Diabetes Insipidus

Definition

Diabetes Insipidus (DI) is a condition characterised by an imbalance in water regulation in the body, leading to excessive urination (polyuria) and intense thirst (polydipsia). It is caused by either a deficiency of antidiuretic hormone (ADH), also known as vasopressin, or a resistance to its effects in the kidneys.

Aetiology

Diabetes Insipidus can be classified into two main types:

Central Diabetes Insipidus: Caused by a deficiency of ADH due to damage to the hypothalamus or pituitary gland. This can result from head injury, infections, tumours, or genetic disorders.
Nephrogenic Diabetes Insipidus: Caused by the kidneys' inability to respond to ADH. This can be due to genetic mutations, chronic kidney disease, or medications such as lithium.

Pathophysiology

ADH is produced in the hypothalamus and stored in the posterior pituitary gland. It acts on the kidneys to promote water reabsorption, thereby concentrating the urine. In Central DI, a deficiency of ADH leads to decreased water reabsorption and dilute urine. In Nephrogenic DI, the kidneys are unresponsive to ADH, resulting in similar effects. The consequent loss of large volumes of dilute urine leads to dehydration and a compensatory increase in thirst.

Risk Factors

Family history of Diabetes Insipidus
Head injury or brain surgery
Hypothalamic or pituitary tumours
Infections affecting the brain (e.g., meningitis, encephalitis)
Chronic kidney disease
Use of certain medications (e.g., lithium)

Signs and Symptoms

Common signs and symptoms of Diabetes Insipidus include:

Polyuria (excessive urination)
Polydipsia (excessive thirst)
Nocturia (frequent urination at night)
Dehydration
Dry skin and mucous membranes
Fatigue
Electrolyte imbalances

Investigations

Clinical history and physical examination
Serum and urine osmolality: To assess the concentration of solutes in blood and urine
Water deprivation test: To differentiate between types of DI by evaluating the body's ability to concentrate urine in response to dehydration
ADH (vasopressin) levels: To measure the amount of ADH in the blood
Desmopressin (DDAVP) stimulation test: To distinguish between central and nephrogenic DI
Magnetic resonance imaging (MRI): To detect abnormalities in the hypothalamus or pituitary gland

Management

Primary Care Management

Referral to an endocrinologist: For diagnosis confirmation and management plan.
Hydration: Ensuring adequate fluid intake to prevent dehydration.
Monitoring: Regular follow-up to assess symptom control and electrolyte balance.
Education: Informing patients about the condition, the importance of medication adherence, and recognising signs of dehydration.

Specialist Management

Desmopressin (DDAVP): A synthetic analogue of ADH, used in Central DI to reduce urine output and control symptoms.
Thiazide diuretics: Used in Nephrogenic DI to reduce urine output by decreasing the amount of fluid that reaches the kidneys.
Low-salt and low-protein diet: To reduce the workload on the kidneys and decrease urine output in Nephrogenic DI.
Treatment of underlying conditions: Addressing any underlying causes such as infections, tumours, or medication-induced DI.

Example Management for Diabetes Insipidus

A patient diagnosed with Central Diabetes Insipidus presenting with polyuria and polydipsia should be referred to an endocrinologist. Management includes the administration of desmopressin (DDAVP) to reduce urine output and control symptoms. Regular monitoring of fluid intake, urine output, and electrolyte levels is essential. The patient should be educated on the importance of medication adherence and recognising signs of dehydration. Adequate hydration should be maintained, and any underlying conditions contributing to DI should be addressed.

References

NICE. (2024). Diabetes Insipidus: Diagnosis and Management. Retrieved from NICE
NHS. (2023). Diabetes Insipidus. Retrieved from NHS
British Society for Paediatric Endocrinology and Diabetes (BSPED). (2022). Clinical Practice Guidelines for the Management of Diabetes Insipidus. Retrieved from BSPED
American Diabetes Association (ADA). (2021). Diagnosis and Management of Diabetes Insipidus. Retrieved from ADA