A 60-year-old man with small cell carcinoma of lung is rushed to emergency room in coma after suffering a clonic-tonic seizure. Patient's temperature is 37degC , blood pressure 100/50 mm Hg and pulse is 88 per minute. Laboratory studies show a serum sodium of 103 mmol/L, normal serum levels of BUN & creatinine and a dilute but otherwise normal urine. A CT scan of the head is normal. Which of the following is the most likely cause of seizures in this patient?
- Given clinical features suggests the diagnosis of syndrome of inappropriate ADH (SIADH) secretion. SIADH - Associated with ADH excess, which causes resorption of excessive amount of free water, resulting in hyponatremia. - Causes of SIADH Secretion of ectopic ADH by malignant neoplasms (small-cell carcinomas of lung, intracranial neoplasms); Non-neoplastic diseases of lung Local injury to hypothalamus / neurohypophysis. - C/F- Hyponatremia, cerebral edema & neurologic dysfunction. - Cardinal features- Marked | in both serum sodium & osmolality | Urine osmolality. - Although total body water is increased, blood volume remains normal & peripheral edema does not develop. Diabetes mellitus may cause polyuria, glucosuria and does not cause severe hyponatremia. Diabetes insipidus - ADH deficiency causes diabetes insipidus, a condition characterized by excessive urination (polyuria) due to an inability of the kidney to resorb water properly from the urine, can occur in a variety of conditions, including head trauma, CNS tumors, inflammatory disorders of the hypothalamus and pituitary, and surgical complications.
Central diabetes insipidus
Diabetes mellitus
Renal metastases
Syndrome of inappropriate ADH secretion
Miscellaneous