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Endocrinology > Endo - Diabetes Insipidus, SIADH > Flashcards

Endo - Diabetes Insipidus, SIADH Flashcards

1
Q

Diabetes Insipidus - what is it?

A

Lack of ADH
or
Lack of response to ADH

This prevents kidneys from being able to concentrate the urine, leading to classic symptoms of polyuria and polydipsia

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2
Q

Diabetes Insipidus - how can it be classified?

A

Cranial

Nephrogenic

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3
Q

Diabetes Insipidus - what is nephrogenic diabetes insipidus?

A

Nephrogenic Diabetes Insipidus (NDI), is when the collecting ducts of kidneys do not respond to ADH

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4
Q

Diabetes Insipidus - what are the causes of NDI?

A
  1. Drugs e.g. Lithium
  2. Electrolyte abnormalities - HYPOkalaemia and HYPERcalcaemia
  3. Mutations in genetics
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5
Q

Diabetes Insipidus - what is cranial diabetes insipidus, and what are the causes?

A

Cranial diabetes insipidus (CDI) is reduced secretion of ADH

Causes:

  1. Idiopathic (most common)
  2. Brain tumours
  3. Head injury
  4. Brain infections - meningitis, encephalitis
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6
Q

Diabetes Insipidus - presentation

A

Polyuria

Polydipsia

Nocturia

Hypernatraemia

Dehydration

Postural hypotension

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7
Q

Diabetes Insipidus - investigations and their results

A

Low urine osmolality (diluted urine)

High serum osmolality (concentrated)

Water deprivation test - used to diagnose DI

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8
Q

Diabetes Insipidus - what does the water deprivation test entail?

A
  1. Patient has no fluids for 8 hours
  2. Urine osmolality then measured
  3. Synthetic ADH administered
  4. 8 hours later urine osmolality measured again
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9
Q

Diabetes Insipidus - water deprivation results and what they mean?

A

Cranial DI - patient lacks ADH, kidneys still capable of responding to ADH, so once synthetic ADH given, there will be a response with high urine osmolality

NDI - unable to respond to ADH, so even after giving synthetic ADH there is no response, urine osmolality is still low

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10
Q

Diabetes Insipidus - management

A

Treat underlying cause

Desmopressin (synthetic ADH) can be used in:

  1. CDI to replace lack of ADH being secreted
  2. NDI, give thiazides, low salt/protein diet
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11
Q

SIADH - what is it?

A

Syndrome of Inappropriate Anti-diuretic Hormone (SIADH), is a condition where there is inappropriately large amounts of ADH

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12
Q

SIADH - where is ADH produced and secreted from, and what is its function?

A

Produced - hypothalamus

Secreted - posterior pituitary gland

ADH stimulates and increases water reabsorption from collecting ducts in kidneys, INDEPENDENT of sodium

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13
Q

SIADH - causes?

A

PP secreting too much ADH, or ADH produced from somewhere else like in SCLC

Various causes which can be split into categories,

Drugs:

  1. SSRIs, Tricyclics
  2. Carbamazepine

Malignancy:

  1. SCLC
  2. Neuroblastoma

Infective:

  1. Pneumonia
  2. TB
  3. HIV

Neurological:

  1. Stroke
  2. Subarachnoid haemorrhage
  3. Subdural haemorrhage
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14
Q

SIADH - what are the symptoms?

A

Non-specific

  1. Headache
  2. Fatigue
  3. Muscle cramps
  4. Lethargy
  5. Anorexia

Large proportion of cases asymptomatic, features only develop with severe HYPONATRAEMIA

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15
Q

SIADH - why does hyponatraemia occur?

A
  1. SIADH results in kidneys retaining more water
  2. Increase in total body water (TBW)
  3. Leads to dilutional hyponatraemia
  4. Increase in TBW, causes increase in extracellular fluid volume, which results in increased urinary sodium excretion
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16
Q

SIADH - what are the signs?

A

Seizures

Reduced GCS

Hyporeflexia

Ataxia

17
Q

SIADH - how do you diagnose, and what are the results?

A

SIADH more a diagnosis of exclusion, no single test that definitively diagnoses SIADH

Diagnosis based on clinical chemistry and patients history

Blood tests will show:
Serum Sodium will show hyponatraemia
Serum osmolality - LOW

Urinary tests will show:
Urinary osmolality - HIGH
Urine Sodium - HIGH

18
Q

SIADH - management

A

Establish and treat underlying cause, and correct any hyponatraemia SLOWLY, otherwise will lead to osmotic demyelination syndrome

  1. Fluid restriction, restrict fluid intake to 500ml-1L, may be enough to correct hyponatraemia
  2. TOLVAPTAN, ADH receptor blockers, powerful, cause rapid Na+ increase, so require 6hr monitoring
19
Q

SIADH - what is osmotic demyelination syndrome and what are the symptoms?

A

Complication of long term hyponatraemia (<120mmols/L) being treated too quickly (no more than >10mmol/L over 24 hours)

Symptoms usually occur after 2 days, usually irreversible: dysarthria, dysphagia, paraparesis or quadriparesis, seizures, confusion, and coma,
patients are awake but are unable to move or verbally communicate, also called ‘Locked-in syndrome’

Prevention essential, as treatment only supportive once CPM occurs

Endocrinology (9 decks)

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