Both, Diabetes Mellitus and Diabetes Insipidus, sound the same, since both conditions give rise to excessive thirst and polyuria, but they are entirely two different entities with regard to the pathogenesis, investigations, complications and management.
It is a clinical syndrome characterized by hyperglycemia due to absolute or relative deficiency of insulin and being categorized into four sub groups namely Type I, II, III, and IV, according to their etiology.
Type I results from autoimmune destruction of the pancreas which is most commonly seen in young age while type II is of adult onset mostly resulting from insulin resistance. Diabetes acquired secondary to some other disease such as genetic defects of beta cell function, pancreatic diseases, drugs induced causes, viral infections are categorized as type III while gestational diabetes is type IV.
Clinical features include polydypsia, polyuria, nocturia, weight loss, blurring of vision, pruritis vulvae, hyperphagia etc.
The metabolic derangements seen in diabetes mellitus are frequently associated with long term macro and micro vascular complications resulting in diabetes nephropathy, neuropathy and peripheral vascular disease. The medical emergencies encountered are diabetic ketoacidosis and hyper osmolar non ketotic coma.
Management of type I diabetes is solely insulin, while Type II includes dietary control and oral hypoglyceamic agents, in addition to insulin.
According to the etiology of diabetes insipidus, it can be categorized as cranial diabetes insipidus and nephrogenic diabetes insipidus. In cranial diabetes insipidus, there is deficient production of ADH by the hypothalamus, and in nephrogenic diabetes insipidus, the renal tubules are unresponsive to ADH.
The cranial causes include structural hypothalamic or high stalk lesions, idiopathic or genetic defects and the nephrogenic causes include genetic defects, metabolic abnormalities, drug therapy, poisoning and chronic kidney diseases.
Diagnosis is confirmed in the phase of elevated plasma osmolality (>300 mOsm/kg), either ADH is not measurable in serum or urine is not maximally concentrated (<600 mOsm/kg), and by water deprivation test.
Treatment is with desmopressin/DDAVP, an analog of ADH with a longer half life. Polyuria in nephrogenic diabetes is improved with thiazide diuretics and NASIDs.
What is the difference between Diabetes Mellitus and Diabetes Insipidus?
• Diabetes mellitus is a common condition while the other is uncommon.
• Diabetes mellitus is a multi systemic disorder affecting almost all the systems of the body.
• Diabetes mellitus causes polyuria via osmotic diuresis, while polyuria in diabetes insipidus is caused by failure in ADH secretion or failure, in its action on the renal tubules.
• Management of diabetes includes dietary control, oral hypoglycemic agents and insulin while diabetes insipidus includes desmopressin/DDAVP.