Preliminary observations using endocrine markers of pituitary venous dilution during bilateral simultaneous inferior petrosal sinus catheterization in Cushing's syndrome: is combined CRF and TRH stimulation of value?

OBJECTIVE: We determined whether the measurement of hormones in pituitary blood permits correction for dilution by non-pituitary blood during bilateral simultaneous inferior petrosal sinus blood sampling in Cushing's syndrome.

DESIGN: Bilateral simultaneous inferior petrosal sinus blood sampling was performed after combined hCRF and TRH stimulation. Peak ACTH concentrations were corrected for the TSH and PRL inter-sinus ratio, assuming uniform secretion of both hormones into each inferior petrosal sinus.

PATIENTS: Eight patients with clinical and biochemical features of Cushing's syndrome.

MEASUREMENTS: Basal and stimulated ACTH, TSH and PRL concentrations were measured after bilateral simultaneous inferior petrosal sinus blood sampling and simultaneously from a peripheral forearm vein.

RESULTS: Basal central:peripheral ACTH ratio misdiagnosed four of eight patients as having non-pituitary disease. Peak uncorrected ACTH central:peripheral ratio erroneously suggested two of eight patients had non-pituitary disease. ACTH central:peripheral ratio corrected by TSH and PRL correctly predicted pituitary-dependent disease in all eight cases and provided correct lateralization data in four of five patients with a unilateral pituitary microadenoma.

CONCLUSION: This study suggests that measuring other hormones in pituitary blood after TRH stimulation can offer a simple and reliable method for correcting for dilution by non-pituitary blood during bilateral simultaneous inferior petrosal sinus blood sampling in Cushing's syndrome.