Inferior petrosal sinus sampling in the diagnostic evaluation of Cushing's syndrome: K.E.M. experience

An overlap in the clinical and biochemical features of the more common pituitary Cushing's disease and the rare ectopic ACTH secreting tumors often leads to a diagnostic dilemma. High quality computed imaging modalities have a poor sensitivity and do not always help in localising the tumor. Inferior petrosal sinus sampling (IPSS) with measurement of ACTH levels localizes the source of excess ACTH secretion and aids in the differential diagnosis of ACTH dependant Cushing's syndrome.

To analyze the efficacy of inferior petrosal sinus sampling in the basal state and its role in the diagnostic evaluation in patients of Cushing's syndrome.

Forty four patients of proven Cushing's syndrome underwent HDDS and pituitary imaging followed by IPSS (unstimulated). The data was analysed in 39 patients with definite histopathological diagnosis which included 34 patients with Cushing's disease, four with ectopic Cushing's syndrome and one with adrenal carcinoma. A centre:periphery ratio of plasma ACTH levels of > or =2 was considered diagnostic of Cushing's disease.

Cannulation rate was 100%. No neurological complications were encountered. IPSS could correctly localize the lesion in 23 of 34 patients of Cushing's disease (sensitivity: 67.6%). All patients of ectopic Cushing's syndrome and adrenal carcinoma had a ratio of <2 (specificity: 100%). IPSS helped in localization of the lesion and improved the diagnostic yield from 26.7% to 73.5%.

IPSS helps in localization in patients of Cushing's syndrome with a diagnostic dilemma and should be carried out only in centers with suitable expertise.