A 32 year old previously well man of Indian descent presented with headaches and hypertension (BP 190/140). Additional features of metabolic syndrome included newly diagnosed type 2 diabetes mellitus, dyslipidaemia and hepatic steatosis. Low-dose dexamethasone test was abnormal on screening for secondary hypertension, with an elevated ACTH. Despite history of weight gain, clinical signs of cortisol excess were not immediately obvious, with only pale abdominal striae noted. Subsequent shaving of facial hair revealed previously unappreciated rounded facies, acne vulgaris and mild facial hyperpigmentation.
Widened mediastinum on chest x-ray prompted a CT angiography of the chest to exclude aortic dissection. This demonstrated a 63x40mm soft tissue anterior mediastinal mass. Biopsy revealed atypical carcinoid tumour with intense activity on DOTATATE-PET, consistent with a well-differentiated neuroendocrine tumour.
An incidental pituitary microadenoma on CT brain necessitated inferior petrosal sinus sampling, which confirmed an ectopic source of ACTH. Thymectomy was subsequently performed, with post-operative improvement in blood pressure, glycaemic control and lipid profile. 3 month post-operative dexamethasone suppression test had normalised.
Neuroendocrine tumours of the thymus are exceedingly rare, biologically aggressive neoplasms with an estimated incidence of 1 per 5 million people. They account for just 0.4% of all neuroendocrine tumours (1). Although the majority are non-functioning, they are capable of producing a range of biogenic amines predisposing patients to paraneoplastic syndromes (1). There is limited data to guide management. Despite surgical resection and neoadjuvant therapy, >70% develop loco-regional or distant metastases within five years of diagnosis (1), with poor overall five-year survival ranging from 28–68% (1,2,3,4).
The diagnostic challenge in this case was the subtle clinical features of Cushing’s syndrome with an asymptomatic occult primary tumour. Care should be taken to evaluate classical signs of cortisol excess in the context of increased skin pigmentation and obscuring elements such as facial hair.