyroidism is where insufficient vitamin D or chronic kidney disease reduces calcium absorption from the intestines, kidneys and bones. This result in low blood calcium (hypocalcaemia). The parathyroid glands react to the low serum calcium by excreting more parathyroid hormone. The serum calcium level will be low or normal, but the parathyroid hormone will be high. Treatment is to correct the underlying vitamin D deficiency or chronic kidney disease (e.g., renal transplant).

Question 26

what is tertiary hyperparathyroidism

Answer 26

Tertiary hyperparathyroidism happens when secondary hyperparathyroidism continues for an extended period, after which the underlying cause is treated. Hyperplasia (growth) of the parathyroid glands occurs as they adapt to producing a higher baseline level of parathyroid hormone. Then, when the underlying cause of the secondary hyperparathyroidism is treated, the baseline parathyroid hormone production remains inappropriately high. In the absence of the previous pathology, this high parathyroid hormone level leads to the inappropriately high absorption of calcium in the intestines, kidneys and bones, causing hypercalcaemia. Treatment is surgically removing part of the parathyroid tissue to return the parathyroid hormone to an appropriate level.

Question 27

in what cases is hyperparathyroidism most clinically signifiant in

Answer 27

chronic kidney disease