Syndrome Inappropriate ADH

About Your Diagnosis
Antidiuretic hormone (ADH) is an important hormone in maintaining normal water balance. Too little ADH results in diabetes insipidus, which is manifested by large volumes of water in the urine. Too much ADH results in the syndrome of inappropriate antidiuretic hormone secretion (SIADH), with water retention and decreased blood sodium levels. Many different conditions and drugs may cause SIADH. Antidiuretic hormone may be produced by certain tumors such as a lung cancer, or may result from chronic lung diseases. A long list of medicines has been associated with SIADH including such common medicines as antidepressants, antianxiety agents, antipsychotic agents, seizure medicines, and desmopressin (DDAVP).
Many individuals have a mild form of SIADH that causes no symptoms. More advanced cases with markedly decreased serum sodium levels usually occur in hospitalized patients who are undergoing surgical procedures or being treated for brain tumors, seizure disorders, lung cancers, or other chronic conditions. The diagnosis is established through a combination of blood and urine tests performed under certain specified conditions. The patient must not be dehydrated or volume overloaded. The patient must have a low serum sodium and plasma osmolality level, and an inappropriately concentrated urine (increased urine osmolality level) to have SIADH diagnosed. These tests indicate an excess of body water relative to the amount of body sodium. In other words, ADH is inappropriately holding onto too much water. It is important to eliminate other causes of a low sodium level, such as hypothyroidism or adrenal insufficiency, before settling on a diagnosis of SIADH. Curing SIADH is possible by removing the offending drug or tumor, and by treating the underlying condition.

Living With Your Diagnosis
Early SIADH has no symptoms; however, if left untreated, SIADH may cause lethargy, weakness, seizures, and coma. Symptoms are worse in those
patients whose serum sodium levels fall rapidly. Most individuals tolerate SIADH well with no effects. However, it may progress to coma and death
if untreated.

Treatment
Water restriction is the cornerstone of treatment. Decreased water intake allows the serum sodium level to rise normally. The maximum amount of water that patients with SIADH are allowed to drink is just slightly more than the amount of urine they produce. Patients must have regular serum sodium measurements to ensure that the water restriction has been effective. Some patients may require a diuretic such as furosemide if further treatment is needed. Another medicine called demeclocycline is also effective for SIADH. The most concerning potential side effect from treatment is dehydration. This occurs when water restriction is maintained in a patient with increased fluid requirements because of fever, exercise, or
other reasons. Therapy with furosemide may lead to a low blood potassium level, which, if not corrected, can cause cardiac arrhythmias. Demeclocycline causes a nephrogenic diabetes insipidus (kidney resistance to ADH). Kidney function must be carefully monitored in patients receiving this medicine.

The DOs
• Restrict the amount of water you drink if you have SIADH. This may be the only treatment necessary.
• Understand the reason for your SIADH. If you treat the underlying cause, the SIADH will go away.
• Ask your doctor to eliminate any medicines that may be causing SIADH, whenever possible.
• Follow-up regularly for serum sodium measurements.

The DON’Ts
• Don’t assume you have SIADH just because you have a low blood sodium level. Other disorders must be excluded first.
• Don’t take medication for SIADH unless absolutely necessary. Careful water restriction is a better treatment.

When to Call Your Doctor
• You feel weak or lethargic.
• You have an illness with a fever.
• You are scheduled for elective surgery or a radiologic procedure.