SIADH

Question 1

What are the causes of SIADH?

Answer 1

• Hypocortisolism (due to negative feedback -> 2’ SIADH)
• Hypothyroidism (2’ SIADH)
• Drugs (e.g., chlorpropamide, carbamazepine, cyclophosphamide, SSRIs)
• Ectopic ADH production: most commonly SCLC (Small Cell Lung Ca)

Question 2

What are the investigations to be conducted for SIADH?

Answer 2

1) TRO Hypocortisolism & Hypothyroidism
- Hypothyroidism: do TFT & TSH
- Hypocortisolism: do 8am cortisol (or equivalents)

2) Reduced Plasma Osmolality (normal = 285-295 mOsm/kg)
3) Inappropriately concentrated urine (Elevated Urine Osmolality)
4) Euvolemic Status
5) Elevated Urine Na (Institution based: TTSH > 20, KTPH >40)

Question 3

What is the management of SIADH?

Answer 3

If mild / asymptomatic – fluid restriction

If symptomatic

• Fluid restriction
• Loop diuretics (eg: Furosemide)
• +/- ADH Receptor Antagonist (Demeclocycline) OR Vasopressin Antagonists (Vaptans eg: Conivaptan & tolvaptan)

Question 4

What are the key biochemical factors of 21β-hydroxylase deficiency?

Answer 4

Hypocortisolism

• Hypotension
• HypoNa
• Hypoglycaemia
• Hyperpigmentation

↓ Aldosterone & DOC = ↓ Mineralocorticoid Activity

• HypoNa
• HyperK
• Metabolic Acidosis

Hyperandrogenism

• Females: Ambiguous Genitalia (Clitomegaly, Male external genitalia), Virilisation, Oligomenorrhea, Infertility
• Males & Females: Precocious Puberty (for females is due to peripheral aromatisation of excess androgens to estrogen)

Question 5

What is the management of 21β-hydroxylase deficiency?

Answer 5

Cortisol supplementation

Fludrocortisone supplementation

Question 6

What is the management of 11β-hydroxylase deficiency?

Answer 6

Hypocortisolism

• Hypoglycaemia
• Hyperpigmentation

↓ Aldosterone & ↑ DOC = ↑ Mineralocorticoid Activity

• HTN
• HyperNa
• HypoK
• Metabolic Alkalosis

Hyperandrogenism

• Females: Ambiguous Genitalia (Clitomegaly, Male external genitalia), Virilisation, Oligomenorrhea, Infertility
• Males & Females: Precocious Puberty (for females is due to peripheral aromatisation of excess androgens to estrogen)

Question 7

What is the management of 21β-hydroxylase deficiency?

Answer 7

Cortisol supplementation

Spironolactone

Question 8

What is the management of 17α-hydroxylase deficiency?

Answer 8

Hypocortisolism

• Hypoglycaemia
• Hyperpigmentation

↓ Aldosterone & ↑ DOC = ↑ Mineralocorticoid Activity

• HTN
• HyperNa
• HypoK
• Metabolic Alkalosis

Hypoandrogenism
Males: Ambiguous Genitalia (Female External Genitalia), Undescended Testes
- Males & Females: Delayed Puberty

Question 9

What is the management of 17α-hydroxylase deficiency?

Answer 9

Cortisol supplementation

Spironolactone

Estrogen Replacement Therapy for XX Phenotype