Endocrine Abstracts

Background: Hypercortisol states present a diagnostic conundrum. Other conditions such as cyclical and subclinical Cushings pose additional challenges. We report a complex clinical presentation of thymoma with coexisting subclinical Cushing’s.

Case report: A 65-year-old man presented to chest clinic with breathlessness and anterior mediastinal mass on CXR. CT scan demonstrated a 7.5 cm probable thymoma and bilateral adrenal masses of varying sizes up to 5.3 cm. Patient has well controlled hypertension on four antihypertensive. No other features of hypercortisolism.

24 h urinary free cortisol were normal on three occasions as were 24 h urinary metanephrines and 5HIAA. MRI of adrenals showed atypical appearance for adenomas. PET scan demonstrated positive uptake in anterior mediastinal mass and adrenal glands raising suspicion of hormonal correlation between mediastinal and adrenal masses despite initial normal Endocrine results. CT guided biopsy of mediastinal mass confirmed thymoma.

Repeated hormonal assessment showed non suppressible cortisol after overnight dexamethasone and subsequent LDDST and HDDST also resulted in a failure of cortisol suppression with cortisol (nmol/l) 425 and 497 respectively. ACTH was undetectable (<5 ng/l). Patient underwent thymectomy with perioperative steroid cover.

Repeated interval adrenal MRI remained unchanged. Repeat LDDST and HDDST cortisone non-suppression (403 and 350 nmol/l) respectively. ACTH was <5 ng/l. Iodo cholesterol scan demonstrated ACTH independent macronodular adrenal hyperplasia. Then patient will be treated medically for subclinical Cushing’s with interval scans.

Conclusion: Bilateral macronodular hyperplasia is a rare cause and it accounts for 1% of adrenal Cushing’s. Patient with subclinical Cushing’s may have normal urinary free cortisol level. But there is a failure of cortisol supression by low dose dexamethasone.