Introduction: Primary adrenal insufficiency (Addison's disease) is characterized by low cortisol and high levels of adrenocorticotropic hormone (ACTH). In patients with Addison's disease, ACTH levels are often higher than 250 pg/mL. However extreme level of ACTH despite steroid replacement prompt further evaluation and we outline an interesting case here.
Case description: 20 y/o male patient with obesity (BMI 37.8) and vitiligo was referred to the adrenal center with the diagnosis of Addison disease and marked elevation of ACTH, >2000 pg/mL despite being on high doses of steroid replacement consisting of prednisone 10 mg daily. ACTH had been rising and a year ago ACTH was 425 pg/ml. Patient was first diagnosed with Addison and 17 years of age presenting at that time with 50 pounds of weight loss and fatigue and was started on prednisone. Patient endorses good compliance with medication within 7AM to 11AM. Denies any weight loss, low BP, nausea, fatigue, abdominal pain, muscle cramps or weakness, salt craving or hyperpigmentation. Pituitary function was otherwise normal as evidenced by a normal testosterone and prolactin level, He did have subclinical hypothyroidism with a TSH of 5.69 µU/mL and normal FT3 (4.2 pg/mL). Further testing was performed for the cause of the ACTH elevations since he did not have any symptoms of adrenal insufficiency. We switched the patient to hydrocortisone 25 mg in the morning and 10 mg in the evening. A dexamethasone suppression test to evaluate the etiology of ACTH secretion is pending and both chest X ray and pituitary MRI scan are pending.
Discussion: The high ACTH could be related to at least three different mechanisms. Issues can be with the pituitary, adrenals, or ectopic secretion. Differential includes lab assay interferences such as due to heterophilic antibodies or dietary supplement use which can result in falsely elevated ACTH. We have already excluded these causes. ACTH excess could also be due to anterior pituitary tumors or ectopic ACTH secreting tumors. For additional testing we changed prednisone to hydrocortisone for monitoring purpose due to its short half-life. We also ordered chest X-ray and pituitary MRI to evaluate ectopic and pituitary causes of excess ACTH production. Patient will follow up in few months with the results. This interesting case does not have a definite diagnosis yet. However, physicians should be aware of extreme elevation of ACTH and that should prompt additional imaging and work up to evaluate possible causes.
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