P-08 Ectopic Cushing Syndrome in a patient with small cell lung cancer

Abstract

Abstract Introduction Ectopic Cushing's syndrome (ECS) is a rare endocrine disorder caused by the autonomous secretion of ACTH from a tumor apart from the hypophysis. ECS is the second most common paraneoplastic syndrome associated with small cell lung cancer (SCLC). Due to the aggressive nature of the syndrome, ECS is difficult to diagnose. Most patients present electrolyte disturbances and muscle weakness rather than the typical clinical features of CS. Clinical Case A 70-year-old female patient hospitalized due to pleural effusion was referred for worsening hyperglycemia. She had no previous history of diabetes mellitus. She had a history of 90 pack-years of smoking and chronic obstructive pulmonary disease. The laboratory results were: fasting plasma glucose 216 mg/dl; creatinine, 0.81 mg/dl; sodium, 138 mmol/l; potassium, 3.1 mmol/l; HbA1c, 8.3%; Arterial blood gas analysis revealed metabolic alkalosis (pH 7.63, HCO3 53.6 meq/L). Due to resistant hypokalemia, the patient was evaluated for CS. The patient's ACTH level was 415.5 pg/ml and cortisol level was 63.44 μg/dl. Table 1 shows the tests perfomed for the diagnosis of CS. Pituitary MRG revealed no pathology. IPSS could not be performed as it is not available at our center. A suspicious mass in the right lung was observed on the thorax CT. The pathology of the cytology sample from the pleural effusion revealed SCLC. A chemotherapy regimen containing cisplatin was initiated. Intravenous potassium and acetazolamide treatment were administered for resistant hypokalemia. However, the patient died one month after diagnosis due to type 2 respiratory failure. Conclusion Ectopic secretion of ACTH accounts for 10–15% of CS. ECS is usually caused by mainly SCLC (45%), thymic carcinoma (15%), bronchial carcinoid (10%) and pancreas islet-cell carcinoma (10%). ECS is reported to occur in 1.6%–4.5% of patients with SCLC. IPSS is the most reliable examination for ECS. For ECS, surgery remains the optimal treatment. Some reports showed that metyrapone, ketoconazole and octreotide are effective but not widely used. In our case, the presence of resistant hypokalemia, metabolic alkalosis, and worsening hyperglycemia with the lack of classic clinical features of CS led us to suspect ECS. ECS has a higher incidence of hypokalemic alkalosis than other causes of Cushing's syndrome (>90% vs. 10%). Excessive amounts of adrenal steroids with the inhibition of the enzyme 11β-hydroxysteroid dehydrogenase may cause this pathology. This enzyme normally converts cortisol to cortisone avoiding the mineralocorticoid action of cortisol. In conclusion, although rare, in cases where conditions such as metabolic alkalosis, resistant hypokalemia, with the absence of classic clinical features of CS, the possibility of ectopic CS should be kept in mind.Table 1.Laboratory results of the patient