Treatment of nephrogenic diabetes insipidus
The name diabetes insipidus (DI) comes from the Greek word diabetes, which means “to cross”, and the Latin insipidus or “tasteless”. Diabetes insipidus occurs due to problems at two points in the antidiuretic hormone pathway:
- Central nervous system problem (central diabetes insipidus): the hypothalamus fails to synthesise or the pituitary gland does not secrete antidiuretic hormone.
- Kidney problem (nephrogenic diabetes insipidus): the kidneys do not respond.
Nephrogenic diabetes insipidus
Nephrogenic diabetes insipidus occurs when the renal tubules stop responding to the action of antidiuretic hormone.
Action of the antidiuretic hormone (ADH)
Under normal circumstances ADH is responsible for inducing water reabsorption in the distal renal tubules and renal collecting duct, depending on fluid requirements. The inactivity of the antidiuretic hormone results in a lack of distal water reabsorption and, in turn, severe polyuria. So the animal will eliminate large amounts of low-density and low-osmolarity urine. The end result is compensatory polydipsia.
What is the aetiology of nephrogenic diabetes insipidus?
Although congenital nephrogenic diabetes insipidus exists, nephrogenic diabetes insipidus is typically due to secondary causes such as chronic kidney failure, pyelonephritis, hypercalcaemia, hypokalaemia, hyperadrenocorticism, hyperthyroidism, pyometra and liver failure.
Clinical signs of nephrogenic diabetes insipidus
Besides polyuria and polydipsia, animals with nephrogenic diabetes insipidus present nocturia, urinary incontinence, weight loss due to anxiety about drinking water. They may also have other associated signs, depending on the underlying aetiology.
Treatment
The aim of nephrogenic diabetes insipidus treatment is to balance the body’s water levels. The volume of fluid ingested must equal the patient’s fluid output. If the patient has a metabolic imbalance, such as hypercalcaemia, then firstly this must be corrected, otherwise diuretics will not resolve the problem.
A low-salt, low-protein diet must be followed during treatment.
Nephrogenic diabetes insipidus is treated with diuretics, particularly those belonging to the thiazides family. They reduce sodium reabsorption, so more is eliminated in urine and therefore blood sodium levels fall. Lowering plasma sodium decreases water intake, which, in turn, reduces urine output. Chlorothiazide and hydrochlorothiazide are often used.
