Pituitary Disease - SIADH

Question 1

Function of ADH.

Answer 1

1. Produced in Hypothalamus.
2. Secreted by Posterior Pituitary Gland.
3. Stimulates water resorption in the collecting ducts in the kidneys.

Question 2

What is SIADH?

Answer 2

Syndrome of Inappropriate ADH Secretion.

Question 3

Pathophysiology of SIADH.

Answer 3

1. Excessive ADH - Excessive Water Resorption in Collecting Ducts.
2. Hyponatraemia (Dilution).
3. Euvolaemic Hyponatraemia.
4. High Urine Osmolality and High Urine Sodium.

Question 4

Clinical Features of SIADH (5).

Answer 4

1. Headache.
2. Fatigue.
3. Muscle Aches/Cramps.
4. Confusion.
5. Severe Hyponatraemia - Seizures, Reduced Consciousness.

Question 5

Aetiology of SIADH (2) - MAIN.

Answer 5

1. Posterior Pituitary Overproduction.

2. Ectopic Production.

Question 6

Aetiology of SIADH (6).

Answer 6

1. Post-Operative.
2. Infection e.g. Atypical Pneumonia, Lung Abscess.
3. Head Injury.
4. Medications.
5. Malignancy - SCLC.
6. Meningitis.

Question 7

Investigations of SIADH.

Answer 7

1. Diagnosis of Exclusion.
2. Euvolaemic Hyponatraemia.
3. High Urine Osmolality and High Urine Sodium.

Question 8

Differentials of Hyponatraemia to Exclude (5).

Answer 8

1. Adrenal Insufficiency - Short Synacthen Test.
2. History of Diuretic Use.
3. Diarrhoea, Vomiting, Burns, Fistulae, Excessive Sweating.
4. Excessive Water Intake.
5. CKD/AKI.

Question 9

Management.

Answer 9

1. Identify Underlying Cause.
2. Fluid Restriction (500ml-1L).
3. Tolvaptan.
4. Demeclocycline (not anymore).

Question 10

What is Tolvaptan?

Answer 10

ADH Receptor Blocker - rapid increase in Sodium, but requires close monitoring of Sodium levels every 6 hours.

Question 11

What is Central Pontine Myelinolysis?

Answer 11

Osmotic Demyelination Syndrome - a complication of long-term severe hyponatraemia being treated too quickly.

Question 12

Pathophysiology of Central Pontine Myelinolysis (4).

Answer 12

1. Serum Sodium falls.
2. Water moves by osmosis across blood-brain barrier.
3. Brain tries to adapt by reducing solutes in brain cells
4. If Sodium levels rapidly rise, water will rapidly shift out of the brain cells.

Question 13

Phases of Central Pontine Myelinolysis (2).

Answer 13

1. 1st - Electrolyte Imbalance - Encephalopathy and Confusion and Headache.
2. 2nd - Demyelination of Neurones in Pons - Spastic Quadriparesis, Pseudobulbar Palsy, Cognitive Behavioural Changes.

Question 14

Prognosis of Central Pontine Myelinolysis.

Answer 14

Supportive.