SIADH: Syndrome of Inappropriate Antidiuretic Hormone Secretion

Causes of SIADH

SIADH can occur due to several underlying conditions, including:

1. Neurological Causes

• Brain injuries (trauma, stroke, or hemorrhage)

• Infections like meningitis or encephalitis

• Central nervous system disorders such as multiple sclerosis

2. Pulmonary Causes

• Pneumonia

• Tuberculosis

• Chronic obstructive pulmonary disease (COPD)

3. Malignancies

• Small-cell lung carcinoma (most common cause among cancers)

• Pancreatic or prostate cancers

4. Medications

• Antidepressants (SSRIs, TCAs)

• Antipsychotics

• Chemotherapeutic agents like vincristine

Symptoms of SIADH

The symptoms of SIADH largely result from hyponatremia and include:

• Early Symptoms: Nausea, headache, fatigue, and muscle cramps

• Severe Symptoms: Confusion, seizures, decreased consciousness, or even coma

It's important to note that the severity of symptoms often correlates with the rapidity and extent of sodium depletion.

Diagnosis of SIADH

Diagnosing SIADH requires a comprehensive approach that includes:

1. Laboratory Tests

• Serum Sodium: Low levels (<135 mEq/L)

• Urine Osmolality: Elevated (>100 mOsm/kg) despite low serum sodium

• Urinary Sodium Concentration: Typically >30 mEq/L

2. Exclusion of Other Causes

• Thyroid, adrenal, and renal function tests to rule out other potential causes of hyponatremia.

3. Imaging

• Chest X-ray or CT scan to detect underlying malignancies or pulmonary conditions.

Treatment of SIADH

The treatment of SIADH focuses on correcting hyponatremia and addressing the underlying cause:

1. Fluid Restriction

• Limiting fluid intake to 800–1000 mL per day is the cornerstone of treatment.

2. Medications

• Tolvaptan or Conivaptan: Vasopressin receptor antagonists

• Demeclocycline: Reduces kidney responsiveness to ADH

3. Hypertonic Saline

• Used in severe cases of hyponatremia, administered with caution to avoid rapid sodium correction, which can cause osmotic demyelination syndrome.

4. Treat Underlying Causes

• Discontinuing causative medications or managing primary conditions like cancer or infections.

Prognosis and Complications

When identified early, SIADH is often manageable with a good prognosis. However, complications like severe hyponatremia can lead to life-threatening consequences such as brain swelling and neurological deficits.

Prevention of SIADH

While not always preventable, the risk of SIADH can be minimized by:

• Regular monitoring for individuals on medications known to cause SIADH

• Early treatment of underlying conditions such as infections or malignancies

Conclusion

SIADH is a complex condition requiring careful evaluation to diagnose and manage effectively. With prompt treatment, including fluid restriction and medications, patients can recover without significant complications. If you experience symptoms suggestive of SIADH, consult a healthcare provider immediately.