Differentiating between Cushing's disease of pituitary origin and ectopic ACTH syndrome of extra-pituitary origin remains a major challenge to the clinician because of limitations in the diagnostic accuracy of the high-dose dexamethasone suppression test. Routine use of inferior petrosal sinus sampling (IPSS) is therefore advocated by some authors for these patients. We present our preliminary experience of IPSS in 7 consecutive patients with Cushing's disease and discuss how the results impacted on the patients' management.
The dexamethasone suppression test is a useful endocrinological test to diagnose Cushing's syndrome. However, its interpretation may be influenced by many factors such as stress, alcohol, failure to ingest the dexamethasone, altered metabolism, drug interaction and obesity. This report illustrates such an instance, whereby the result of the test was erratic due to the anti-tuberculous drug rifampicin. Rifampicin has been found to profoundly attenuate the biological effects of dexamethasone, probably by enhancing its metabolism in the liver. The exact mechanism of the drug interaction remains elusive, though induction of hepatic CYP3A4 enzyme complex is a possible mechanism. In a patient treated with rifampicin, the results of dexamethasone suppression tests thus have no diagnostic value and can be very misleading.
Between January 1978 to December 1993, 130 cases of adrenal diseases were diagnosed and surgically treated at the National University of Malaysia. They were 58 cases (44.6%) of Conn's syndrome, 40 cases (30.7%) of Cushing's syndrome, 20 cases (15.3%) of phaeochromocytoma and 12 cases (9.2%) of adrenocortical carcinoma (ACC). The commonest cause of Conn's syndrome was an adenoma (96.5%) which affected the left gland four times more than the right gland. Cushing's syndrome was caused by adrenocortical adenoma (32.5%), diffuse bilateral adrenal hyperplasia (40.0%), pigmented macronodular hyperplasia (20.0%) and adrenal carcinoma (7.5%). Twenty-five percent of the phaeochromocytomas were extraadrenal in origin arising mainly from the abdominal sympathetic chain. More than 50% of ACCs were non-functioning tumours. Fifty percent of the patients with ACC had inoperable tumours. The prognosis was poor even with adjuvant chemoradiotherapy. The main surgical approach was the anterior transabdominal route. There was no operative mortality or morbidity in all operated cases.
Ocular hypertension caused by endogenous Cushing syndrome from an ectopic adrenocorticotropic hormone-producing tumor is rare. We report an 11-year-old boy who presented with intraocular pressures (IOPs) of 50 mm Hg in both eyes. Surgical resection of the tumor was performed with subsequent normalization of serum cortisol and IOP levels.