Endocrine Abstracts

Case history: A 41 year old female was admitted following development of severe hypertension (226/146 mmHg), complicated by heart failure and acute kidney injury. She otherwise had no relevant past medical history. On clinical examination she was obese (BMI 51.94 kg/m²). As part of her cardiac investigations, she underwent a cardiac magnetic resonance imaging (MRI) which detected a 3 cm right sided adrenal nodule. An adrenal biochemical screen identified an elevated plasma normetadrenaline (1418 pmol/l, range<1000) with normal plasma metadrenaline (<180 pmol/l, range <600). This corresponded with high urinary normetadrenaline levels (6998 nmol/24 h, range 0–4900) and normal urinary metadrenaline level (535 nmol/24 h, range 0–2000). Her medications included Doxazosin and Ramipril, which can interfere with the metanephrine assay.

Investigations: A repeat fasting and supine plasma metanephrine sample demonstrated results consistent with previous investigations (plasma normetadrenaline 12 692 pmol/l, metadrenaline <180). The remainder of the adrenal biochemistry screen was reassuring.

Results and treatment: Further characterisation of the suspected adrenal lesion on a dedicated non-enhanced CT adrenals demonstrated bilateral hypodense adrenal lesions measuring 38 mm on the right and 24 mm on the left, consistent with benign adenomas (based on Hounsfield units of <10). Although the imaging was reassuring, rarely phaeochromocytoma can have a density <10 HU ⁽¹⁾. In the light of the abnormal serum and urinary metanephrine results, additional investigations were considered. We were unable to stop antihypertensives that were potentially confounding the assay results due to the severity of her hypertension. Therefore, we employed a molecular imaging approach using [¹¹C] Metomidate PET-CT (MTO-PET) to determine if the adenomas were of adrenocortical origin, therefore excluding a phaeochromocytoma. MTO-PET reassuringly demonstrated tracer uptake by both adenomas. On further questioning, it was noted that the patient was experiencing daytime somnolence, heavy snoring with apnoeic episodes. Following diagnosis and treatment of obstructive sleep apnoea, she achieved normalisation in BP and an improvement in biventricular function on repeat cardiac echocardiogram.

Conclusions: The case highlights the limitations in the specificity of plasma and urinary metanephrine assays, and for the first time highlights the potential role of MTO-PET in excluding a pheochromocytoma by confirming that an adrenal lesion is of adrenocortical origin. This may provide reassurance in cases where there is discordance between biochemistry and radiological findings.

Reference: (1) Management of adrenal incidentalomas: European Society of Endocrinology Clinical Practice Guideline in collaboration with the European Network for the Study of Adrenal Tumors. Eur J Endocrinol 2016. PMID 27390021.