Endocrine Crisis and Obstruction: ACTH-producing Small Cell Lung Cancer Presenting With Superior Vena Cava Syndrome

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Abstract Introduction: Small cell lung cancer (SCLC) accounts for about 15% of all lung cancers. The most common paraneoplastic syndromes include: SIADH (15-40%), ectopic ACTH syndrome (2-5%), and Lambert Eaton Myasthenic syndrome (3%). Superior vena cava (SVC) syndrome, on the other hand, occurs more commonly in non-small cell lung cancer (NSCLC) compared to SCLC, however in 10% of SCLC cases, SVC syndrome is seen on presentation. Case: A 64-year-old female, former 20-pack year smoker, with no past medical history, presented with newly diagnosed hypertension (200/110 mm Hg) and hypokalemia (K+ 2.7 mmol/L) after years without medical care. She was started on hydrochlorothiazide-losartan and potassium supplementation. Two weeks later, she presented to the emergency department with dyspnea, elevated blood pressure (185/119 mm Hg), tachycardia (99 bpm). Initial investigations revealed potassium 2.4 mmol/L, bicarbonate 33 mmol/L, and troponins 37. Physical examination revealed facial plethora, tachycardia, and clear lung fields, with a chest X-ray consistent with a right paratracheal mass. Transthoracic echocardiography (TTE) unveiled a moderate pericardial effusion suggestive of impending tamponade, prompting urgent pericardiocentesis. Subsequent CT chest without contrast exposed a large right paratracheal mediastinal mass and a spiculated lung lesion with a small pericardial effusion. Given persistent hypokalemia, metabolic alkalosis, and a cushingoid appearance, suspicion arose for ectopic adrenocorticotropic hormone (ACTH) secretion from SCLC, confirmed by elevated ACTH and serum cortisol levels. Spironolactone was initiated for hypertension and refractory hypokalemia management. Patient had persistent dyspnea, recurrent pericardial effusion, requiring a pericardial window. Biopsy of the mass conformed SCLC. After the pericardial drain removal, she had distended neck veins, worsening facial plethora, and right arm swelling. CT chest with contrast revealed a large mediastinal mass compressing and invading SVC pointing towards SVC syndrome. The patient began chemotherapy with cisplatin and etoposide, followed by immunotherapy with durvalumab, and radiation therapy with significant improvement. Discussion: This is a case of SCLC, with ectopic adrenocorticotropic hormone (ACTH) secretion, complicated by malignant pericardial effusion, and concurrent superior vena cava syndrome on presentation. Given the initial chest CT was without contrast, and patient's facial plethora was attributed to her Cushing's syndrome, SVC syndrome was not entertained on presentation. However, the patient's persistent facial plethora and development of right upper arm swelling, ameliorated by positional changes suggested a concomitant Superior Vena Cava (SVC) syndrome. This case highlights the importance of considering SVC syndrome in the differential diagnosis of a patient who presents with SCLC.

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