What is SIADH?

It is the opposite of Diabetes Insipidus. The body makes too much ADH, causing the kidneys to hold onto water. This dilutes the sodium in the blood (Hyponatremia).

Causes:

• Lung Problems: Pneumonia, small cell lung cancer.
• Brain Problems: Meningitis, stroke, head trauma.
• Medications: SSRIs (antidepressants), carbamazepine, ecstasy.
• Post-Surgery.

Symptoms (from Low Sodium):

• Mild: Nausea, headache, confusion.
• Severe: Seizures, coma (if sodium drops very low, very quickly).

Diagnosis:

• Low Serum Sodium (<135 mEq/L).
• Low Serum Osmolality (dilute blood).
• Inappropriately Concentrated Urine (the kidneys should be peeing out dilute urine to correct the problem, but they're not).
• High Urine Sodium.

Treatment:

• Treat the Underlying Cause (e.g., stop the offending medication, treat pneumonia).
• Fluid Restriction: Limit water intake to <1 liter/day.
• Salt Tablets.
• Vaptans (Tolvaptan, Conivaptan): Medications that block ADH receptors. Used for severe or chronic SIADH.

Warning:

Correcting sodium too quickly can cause Osmotic Demyelination Syndrome (brain damage). Sodium must be raised slowly in the hospital.