Endocrine Abstracts

Case history: A 74-year-old gentleman with primary aldosteronism (PA) was referred for the ‘MATCH’ study – a prospective comparison of 11C-metomidate PET CT with adrenal vein sampling. He took no exogenous steroids.

Investigations: Na 147 mmol/l, K 3.7 mmol/l, aldosterone 496 pmol/l, renin activity <0.17 nmol/l per h, random cortisol 247 nmol/l and concomitant ACTH 9.3 ng/l. Two overnight dexamethasone suppression tests recorded values of 61 and 24 nmol/l (<50). CT showed a 1.5 cm nodule on the left and a smaller nodule on the right. Adrenal vein sampling (table) showed apparent non-cannulation of the right adrenal vein. Metomidate-PET CT scan demonstrated high left adrenal adenoma uptake, with a diagnostic ratio L:R of 2.43 (<1.25).

Right

Left

IVC

Aldosterone (pmol/l)

2,256

59,100

5,650

Cortisol (nmol/l)

1,836

4,552

1,739

Aldosterone/cortisol ratio

1.2

12.9

3.2

Selectivity index (>3)

1.0

2.6

Lateralisation index

1

10.6

Results and treatment: Following left adrenalectomy, he was discharged on amlodipine 10 mg and hydrocortisone 10 mg. Histopathology confirmed a 9×9 mm adrenal ‘nodularity’ with a mixture of cells resembling either zona glomerulosa (ZG) or zona fasciculata (ZF). Eight weeks later, he reported severe tiredness. The 0900 cortisol was 69 nmol/l, ACTH 4 ng/l. His short synACTHen values were 41, 207 and 271 nmol/l. His symptoms resolved on steroid replacement. CT of his pituitary was normal. Post-operative blood pressure is 136/68 mmHg, renin 1.3 nmol/l per h and aldosterone 80 pmol/l.

Conclusions and points for discussion: Sustained post-operative adrenal insufficiency is, unusually, associated with isolated ACTH insufficiency. His small adenoma, with mixed ZG- and ZF-like cells, does not fit the picture of contralateral adrenal suppression by a large ZF-like adrenal adenoma co-secreting cortisol and aldosterone. A positive PET CT in MATCH permits adrenalectomy despite apparent failure of adrenal vein cannulation; in thee of nine patients to date, we have observed post-operative adrenal suppression. Suppressed cortisol production in the contralateral gland, from autonomous production by the adenoma, could result in a diminished selectivity index and misinterpreted as failure to cannulate the right adrenal vein. Under-expression of CYP11B1 (11 β-hydroxylase), due to variants in its gene promoter, is a common feature of PA (MacKenzie et al 2017). We postulate that adrenal insufficiency is an under-recognised consequence of removing half of the adrenal mass; and that administering dexamethasone at induction of general anaesthesia may convert sub-clinical to overt insufficiency by suppressing the pituitary at the critical moment of adaptation to adrenalectomy.