Diabetes Insipidus Flashcards
what is the definition of DI?
Diabetes insipidus is a metabolic disorder characterised by an absolute or relative inability to concentrate urine, resulting in the production of large quantities of dilute urine Diabetes insipidus (DI) may be central in origin, resulting from an absolute or relative deficiency of arginine vasopressin (AVP); or it may be nephrogenic in origin, resulting from a renal insensitivity or resistance to AVP.
what is the epidemiology of DI?
Rare
Central DI most common
what is the aetiology of DI?
Can be genetic or acquired
Central DI:
Pituitary surgery, craniopharyngioma, post traumatic head injury, congenital malformation of pituitary or hypothalamus, wolfram syndrome
Nephrogenic DI:
Medications, systemic disease, mutations in AVPR2 receptor, aquaporin-2 mutations
Pregnancy
what are the risk factors for DI?
Pituitary surgery craniopharyngioma pituitary stalk lesion traumatic brain injury congenital pituitary abnormalities medications autoimmune diseases family history Pregnancy, subarachnoid haemorrhage, renal sarcoidosis, renal amyloidosis
what is the pathophysiology of DI?
Central DI results from any condition that impairs the production, transportation, or release of AVP.
Nephrogenic DI results from conditions that impair the renal collecting ducts’ ability to respond to AVP.
Both central and nephrogenic DI are characterised by impaired renal water reabsorption, resulting in the production of excessive, hypotonic (dilute) urine (polyuria), in volumes ranging from 3 litres to >20 litres per day. This is accompanied by significant thirst and increased drinking (polydipsia), as central osmo-sensing and peripheral baro-sensing drive central thirst and thirst-dependent behaviours to maintain circulating volume and osmolar status.
Patients with DI due to a non-traumatic aetiology generally have an insidious onset of symptoms. Patients with central DI following traumatic brain injury or pituitary surgery typically experience a more rapid onset of symptom
what are the key presentations of DI?
History of pituitary or hypothalamic disease Family history History of lithium therapy History of autoimmune disease Polyuria Increased thirst
what are the signs of DI?
History of pituitary or hypothalamic disease Family history History of lithium therapy History of autoimmune disease Signs of volume depletion
what are the symptoms of DI?
Polyuria / nocturia
Polydipsia
Visual field defects
Focal motor deficits
what are the first line and gold standard investigations for DI?
Urine osmolality - low
Serum osmolality - elevated
Serum glucose - normal
Serum sodium - elevated
Serum potassium - low
Serum urea nitrogen - elevated
Serum calcium - elevated
Urine dipstick - negative for glycosuria, proteinuria if underlying renal disease
24-hour urine collection for volume (confirmatory of DI)- >3L in 24hrs
Water deprivation test (distinguishes between central and nephrogenic) - urine osmolality <300 mmol/kg (<300 mOsm/kg) with corresponding serum osmolality >290 mmol/kg (>290 mOsm/kg)
AVP stimulation test - central DI: reduction in urine output and increase in urine osmolality to >750 mmol/kg (>750 mOsm/kg); nephrogenic DI: little or no reduction in urine output and no increase in urine osmolality
Hypertonic saline-stimulated test with measurement of copeptin (differentiate between primary polydipsia and DI) - baseline copeptin level >21.4 picomol/L is diagnostic of nephrogenic DI; copeptin level >4.9 picomol/L differentiates central DI from primary polydipsia
what are the differential diagnoses for DI?
Psychogenic polydipsia, DM, diuretic use, hypercalcaemia
how is DI managed?
In hypernatraemia - oral / IV fluids
Acute central - desmopressin, oral/IV fluids
Chronic central - desmopressin
Nephrogenic - maintenance of adequate fluid intake, treatment of underlying cause, sodium restriction
how is DI monitored?
Patients require regular follow-up with monitoring of serum electrolytes to assess sodium status.
For patients with central DI, follow-up imaging is recommended if initial scans were unable to detect pathology, as pituitary, para-pituitary, or stalk lesions may not manifest on initial scanning.
In patients with nephrogenic DI for whom polyuria is significant, bladder dysfunction may develop. If unrecognised, this may lead to renal impairment. These patients need periodic renal and bladder ultrasonography and regular assessment of serum creatinine.
what are the complications of DI?
Hypernatremia, thrombosis, bladder and renal dysfunction, iatrogenic hyponatremia
what is the prognosis of DI?
Generally good with treatment, depends on aetiology of DI
