I. Definition/etiology
A. A grouping of symptoms that result from secretion of antidiuretic hormone (ADH) independent of volume-dependent stimulation or osmolality
B. ADH is released from the posterior pituitary gland or from malignant tumors; this results in severe water retention despite a low serum osmolality.
II. Incidence/predisposing factors/etiology
A. Affects 1% to 2% of patients with cancer
B. Central nervous system disorders such as brain tumors, hemorrhages, head trauma (including skull fractures), meningitis, Guillain-Barré syndrome, and systemic lupus erythematosus may occur first.
C. Chronic lung disease, including chronic obstructive pulmonary disease and tuberculosis, bacterial pneumonia, aspergillosis, and bronchiectasis, may be causative.
D. Malignancies such as bronchogenic, pancreatic, prostatic, and renal carcinoma, leukemia, and malignant lymphoma may precede the syndrome.
E. Pharmacologic agents that increase ADH production or potentiate ADH action such as antidepressants, NSAIDs, and carbamazepine (Tegretol) may predispose patients to the condition.
III. Subjective/physical examination findings
A. Neurologic changes from hyponatremia (mild headache to seizures)
B. Hypothermia may be present.
C. Concentrated urine (ADH stimulates kidneys to reabsorb water)
D. Decreased urinary output
E. Decreased deep tendon reflexes
F. Weight gain and edema
G. Vomiting and abdominal cramping
H. Thyroid, cardiac, renal, adrenal, and liver function are not affected by the disease.
IV. Diagnostic/laboratory findings
A. Hyponatremia—Yet the patient is euvolemic.
B. Decreased serum osmolality (less than 280 mOsm/kg)
C. Increased urine osmolality (greater than 150 mOsm/kg)
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