DIABETES INSIPIDUS AND NEUROLOGICAL DISORDERS

DIABETES INSIPIDUS AND NEUROLOGICAL DISORDERSDR. SUMIT KAMBLESR NEUROLOGYGMC. KOTA

Decreased secretion or action of AVP

Syndrome characterized by the production of abnormally large volumes of dilute urine. 24-hour urine volume is >50 mL/kg body weight, and osmolarity is 300 mosmol/L, specific gravity >1.010) before body weight decreases by 5% or plasma osmolarity/sodium rise above the upper limit of normal, patient has severe pituitary or severe nephrogenic DI.These disorders usually can be distinguished by administering desmopressin (0.03 g/kg SC or IV) and repeating the measurement of urine osmolarity 12 hours later. An increase of >50% indicates severe pituitary DI, whereas a smaller or absent response is strongly suggestive of nephrogenic DI.

6. Plasma and urine ADH measurement Plasma or urine samples collected at baseline and following water deprivation should be sent for measurement of ADH :If there is an increase in plasma or urine ADH in response to the rising plasma osmolality, central DI is excluded.If there is an appropriate elevation in urine osmolality as ADH secretion is increased, nephrogenic DI is excluded.

MRI of Pituitary and HypothalamusIn most healthy adults and children, posterior pituitary emits a hyperintense signal in T1-weighted midsagittal images. This bright spot is almost always present in patients with primary polydipsia but is invariably absent or abnormally small in patients with pituitary DI. It is usually also small or absent in nephrogenic DI presumably because of high secretion and turnover of AVP.

Treatment of central diabetes insipidusDesmopressin, which is an ADH analog and is preferred drug in almost all patients.Other drugs -chlorpropamide,carbamazepine, thiazide diuretics, and non steroidal antiinflammatory drugs.A low solute (mostly low sodium, low protein) diet.

Initial aim of therapy is to reduce nocturia.Once this is achieved, aims forpartialcontrol of the diuresis during the day.

DESMOPRESSINDesmopressin (DDAVP) is synthetic analogue of AVPActs selectively at V 2 receptors to increase urine concentration and decrease urine flow in a dose-dependent mannerMore resistant to degradation than is AVP and has a three- to fourfold longer duration of action.Preparations- can be given by IV or SC injection, nasal inhalation, or oral tablet. Doses - 12 g qd or bid by injection, 1020 g bid or tid by nasal spray, or 100400 g bid or tid orally.

Onset of action is rapid, ranging from as little as 15 minutes after injection to 60 minutes after oral administration.Safeduring pregnancy for both the mother and the fetus

Thiazide diuretics, Chlorpropamide, carbamazepine , clofibrate, and nonsteroidal antiinflammatory drugsIncrease ADH release or enhance ADH effect on the kidneyAssociated with more side effects than desmopressin and are generally less effective.Lower urine output by 25 to 60%

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REFERENCES-Uptodate.com

Harrisons principles of internal Medicine. 19th edition

Maghnie M, Cosi G, Genovese E, et al. Central diabetes insipidus in children and young adults. N Engl J Med 2000; 343:998.