We present a case of a middle-aged lady with clinical features suspicious of Addisons, however an initial false negative short synacthen test (SST), resulted in delay of diagnosis.
Case: A 62-year-old lady presented to ED with a month history of generalised malaise, weakness, dizziness and vomiting. She had a background of type2 diabetes mellitus, previous left parathyroidectomy for primary hyperparathyroidism and B-thalassaemia trait. Admission bloods included Na 129 mmol/l, K 5.6 mmol/l. She had raised infection markers. She received 200 mg intravenous hydrocortisone in ED followed by broad spectrum antibiotics. Chest XR showed small left pleural effusion, not amenable to pleural tap or drainage. Initial SST performed approximately 15 h post hydrocortisone dose, showed good response (Table 1).
A few days later, in view of high clinical suspicion, the SST was repeated showing a flat response (Table 1), suggestive of hypoadrenalism. CT chest showed a loculated left-sided pleural effusion, as well as bulky adrenal glands suggestive of adrenal hyperplasia. Adrenal antibodies, remaining pituitary screen, autoimmune and viral screens were negative. TB was excluded. Following her diagnosis of Addisons, she was initiated on hydrocortisone and her clinical symptoms have significantly improved.
|Cortisol (nmol/l)||Initial SST||2nd SST|
|Renin (nmol/l per hour)||9|
Discussion: The initial false negative SST in our patient may be due to the hydrocortisone dose received, although this was 15 h prior. The biological half-life of hydrocortisone is 100 mins, however this may be increased in context of stress, acute illness, certain diseases, and concomitant drugs (e.g. hepatic microsomal inhibitors of cytochrome P-450). Whilst the SST remains the standard screening test for hypoadrenalism, this case demonstrates the importance of ensuring results are interpreted in context of the clinical suspicion. Where clinical suspicion remains high, the test should be repeated, ideally in a non-acute setting to prevent delay of diagnosis.