Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) Clinical Presentation

Updated: Aug 04, 2021
  • Author: Christie P Thomas, MBBS, FRCP, FASN, FAHA; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Depending on the magnitude and rate of development, hyponatremia may or may not cause symptoms.Consequently, the syndrome of inappropriate antidiuretic hormone secretion.(SIADH). is usually detected by laboratory testing.

In general, slowly progressive hyponatremia is associated with fewer symptoms than is a rapid drop of serum Na+ to the same value. Patients with moderate, chronic hyponatremia may have decreased reaction times, cognitive slowing, and ataxia resulting in frequent falls. [19, 22]

Signs and symptoms of acute hyponatremia do not precisely correlate with the severity or the acuity of the hyponatremia. Some patients with profound hyponatremia may be relatively asymptomatic. Anorexia, nausea, and malaise are early symptoms and may be seen when the serum Na+ level is less than 125 mEq/L. A further decrease in the serum Na+ level can lead to headache, muscle cramps, irritability, drowsiness, confusion, weakness, seizures, and coma. These occur as osmotic fluid shifts result in cerebral edema and increased intracranial pressure.

Important considerations related to the history are symptoms that reflect the cause of SIADH. Patients may have symptoms that suggest increased secretion of ADH, such as chronic pain, symptoms from CNS or pulmonary tumors (eg, hemoptysis, chronic headaches), or head injury, and drug use. It is important to determine if the patient has had excessive fluid intake because of inappropriate thirst or psychogenic polydipsia or because hypotonic fluids were administered in a healthcare setting. The history may also give important information about the chronicity of the condition, which may, in turn, influence the rate of correction of hyponatremia.


Physical Examination

After the identification of hyponatremia, the approach to the patient depends on the clinically assessed volume status. In SIADH, the patient is typically euvolemic and normotensive. Peripheral and pulmonary edema, dry mucous membranes, reduced skin turgor, and orthostatic hypotension are usually absent. Edema in a hyponatremic patient warrants consideration of another hyponatremic state, such as congestive heart failure (CHF), cirrhosis, or chronic kidney disease.

Prominent physical examination findings may be seen only in severe or rapid-onset hyponatremia and can include the following:

  • Confusion
  • Disorientation
  • Delirium
  • Generalized muscle weakness
  • Myoclonus
  • Tremor
  • Asterixis
  • Hyporeflexia
  • Ataxia
  • Dysarthria
  • Cheyne-Stokes respiration
  • Pathologic reflexes
  • Generalized seizures
  • Coma