Endocrine Abstracts (2008) 15 P170

Atypical thymic carcinoid causing cyclical Cushing's syndrome

VKB Prabhakar1, I Talapatra1, JRE Davis2 & DJ Tymms1

1Department of Endocrinology, Royal Albert Edward Infirmary, Wigan, UK; 2Department of Endocrinology, Manchester Royal Infirmary, Manchester, UK.

A 34-year-old welder presented acutely unwell with a 2-week history of facial puffiness, swollen legs, and weight-gain. His GP had found him to be hypertensive and hypokalaemic and had commenced oral potassium supplements. Clinical examination revealed peripheral oedema (face and legs), BP was 179/100 mmHg, with no Cushingoid features. ECG and CXR were unremarkable. Tests showed leucocytosis but normal CRP, persistent hypokalaemia (2.5 mmol/l), normal venous bicarbonate and glucose. Intravenous potassium replacement was started, followed by oral potassium and Spironolactone. Random serum cortisol was elevated (>1750 nmol/l), with normal renin–aldosterone profile. Further investigations: numerous 24-hour urinary free cortisol levels varied from 28 to >1380 nmol/day (normal <400), 9 am ACTH varied from 71 to 280 ng/l (normal <46), elevated midnight sleeping serum cortisol 438 nmol/l, paradoxical rise in serum cortisol on dexamethasone suppression test and normal pituitary scan. His clinical features resolved spontaneously, with intermittent exacerbations. Inferior petrosal sinus sampling confirmed the lack of a pituitary ACTH gradient but suggested a thoracic lesion. Raised serum ACTH precursor levels suggested an ectopic source and CT imaging revealed a thymus tumour; thymic carcinoid was suspected although urinary 5-HIAA was normal. Following thymectomy, serum cortisol became undetectable. Hydrocortisone replacement was initiated, with good clinical recovery. Histology revealed an atypical carcinoid with local invasive features; he received radical radiotherapy.

Cyclical Cushing’s syndrome (CCS) is a rare clinical disorder, recognized by episodic hypercortisolaemia with intervening periods of normocortisolaemia. Since the ‘cycles’ vary in length, with fluctuating clinical picture and changing biochemistry, diagnosing CCS represents a clinical challenge and requires repeated testing. Further investigations are guided by ACTH-dependency. 26% of CCS is caused by ectopic ACTH production, with thymic tumours accounting for 6 cases so far (Meinardi et al. EJE 2007). We report the seventh patient who had CCS caused by an atypical thymic carcinoid.

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