Endocrine Abstracts

Introduction: Localising the aetiology of Cushing’s syndrome can be challenging, especially when investigations utilised are limited in their sensitivities and specificities. We present a case whereby the reliabilities of laboratory and radiological investigations are tested to their limits.

Case Presentation: A 70 year old female presented with a one year history of fatigue, weight gain and headaches. She had proximal myopathy, cheek telangiectasia and abdominal striae, suspicious for Cushing’s syndrome. Past medical history includes hypothyroidism, hypercholestrolaemia, hypertension and depression. Two sets of 24hour urinary cortisol excretion screened positive with elevated cortisol levels on overnight dexamethasone suppression testing. On high dose dexamethasone suppression, her cortisol levels suppressed to less than 50 nmol/l, suggesting a pituitary ACTH-dependent aetiology. However, her MRI pituitary and inferior petrosal sinus samplings were unremarkable. CT thorax, abdomen and pelvis were also unremarkable. Thus, a MRI Ga68 DOTANAC scan was performed, initially revealing no somatostatin receptor positive lesions. Her thoracic MRI singled out a 1.2 cm left lower lobe nodule. Additionally, her whole body MIBG Iodine123 was unremarkable. A whole body FDG PET CT followed, revealing a 1.2 cm×1.1 cm nodule within the left lower lobe demonstrating low activity. On a re-review of her DOTANAC scan, a small focus of trace activity was noted at a 7mm nodule in the left lung base with mild somatostatin receptor positivity corresponding to the thoracic MRI. She was referred for a video assisted thoracoscopy with left lower lobectomy. Histology revealed an 11mm cream-coloured nodule, classified as a typical ACTH-producing carcinoid tumour.

Conclusion: Limitations in investigations for Cushing’s syndrome should always be taken into account when requesting tests. Small carcinoid tumours producing ACTH can elude a variety of imaging modalities and it is therefore essential consider specialist imaging such as NM Ga68 DOTANAC upon discussion with radiologists, especially when considering ectopic sources.