Difference Between Diabetes Insipidus and SIADH

Differences Diabetes Diagnosis & Treatment

Water control diseases that affect the secretion or activity of anti-diuretic hormone (ADH) include Diabetes Insipidus (DI) and the Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH).

Significant electrolyte imbalances and water retention are hallmarks of SIADH, which results from the lack of suppression of Antidiuretic hormone. Both decreased synthesis of Antidiuretic hormone (central DI) and normal Antidiuretic hormone secretion with resistance in the kidneys to its effects constitute Diabetes insipidus (DI) (nephrogenic Diabetes insipidus). Diabetic insipidus causes excessive urination because the body is unable to retain water.

What is Diabetes Insipidus?

Diabetes Insipidus is a condition that occurs when the body is unable to regulate its fluid levels properly. It is caused by a deficiency of antidiuretic hormone (ADH), also known as vasopressin, which is responsible for controlling the amount of urine produced by the kidneys. When there is a shortage of ADH, the kidneys are unable to reabsorb water from the urine, resulting in large amounts of dilute urine being produced.

The symptoms of Diabetes Insipidus include excessive thirst, frequent urination, and dehydration. If left untreated, it can lead to complications such as electrolyte imbalances, low blood pressure, and kidney damage.

What is SIADH?

SIADH is a disorder that results in the body producing too much ADH. This causes the kidneys to retain too much water, leading to low sodium levels in the blood (hyponatremia). The most common cause of SIADH is an underlying medical condition, such as lung disease, brain injury, or cancer.

The symptoms of SIADH include nausea, vomiting, headaches, seizures, confusion, and even coma. The treatment for SIADH focuses on correcting the underlying condition causing the disorder and restoring normal sodium levels in the blood.

Differences: Diabetes Insipidus and SIADH

In terms of diagnosis, there are several tests used to differentiate between DI and SIADH. These tests include urine tests, blood tests, and fluid deprivation tests.

In a urine test, the concentration of the urine is measured to determine if it is dilute or concentrated. In DI, the urine is dilute, while in SIADH, the urine is concentrated.

In a blood test, the levels of ADH and sodium are measured. In DI, the ADH levels are low, while in SIADH, the ADH levels are high. In terms of sodium levels, DI results in high sodium levels, while SIADH results in low sodium levels.

Finally, the fluid deprivation test is used to determine how the body responds to a period of water deprivation. In DI, the body continues to produce large amounts of dilute urine, while in SIADH, the body retains water and produces small amounts of concentrated urine.

The following table highlights the major differences between Diabetes Insipidus and SIADH −

Characteristics	Diabetes Insipidus	SIADH
Definition	It is a medical condition or disorder of water and salt metabolism marked by heavy urination and intense thirst.	SIADH means Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH). This disorder is characterized by an increased and unsuppressible release of ADH either from an abnormal non- pituitary source and posterior pituitary gland. Unsuppressed Antidiuretic hormone causes an unrelenting elevation in solute-free water getting returned by the tubules of the kidney to the venous circulation.
Causes	Kidneys are not receptive to antidiuretic hormone secretion (ADH) Tumour Harm to the hypothalamus and/or the pituitary gland Brain damage or trauma through head injury or stroke Complications that happen during pituitary surgery or brain Drugs like Declomycin. This drug inhibits ADH production.	Mental status changes Nausea, vomiting, Coma, Cerebral oedema, seizures Liver disease Hypothyroidism Adrenal insufficiency Eco-topic tumour production Pulmonary disease/lung cancer Guillain-Barré syndrome (a medical condition that is reversible which impacts the nerves in the body. Guillain- Barré syndrome can lead to muscle pain, weakness, and even temporary paralysis of the chest, facial, and leg muscles. Paralysis of the chest muscles can lead to breathing disorders)
Symptoms	Too much thirst Increased urge too pee during the night Cravings for cold drinks Producing huge amounts of diluted urine	Vomiting or nausea Depressed mood, memory impairment Tremors or cramps Irritability Seizures Personality changes, such as confusion, combativeness, and hallucinations Coma or stupor
Diagnosis Methods	Physical examination Urine analysis Medical history Water deprivation test (to find out how much urine is passed) Assessment of electrolyte levels – Blood tests Computed tomography (CT) scans. Magnetic resonance imaging (MRI) scan of the brain	Biochemistry tests to find out serum sodium level Urine osmolality (random sample collected at same time as serum sample) Serum osmolality Thyroid function tests Early morning cortisol level Computed tomography (CT) of the head in case of a neurosurgical condition (example subdural haematoma, subarachnoid haemorrhage) Chest X-ray in case SIADH is caused due to pulmonary reasons.
Treatment	Treatment choices for the common types of diabetes insipidus are discussed below: Central diabetes insipidus: This treatment involves treatment with a man-made hormone known as desmopressin (DDAVP, Minirin, others). This medicine replaces the missing ADH (anti-diuretic hormone) and bring down peeing capacity. Other medications are also prescribed, such as chlorpropamide and indomethacin (Tivorbex, Indocin). These medications can make anti- diuretic hormone (ADH) more available in the body. Nephrogenic diabetes insipidus: In this treatment, doctors will prescribe a low-salt diet to assist in decreasing the amount of urine the kidneys make. Drinking enough water to avoid dehydration is also recommended. Medicines like hydrochlorothiazide (Microzide) helps in improving the symptoms. Gestational diabetes insipidus − Treatment for gestational diabetes insipidus is with the synthetic hormone desmopressin. Primary polydipsia This kind of treatment involves decreasing the intake of fluid. If Primary polydipsia is related to a mental illness, treatment and addressing the mental	Drugs for treatment include − Demeclocycline – the most potent inhibitor of Vasopressin (ADH/AVP) action. An antagonist of the V2 vasopressin receptor -Tolvaptan An antagonist of both V1A and V2 vasopressin receptors – Conivaptan illness will help in relieving the diabetes insipidus symptoms. Diuretic − Increases urine production to remove excess water and salt.

Conclusion

In conclusion, Diabetes Insipidus and SIADH are two distinct disorders that affect the body's fluid and electrolyte balance. While they share some similarities, such as excessive thirst and frequent urination, their underlying causes and treatment options are vastly different. It is important to seek medical attention if you experience any symptoms associated with these disorders to receive proper diagnosis and treatment.

Vineet Nanda

Updated on: 04-Apr-2023

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