Diabetes insipidus its physiology,etiology,clinical picture,investigation and newest treatment

1. Physiology :

a. Hormone : ADH (antidiuretic hormone)[ vasopressin ].

b. Gland : Pituitary gland [ posterior lobe ].

c. Function of the hormone :

i. ↑↑ water reabsorption by renal tubules.

ii. Large dose → v.c. of bl. vessels.

N.B. :

ADH is synthesized in hypothalamus & then transported

along axons & stored in i post. Pituitary.

d. Regulation of this hormone :

i. ↑↑ ADH by :

1. ↑ osmolarity.

2. hypovolemia.

3. stress

4. drugs :

a. nicotine.

b. barbiturates.

ii. ↓↓ ADH by :

1. ↓ osmolarity.

2. hypertension.

3. cold weather.
2. Etiology :

a. Central DI → damage of hypothalmo-hypophyseal axis:

i. Idiopathic : starts in childhood.

ii. Tumor.

iii. Trauma : head injuries & after hypophysectomy.

iv. Granulomas : T.B. & sarcoidosis.

b. Familial DI ( Walfram syndrome) [ DIDMOAD ] hereditary

condition → defect in osmo-receptrs ass. é

i. DI diabetes insipidus.

ii. DM diabetes mellitus

iii. OA optic atrophy

iv. D deafness.

c. Nephrogenic DI ( Renal tubules not responding to ADH )

i. Hereditary .

ii. Acquired : 2ry to :

1. renal tubular acidosis.

2. kidney amyloidosis.

3. hypercalcemia.

4. hypokalemia.

5. drugs :

a. lithium.

b. cholchicine.

3. C / P :

a. C / p of i cause :

i. Surgery → hypophysectomy.

ii. Tumor → ↑ intracranial tension.

b. C / p of i hormone :

i. Polyuria & nocturia : 5 – 20 L/day.

ii. Dehydration , polydepsia,

weight loss & low grade fever.

iii. Hypovitamonosis : of water soluble vitamins.

iv. Complications : shock.

4. Differential diagnosis :

Other causes of polyuria. [discussed later].

_ especially ; psychogenic polydepsia.

N.B. :

_ DI :

- polyuria → polydepsia.

- so ; there is ↑↑ osmolarity.

_ Psychogenic polydepsia :

- polydepsia → polyuria .

- so ; there is ↓↓ osmolarity.

5. Investigation :

a. Inv. for i cause :

i. Imaging for i gland :

1. X-ray.

2. C.T. & M.R.I.

b. Assay of i hormone level :

i. In blood.

ii. In urine.

c. Inv. of i function of i hormone :

i. Urine analysis :

1. Polyuria é no pathological constitutes.

2. Specific gravity : low.

3. After fluid deprivation : - polyuria persists.

& - Sp.G. fails to rise.

ii. Plasma osmolarity

_ ↑↑ due to loss of free water é high plasma Na.

d. Tests for localization of i cause :

i. Test i hypothalamus :

_ material : nicotine.

smoking cigarette or inject 1-3 ml nicotine.

1. normal : oliguria.

2. in case of central DI : no change.

ii. Test osmo-receptrs :

_ material : I.V. hypertonic saline

( NaCl 2.5 % ) .

1. normal : oliguria.

2. if i lesion is in osmo-receptrs ( e.g. familial DI ) :

no change.

iii. Test kidney : [ to ( ) central DI & nephrogenic DI ]

_ material : vasopressin. [ test _

1. in central DI : oliguria.

2. in nephrogenic DI : no change.

6. Treatment :

a. TTT of i cause.

b. Diet : excess fluid, salts, fats, CHO & vitamins.

c. Replacement therapy :

_ Desmopressine ( synthetic ADH )

nasal spray ; twice daily.

d. Drugs :

_ Cholropropamide & Carbemazepine ( tegretol )

may be used in nephrogenic DI both sensitizerenal tubules to ADH.see the pictures