A 36-year-old woman was found to have a low morning ACTH concentration despite a history of Addison's disease. Past medical history: At the age of 23 years the subject developed Graves's disease, which was treated with radioiodine. At about the same time, she claimed to have two episodes of pancreatitis treated with cholecystectomy. About seven months later she was euthyroid on L-thyroxine (TSH 1.51 mIU/mL) but was admitted with hypotension, hyponatraemia (sodium 109 mmol/L), and low morning cortisol (119 nmol/L). Further investigations confirmed primary adrenal failure with ACTH concentration of 779 pg/mL (ref. range 0-60) prior to the dose of hydrocortisone. About nine years later she complained about tiredness. Clinically she was normotensive and not pigmented. BMI 22.3 kg/m². Periods were regular. ACTH concentration was surprisingly low (ACTH 8.53 pg/mL, ref. range 0-46), despite very low cortisol (3.37 nmol/L). She was admitted for further assessment.
Investigations: Pituitary MRI scan was unremarkable. An insulin tolerance test was performed and showed a clear increase of ACTH (from 15.2 to 165 pg/mL). There was, however, hardly any increase of ACTH after CRH stimulation (from 6.05 pg/mL to 10.2 pg/mL), thus demonstrating central CRH resistance. In summary, this patient developed secondary adrenal failure in the setting of previous Addison's disease. Interestingly, hypoglycaemia (but not CRH) provided a stimulus for ACTH release, thus demonstrating CRH resistance. The case confirms that besides CRH, other factors are responsible for stimulation of the ACTH-cortisol axis during insulin tolerance test.
Keywords: Addison’s disease; adrenal failure; pituitary.