Diabetes Insipidus

Overview

Diabetes insipidus (DI) is a rare disease presenting mainly passage of large volumes of dilute urine. This is followed by polydipsia. There is an inability to produce a concentrated urine. It is caused by a deficiency of anti-diuretic hormone (ADH) or resistance to anti-diuretic hormone

Signs and Symptoms

Polydipsia (Intense thirst & drinking vast quantities of water), Polyuria (>3 litres/day), Nocturia, Symptoms of hypernatraemia (Lethargy, confusion, coma, fits), Reduced skin turgor, Dry mucous membranes, Possible hypotension / tachycardia, Sunken eyeballs, Possible confusion, Fits/Seizures, Coma

Common Causes

Idiopathic (30%), Head trauma, Pituitary surgery, Crainiopharyngioma, Infiltrative e.g. sarcoid, CNS infections (meingitis/encephalitis), Autoimmune, Hypoxic or ischaemic encephalopathy, Rare familial causes e.g. Wolfram syndrome, Hereditary causes (90% are X-linked), Drugs e.g. lithium, Metabolic e.g. hypercalcaemia, Myeloma/amyloid, Sjogren's syndrome, Sickle cell anaemia, Chronic kidney disease, Post obstructive uropathy

Investigation Techniques

8 hour water deprivation test (Aims to test ability of the kidneys to concentrate urine for the diagnosis of DI & to localise the cause), 24 hour urinary volume, Plasma and urine osmolality, Thirst response, U&E (Na+ can be normal or high in D.I.), Glucose (to out rule diabetes mellitus), Calcium, MRI Pituitary (aetiology), Pituitary function test (aetiology), Lithium levels/toxicology screen (aetiology), Renal imaging e.g. renal ultrasound (aetiology)

Treatment and Prevention

Central DI - Partial DI and mild to moderate polyuria and nocturia may be adequately controlled with a low-solute diet (if acceptable to the patient) and a thiazide diuretic. Although these modalities also reduce the urine output in patients desmopressin therapy is usually required for symptom control. Desmopressin can also be used in patients with less severe DI who do not want to comply with a low-solute diet, Nephrogenic - the urine output can be lowered with a low-salt/low-protein diet/diuretics, and nonsteroidal anti-inflammatory drugs (NSAIDs). In infants early recognition is of immediate clinical significance because treatment can avert the physical and mental retardation that results from repeated episodes of dehydration and hypernatremia.