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Diabetes Insipidus

Background Knowledge ๐Ÿง 

Definition

  • A disorder characterised by an inability to concentrate urine, leading to polyuria and polydipsia.
  • Caused by either a deficiency of antidiuretic hormone (ADH) or a renal insensitivity to ADH.
  • Divided into central (neurogenic) and nephrogenic types.

Epidemiology

  • Central DI is more common than nephrogenic DI.
  • Affects males and females equally.
  • Can occur at any age, but central DI often presents in childhood or young adulthood.
  • Nephrogenic DI can be congenital or acquired.
  • Rare condition overall.

Aetiology

  • Central DI: Caused by damage to the hypothalamus or pituitary gland, leading to ADH deficiency.
  • Nephrogenic DI: Caused by renal insensitivity to ADH, often due to genetic mutations or drugs (e.g. lithium).
  • Other causes include head trauma, tumours, infections, and autoimmune conditions.

Pathophysiology

Lack of ADH action leads to inability of kidneys to concentrate urine, resulting in excessive water loss and dehydration.

Clinical Features ๐ŸŒก๏ธ

Symptoms

  • Polyuria (excessive urination)
  • Polydipsia (excessive thirst)
  • Nocturia (waking up at night to urinate)
  • Dehydration
  • Fatigue
  • Headache
  • Dry skin and mucous membranes

Signs

  • Signs of dehydration (e.g., dry mucous membranes, reduced skin turgor)
  • Hypotension
  • Tachycardia
  • Hypernatraemia (if fluid intake is inadequate)
  • Low urine osmolality
  • High serum osmolality
  • Large volumes of dilute urine

Investigations ๐Ÿงช

Investigations

  • Water deprivation test (to differentiate between central and nephrogenic DI)
  • Desmopressin (DDAVP) test
  • Serum electrolytes and osmolality
  • Urine osmolality
  • MRI of the brain (to identify pituitary or hypothalamic pathology)
  • Genetic testing (if congenital nephrogenic DI is suspected)
  • 24-hour urine volume measurement

Management ๐Ÿฅผ

Management

  • Central DI: Desmopressin (DDAVP) replacement therapy.
  • Nephrogenic DI: Thiazide diuretics, low-salt diet, and NSAIDs.
  • Adequate hydration to prevent dehydration.
  • Monitor serum sodium and osmolality regularly.
  • Treat underlying cause if identified (e.g. tumour removal).
  • Patient education on condition management and emergency measures.

Complications

  • Dehydration and electrolyte imbalances
  • Hypernatremia
  • Hypotension
  • Kidney damage (if chronic and untreated)
  • Severe dehydration can lead to shock
  • Increased risk of urinary tract infections
  • In rare cases, death if not managed appropriately

Prognosis

  • With proper treatment, patients can lead normal lives.
  • Lifelong treatment is often necessary for central DI.
  • Prognosis for nephrogenic DI depends on the underlying cause.
  • Regular monitoring and patient compliance with therapy are crucial.
  • Patient education on fluid management and medication use is essential.
  • Complications can be minimised with appropriate treatment.

Key Points

  • Diabetes insipidus is characterised by polyuria and polydipsia due to ADH deficiency or insensitivity.
  • Differentiation between central and nephrogenic DI is essential for appropriate management.
  • Management includes hormone replacement, lifestyle changes, and treatment of underlying causes.
  • Regular monitoring and patient education are critical to prevent complications.
  • With proper management, patients can lead normal lives.

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