Long-term outcomes of tissue-based ACTH-antibody assay-guided transsphenoidal resection of pituitary adenomas in Cushing disease

OBJECTIVE Cushing disease is caused by a pituitary micro- or macroadenoma that hypersecretes adrenocorticotropic hormone (ACTH), resulting in hypercortisolemia. For decades, transsphenoidal resection (TSR) has been an efficacious treatment but with certain limitations, namely precise tumor localization and complete excision. The authors evaluated the novel use of a double-antibody sandwich assay for the real-time quantitation of ACTH in resected pituitary specimens with the goals of augmenting pathological diagnosis and ultimately improving long-term patient outcome. METHODS This study involved a retrospective review of records and an analysis of assay values, pathology slides, and MRI studies of patients with Cushing disease who had undergone TSR in the period from 2009 to 2014 and had at least 1 year of follow-up in coordination with an endocrinologist. In the operating room, biopsy specimens from the patients had been analyzed for tissue ACTH concentration. Additional samples were simultaneously sent for frozen-section pathological analysis. The ACTH assay performance was compared against pathology assessments of surgical tumor samples using receiver operating characteristic (ROC) analysis and against pre- and postoperative MRI studies. RESULTS Fourteen patients underwent TSR with guidance by ACTH-antibody assay and pathological assessment of 127 biopsy samples and were followed up for an average of 3 years. The ACTH threshold for discriminating adenomatous from normal tissue was 290,000 pg/mg of tissue, based on jointly maximized sensitivity (95.0%) and specificity (71.3%). Lateralization discordance between preoperative MRI studies and surgical visualization was noted in 3 patients, confirming the impression that MRI alone may not achieve optimal localization. A majority of the patients (85.7%) attained long-term disease remission based on urinary free cortisol levels, plasma cortisol levels, and long-term corticosteroid therapy. Comparisons of patient-months of remission and treatment failure showed that the remission rate in the study sample statistically exceeds the rate in historical controls (71.9%; p = 0.0007, Fisher's exact test). Long-term unexpected hormonal deficiencies were statistically similar between study patients (29%) and those in a meta-analysis (25%; p = 0.7596, Fisher's exact test). CONCLUSIONS These preliminary findings reflect the promising potential of tissue-based ACTH-antibody-guided assay for improving the cure rates of Cushing disease patients undergoing TSR. Further studies with larger sample sizes, further refinements of assay interpretation, and longer-term follow-ups are needed.

Rapid intraoperative immunoassay of parathyroid hormone and other hormones: a new paradigm for point-of-care testing

BACKGROUND

The first description of the use of a rapid assay for the measurement of intact parathyroid hormone (PTH) in patients undergoing parathyroidectomy for hyperparathyroidism was reported in 1988. Subsequent improvements in the analytical performance of the rapid intraoperative PTH assay allowed the establishment of its clinical utility in the surgical management of hyperparathyroidism. These modifications also allowed the assay to be performed in or near the operating suite.

METHODS

We searched MEDLINE, using the following key words: intraoperative, rapid, quick, parathyroid hormone, hormone, and immunoassay. Relevant articles that focused on the analytical aspects and clinical utility of rapid intraoperative hormone immunoassays were selected for this review.

CONTENT

On the basis of the positive impact that the rapid intraoperative PTH test has had on both patient outcomes and cost savings, other rapid intraoperative hormone immunoassays for the diagnosis and/or treatment of other endocrine-hormone-secreting tumors have been developed. These hormones share certain characteristics that make them suitable for use as rapid intraoperative tests, i.e., short analyte half-life and/or large analyte concentration gradient, rapid analysis time, and positive clinical utility. Initial studies with cortisol, gastrin, insulin, adrenocorticotropic hormone, and testosterone have shown promising results in preoperative localization studies and/or for assessing the effectiveness of tumor resection during surgery.

CONCLUSION

The emergence of these rapid intraoperative immunoassays indicates that this test format is likely to provide future opportunities to improve patient care by advances in clinical laboratory testing.

Direct intraoperative micromethod for hormone measurements of pituitary tissue in Cushing's disease

BACKGROUND

During transsphenoidal surgery (TSS) for Cushing's disease, the surgeon depends on experience to find minute adenomas. Cytological slide preparations or frozen sections, even when successful, are not specific concerning the hormone activity. In an attempt to improve accurate localization of minute ACTH adenomas, we evaluated a new intraoperative method of ACTH measurements in adenoma and anterior lobe microsamples. As most ACTH adenomas are monohormonal, the possible benefit of a GH measurement was investigated.

METHODS

We included pituitary tissue of 32 patients, 22 with Cushing's disease and 10 endocrine inactive pituitary adenomas as control. All patients underwent TSS by one surgeon. Preoperative data, intraoperative and perioperative hormone measurements of homogenized, weighed pituitary tissue samples, and histological findings are presented.

RESULTS

In ACTH adenomas, the median ACTH content was found to be 1,688 ng/mg, minimum 345 ng/mg. The median GH was measured at 36 ng/mg. Anterior lobe tissue contained median 80 ng ACTH/mg, maximum 279 ng/mg. Median GH was 2,200 ng/mg. In hormonally inactive adenomas ACTH was less than 0.1 ng/mg, median GH was 5.5 ng/mg. There was no overlap of ACTH content in the tissues investigated. Therefore, by adopting 300 ng ACTH/mg as a cutoff level, a clear discrimination is given. Additional GH measurements are not necessary.

CONCLUSION

This new intraoperative method permits a clear differentiation between adenoma and pituitary tissue. In addition to intraoperative cytology and histology, this method can serve as a specific proof that the ACTH adenoma has been identified during surgery. This may be valuable in difficult cases with unclear intraoperative findings, especially after previously negative exploration.

Intraoperative adrenocorticotropin levels during transsphenoidal surgery for Cushing's disease do not predict cure

Recently, intraoperative rapid immunochemiluminometric assay (ICMA) ACTH measurements have been used to evaluate the completeness of resection of ectopic ACTH-secreting tumors. This study evaluates whether this method can be applied to patients undergoing transsphenoidal surgery (TSS) for Cushing's disease to predict complete pituitary tumor resection. Eighteen patients with Cushing's disease undergoing TSS had plasma ACTH concentrations measured by a standard ICMA every 10 min for 1 h immediately after pituitary tumor removal. Patients were evaluated postoperatively for cure by standard criteria. ACTH levels were evaluated for percentage decrease from baseline at each time point. Patients who were cured (n = 11) had statistically greater decreases in ACTH levels (mean decrease 54%) than patients who were not (n = 7; 26% mean decrease, P < 0.04). By Receiver-Operator Characteristic (ROC) analysis, a reduction of at least 40% best predicted which patients were cured and which were not cured. This level of reduction was observed in 82% of cured patients, and a reduction of less than 40% was observed in 71% of those not cured. The analysis misclassified 4 of the 18 patients, resulting in a diagnostic accuracy of 78%. Although the mean maximal decrease in ACTH concentrations after tumor removal was significantly different between cured and not cured patients with Cushing's disease, it was less dramatic than results in the previous ectopic ACTH study. This may relate to incomplete suppression and/or surgical manipulation of normal pituitary corticotrophs in patients with pituitary disease. In summary, in contrast to the ectopic ACTH syndrome, decline of plasma ACTH during TSS does not accurately predict complete tumor resection.