Abstract
Background: Thymic carcinoids are rare neoplasms that account for less than 5% of all thymic tumors. Approximately 25% of these tumors will result in Cushing’s syndrome due to ectopic ACTH secretion. These tumors can also be associated with MEN1 syndrome. This is a case report of a patient with history of macroprolactinoma now presenting with Cushing’s syndrome due to ectopic ACTH production from a thymic carcinoid tumor.
Clinical Case: This is a 57 year old male with history of pituitary macroprolactinoma diagnosed in 2011, now status post transsphenoidal resection and external beam radiation therapy, with persistent hyperprolactinemia on cabergoline, who presented to our clinic for a routine follow up visit. Patient had already developed secondary hypogonadism and secondary hypothyroidism as a consequence of treatment for the macroprolactinoma. He complained of worsening fatigue and weight gain ongoing for several months. Laboratory studies revealed an hemoglobin A1c of 8.3% (nl < 5.7%), TSH 0.24 MIU/L (0.4-4.5 MIU/L), free T4 1.2 ng/dL (0.8-1.8 ng/dL), 8 AM cortisol 31.4 mcg/dL (4-22 mcg/dL), ACTH 185 pg/mL (6-50 pg/dL), prolactin 29.6 ng/mL (2-18 ng/mL), IGF-1 88 ng/mL (50-317 ng/mL). Follow up labs confirmed cushings syndrome: cortisol AM-DST 36.4 mcg/dL (< 2 mcg/dL), free urinary cortisol 291.9 mcg/24h (2-50 mcg/24h). Pituitary MRI showed empty sella turcica. Cortisol after an 8 mg DST 32.5 mcg/dL (< 5 mcg/dL). CT chest, abdomen and pelvis revealed an heterogeneously enhancing solid anterior mediastinal mass measuring 4.9 x 3.1 x 4.3 cm. Whole body OctreoScan showed a markedly hyperintense large mass adjacent to the right heart border measuring 47 x 32 mm. He was referred to cardiothoracic surgery and underwent a right video-assisted thoracic surgery with resection of the anterior mediastinal mass. Pathology revealed a thymic well-differentiated neuroendocrine tumor with strong cytoplasmic staining for ACTH. It was also positive for OSCAR, Cam5.2, synaptophysin, CD56, and S100. Ki67 stain was positive in fewer than 1% of tumor cells. Final diagnosis was carcinoid tumor.
Conclusion: Cushing’s syndrome secondary to ectopic ACTH secretion from a thymic carcinoid is rare. The presence of two MEN1-associated tumors in this patient, macroprolactinoma and thymic carcinoid, is highly suggestive of a clinical diagnosis of MEN 1.
Massive Thymic Hyperplasia Mimicking Anterior Mediastinal Neoplasia in Occult Graves' Disease
