Poster Presentation ESA-SRB 2023 in conjunction with ENSA
Distinguishing subclinical Cushing’s disease from a nonfunctioning pituitary tumour – unreliability of the intravenous dexamethasone suppression test (#343)
Background:
Subclinical Cushing’s disease (SCD) is not a well-known entity with diagnostic challenges. This is the first report with a normal 4mg IVDST in SCD.
Clinical Case:
A 43-year-old woman was seen in the Endocrine clinic for evaluation of pituitary macroadenoma. She did not have symptoms and signs of Cushing’s syndrome, acromegaly, panhypopituitarism.
Her baseline pituitary profile (table1) revealed a mildly elevated IGF-1. Subsequent oral glucose tolerance test excluded acromegaly with a nadir GH of 0.1 mg/L. MRI of pituitary fossa revealed a right-sided cystic pituitary lesion (Figure1) and the pituitary gland was expanded, encroaching on the suprasellar cistern but did not impinge on the optic chiasm. She was planned for trans-sphenoidal resection after a MDT meeting.
A preoperative hormonal profile was similar to baseline (table1). Given the high normal ACTH of 44ng/L, she underwent a 24-hour urine free cortisol and 1mg overnight DST (Table2). With the non-suppressed DST and mildly elevated urine free cortisol, a 4mg IVDST was done. It showed normal suppression of serum cortisol to <130 nmol/L on day2 (Table 3). This was interpreted as ruling out Cushing’s disease according to the criteria established by Jung et al. (1).
Postoperatively, her morning cortisol continued to fall (+4h:1150nmol/L -> Day1:775nmol/L -> Day2:167nmol/L -> Day3:69nmol/L). She reported a worsening headache on day3, with no clinical signs of adrenal insufficiency. A diagnosis of glucocorticoid withdrawal syndrome was made (2). She was commenced on replacement hydrocortisone. Immunohistochemistry showed a corticotroph tumour with positivity for T-Pit and ACTH (Figure 3 and 4).
Conclusion:
- Suspect SCD with pituitary adenoma if there is high normal ACTH despite a normal cortisol level and absence of Cushingoid features.
- SCD diagnosis is confirmed if peripheral CRH stimulation and/or IPSS is in keeping with a pituitary source and subsequent tissue immunohistochemistry confirms T-Pit and ACTH staining.
- Jung C, Alford FP, Topliss DJ, Burgess JR, Long F, Gome JJ, et al. The 4-mg intravenous dexamethasone suppression test in the diagnosis of Cushing's syndrome. Clinical Endocrinology. 2009; doi:10.1111/j.1365-2265.2009.03756.x
- Theiler-Schwetz V, Prete A. Glucocorticoid withdrawal syndrome: What to expect and how to manage. Curr Opin Endocrinol Diabetes Obes. 2023; 30(3):167–74. doi:10.1097/med.0000000000000804