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Year Two - Endocrine System > Diabetes Insipidus > Flashcards

Diabetes Insipidus Flashcards

1
Q

What is diabetes insipidus?

A

A condition in which there is a lack of the antidiuretic hormone (ADH) or a lack of response to ADH

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2
Q

What is primary polydipsia?

A

A condition in which the patient has a normally functioning ADH system but is drinking excessive amounts of water leading to polyuria

These patients don’t have diabetes insipidus

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3
Q

What is another common cause of polyuria and polydipsia - which is not pathological?

A

Binge drinking alcohol

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4
Q

How does alcohol result in polyuria and polydypsia?

A

It inhibits ADH secretion

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5
Q

What are the two classifications of diabetes insipidus?

A

Nephrongenic

Cranial

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6
Q

What is nephrogenic diabetes insipidus?

A

It occurs when the collecting ducts of the kidneys don’t respond to ADH

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7
Q

What are the four causes of nephrogenic diabetes insipidus?

A

Genetic Disorder

Kidney Disease

Drugs

Electrolyte Disturbance

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8
Q

Which genetic mutation is associated with nephrogenic diabetes insipidus? What is the function of this gene? What is the inheritance of this genetic mutation?

A

AVPR2 gene

It codes for the ADH receptor

X-linked, recessive condition

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9
Q

What three kidney disease are associated with nephrogenic diabetes insipidus?

A

Renal calculi

Pyelonephritis

Sickle cell anaemia

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10
Q

What two drugs are associated with nephrogenic diabetes insipidus?

A

Lithium

Demeclocycline

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11
Q

What two electrolyte disturbances are associated with nephrogenic diabetes insipidus?

A

Hypokalaemia

Hypercalcaemia

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12
Q

What is another term for cranial diabetes insipidus?

A

Central diabetes insipidus

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13
Q

What is cranial diabetes insipidus?

A

It occurs when the hypothalamus doesn’t produce ADH for the pituitary gland to secrete

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14
Q

What are the five causes of cranial diabetes insipidus?

A

Genetic Disorders

Brain Tumours

Brain Infections

Brain Surgery

Head Injury

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15
Q

What two genetic disorders are associated with cranial diabetes insipidus?

A

Haemochromatosis

Histiocytosis X

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16
Q

What two brain tumours are associated with diabetes insipidus?

A

Pituitary adenoma

Craniopharyngioma

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17
Q

Which three brain infections are associated with diabetes insipidus?

A

Meningitis

Encephalitis

Tuberculosis

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18
Q

What are the three clinical features of diabetes insipidus?

A

Polyuria

Polydipsia

Dehydration

19
Q

What is polyuria?

A

It is defined as the production of excessive pale, urine production

20
Q

What 24-hour urine volume indicates diabetes insipidus?

A

50mg/kg

21
Q

What is polydipsia?

A

It is defined as excessive thirst

22
Q

What are the five investigations used to diagnose diabetes insipidus?

A

Plasma osmolality

Urine osmolality

Water deprivation test

MRI scan

Copeptin blood test

23
Q

How do we measure plasma and urine osmolality?

A

We obtain a blood sample and a urine sample from the patient

24
Q

What plasma osmolality level indicates diabetes insipidus?

A

High

Specifically, over 295mOsm/kg

25
Q

What urine osmolality level indicates diabetes insipidus?

A

Low

Specifically, less than 300mOsm/kg water

26
Q

What is another name for the water deprivation test?

A

Desmopressin stimulation test

27
Q

What is the gold standard investigation used to diagnose diabetes insipidus?

A

Water deprivation test

28
Q

How do we conduct the water deprivation test?

A

Initially, the patient should avoid taking in any fluids for eight hours. This is referred to as fluid deprivation

Then, urine osmolality is measured and synthetic ADH is administered

After eight hours, urine osmolality is measured again

29
Q

What initial urine osmolality in the water deprivation test immediately eliminates a diagnosis of diabetes insipidus?

A

Over 600mOsm/kg water

30
Q

What water deprivation test results indicate cranial diabetes insipidus? Explain this

A

In cranial diabetes insipidus, the patient lacks ADH. The kidneys are still capable or responding to ADH

Therefore, initially the plasma osmolality remains low as it continues to be diluted by excessive water secretion in the kidneys

Then when synthetic ADH is given, the kidneys respond by reabsorbing water and concentrating the urine, so the urine osmolality will be high

31
Q

What water deprivation test results indicate nephrogenic diabetes insipidus? Explain this

A

In nephrogenic diabetes insipidus, the patient is unable to respond to ADH

They are diluting their urine with the excessive water secretion from the kidneys

Therefore, the urine osmolality will be low initially and remain low even after the synthetic ADH is given

32
Q

What water deprivation test results indicate primary polydipsia? Explain this

A

In primary polydipsia, the eight hours of water deprivation will cause the urine osmolality to be high even before the synthetic ADH is given

33
Q

What sodium levels during the water deprivation test further indicate a diagnosis of diabetes insipidus?

A

High

Specifically, levels over 146

34
Q

How is an MRI scan used to diagnose diabetes insipidus?

A

It can detect any abnormalities within the brain - which can identify the underlying cause of cranial diabetes insipidus

35
Q

What is copeptin?

A

A reliable surrogate marker of ADH

Therefore, the levels of copeptin reflect the levels of ADH

36
Q

When do we conduct the copeptin blood test?

A

This investigation is conducted in patients with a urine osmolality less then 100

37
Q

What copeptin blood test level indicates a diagnosis of nephrogenic diabetes insipidus?

A

A random copeptin level over 21.4

38
Q

What copeptin blood test level indicates a diagnosis of cranial diabetes insipidus?

A

A random copeptin level less than 21.4

A stimulated copeptin level of less than 4.9

39
Q

What copeptin blood test level indicates a diagnosis of primary polydipsia?

A

A random copeptin level less than 21.4

A stimulated copeptin level greater than 4.9

40
Q

How do we treat cranial diabetes insipidus?

A

We prescribe patients synthetic ADH, which is known as desmopressin

If the patient’s condition is caused by an abnormality within the pituitary gland or hypothalamus, we can try and treat the underlying cause initially

41
Q

What is another term for synthetic desmopressin?

A

Vasopressin V2 receptor agonist

42
Q

What are the four ways in which we treat nephrogenic diabetes insipidus?

A

High Dose Desmopressin

Thiazide Diuretics

Prostaglandin Synthase Inhibitors

Correct Electrolyte Imbalance

43
Q

Name two thiazide diuretics used to treat nephropgenic diabetes insipidus

A

Hydrochlorothiazide

Bendroflumethiazide

44
Q

What are the three electrolyte imbalances associated with diabetes insipidus?

A

High Na+

Low K+

High Ca+

Year Two - Endocrine System (17 decks)

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