A CASE OF HYPONATREMIA DUE TO PITUITARY METASTASIS OF LUNG CANCER.

Context: Hyponatremia is a common electrolyte abnormality.

Objective: We report a patient who presented with hyponatremia and diagnosed as small cell lung cancer metastatic to hypothalamus and pituitary.

Case report: A 68 year old male patient was admitted with fever and cough and pneumonia was considered. Serum sodium level was 113 mmol/L. Syndrome of inappropriate ADH (SIADH) is considered. Thyroid function tests and cortisol levels pointed out a central deficiency in both axes. Pituitary MRI was performed and a hypothalamic and pituitary mass were observed. Prednisolone therapy was started followed by L thyroxine replacement. A chest computer tomography (CT) was taken 2 weeks later revealed a mass lesion. Bronchoscopic biopsy was performed and histopathological diagnosis of the tumor was reported as small cell lung cancer.

Result: Many mechanisms were considered as the cause of hyponatremia in our patient. SIADH, secondary adrenal insufficiency and secondary hypothyroidism due to pituitary metastasis are possible causes.

Conclusion: The reason of hyponatremia is sometimes complex. When the underlying causes of hyponatremia are not evaluated in detail, many diagnoses can be missed.