Dual bronchial carcinoids and Cushing's syndrome with a paradoxical response to dexamethasone and a false positive outcome of inferior petrosal sinus sampling.

Summary, in English

Objective Establishing the cause of Cushing's syndrome can be a considerable challenge, in particular in ectopic ACTH syndrome, and often requires a combination of biochemical tests and imaging procedures. Subject A 27-year-old man presented with signs of Cushing's syndrome. P-ACTH levels were 3 times above the ULN and free urinary cortisol in the order of 1900 nmol/24 h. The work-up showed remarkable results. Results A 2-day low-dose dexamethasone suppression test demonstrated paradoxical increases in cortisol. Sampling from the inferior petrosal sinuses (BIPSS) showed a central to peripheral ACTH ratio of 4.7 after CRH stimulation, i.e. indicated pituitary disease, but MRI of the pituitary was normal and baseline P-CRH <1.0 (ref. <5) pmol/L. CT scan of the lungs showed 2 oval-shaped masses, 1.3 x 1.8 and 1.3 x 2 cm, in the middle lobe. Both were positive at somatostatin receptor scintigraphy, compatible with tumors or inflammatory lesions. Subsequently, 11C-5-hydroxytryptophan-PET showed distinct uptake in the tumors but not elsewhere. Two carcinoids situated 3 cm apart, both staining for ACTH, were removed at surgery. Conclusion This unusual case with dual bronchial carcinoids inducing hypercortisolism illustrates the problems with identifying the source of ACTH in Cushing s syndrome. Possibly, the false positive result at BIPSS reflects an unusual sensitivity of the pituitary corticotrophs to CRH in this patient since ectopic CRH secretion and/or eucortisolism at the time of the procedure could be ruled out. The work-up illustrates the great value of 11C-5-hydroxytryptophan-PET as a diagnostic procedure when other investigations have produced ambiguous results.