Autoimmune primary adrenal insufficiency masked by chronic steroid inhaler use
James Allanson, Aditi Sharma, Tannaz Vakilgilani, St Mary’s Hospital, Imperial College Healthcare NHS Trust
A 17-year-old Irish girl presented with severe hyponatraemia following a 5-day history of unexplained vomiting and abdominal pain associated with dizziness and weakness. She was complaining of chronic fatigue and recurrent dizzy spells for the past few years. She was known asthmatic on regular steroid inhaler since the age of 6. She did not take her steroid for few days prior to her admission. There was no family history of note. Her BMI was 17kg/m2 despite a good appetite and her examination was unremarkable apart from hyperpigmentation on her lower limbs.
Her initial investigations showed Na+ 119 mmol/L, K+ 4.9mmol/L urea 8.5 mmol/L and eosinophils 0.4*10x9 /L. She had a compensated metabolic acidosis despite vomiting. She was noted to be constantly hypotensive despite adequate fluid replacement. Her sodium normalised to 135 mmol/L within 24 hours with fluid resuscitation alone. Paired plasma osmolality was 260 mOsm/kg with urine osmolality of 630mOsm/kg suggestive of borderline hypotonic hyponatraemia.
The possibility of adrenal insufficiency raised on the ground of clinical and biochemical picture. Subsequent short synacthen test showed cortisol at 0, 30 and 60 minutes as follows: 88, 100 and 99nmol/L respectively. She also had a raised ACTH level of 964ng/L and positive adrenal antibodies which confirmed primary adrenal failure. Remaining autoimmune screen, TFTs, immunoglobulins, coeliac screen, gastric parietal antibodies, TB monospot test and serum ACE were all normal. High urinary Na+ of 191 mmol/L with low urinary K+ combined with a very low aldosterone level and a markedly raised plasma renin were suggestive of mineralocorticoid deficiency. Her adrenal MRI showed bilateral small adrenal glands.
She was started on hydrocortisone replacement at a dose of 10mg, 5mg, and 5mg and fludrocortisone 100mcg once daily which resulted in rapid improvement in her symptoms.
This illustrates an interesting clinical case of underlying autoimmune primary adrenal insufficiency masked by exogenous steroid inhaler use for concurrent treatment of asthma. She was mildly symptomatic for adrenal insufficiency for years prior to admission. Should patients on low dose exogenous steroid with similar symptoms and signs have a work up to rule out underlying adrenal insufficiency?