Syndrome of Inappropriate Antidiuretic Hormone Secretion
A potentially life-threatening condition, syndrome of inappropriate antidiuretic hormone (SIADH) secretion is marked by excessive release of antidiuretic hormone (ADH), which disturbs fluid and electrolyte balance. SIADH occurs secondary to diseases that affect the osmoreceptors (supraoptic nucleus) of the hypothalamus. The prognosis depends on the underlying disorder and the patient’s response to treatment.
Causes
Usually, SIADH results from oat cell carcinoma of the lung, which secretes excessive ADH or vasopressor-like substances. Other neoplastic diseases (such as pancreatic and prostatic cancers, Hodgkin’s disease,
and thymoma) may also trigger SIADH. Additional causes include:
and thymoma) may also trigger SIADH. Additional causes include:
central nervous system (CNS) disorders, including brain tumor or abscess, cerebrovascular accident, head injury, and Guillain-Barré syndrome
pulmonary disorders (such as pneumonia, tuberculosis, lung abscess) and positive-pressure ventilation
drugs (for example, chlorpropamide, tolbutamide, vincristine, cyclophosphamide, haloperidol, carbamazepine, clofibrate, morphine, and thiazides)
endocrine disorders, such as adrenal insufficiency, myxedema, and anterior pituitary insufficiency.
Complications
Without prompt treatment, SIADH may lead to water intoxication, cerebral edema, and severe hyponatremia, with resultant coma and death.
Assessment
The patient’s medical and medication histories may provide a clue to the cause of SIADH. A history of cerebrovascular disease, cancer, pulmonary disease, or recent head injury is especially significant.
Most commonly, a patient with SIADH complains of anorexia, nausea, and vomiting. Despite these symptoms, the patient may report weight gain. The patient or family may also report CNS symptoms, such as lethargy, headaches, and emotional and behavioral changes.
Inspection usually fails to reveal edema because much of the free water excess is within cellular boundaries. Palpation may detect tachycardia associated with increased fluid volume. Neurologic assessment may detect disorientation, which may progress to seizures and coma. Examination findings may also include sluggish deep tendon reflexes and muscle weakness.
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