GHRP-2 administration significantly increased TSH levels in 40% of patients with TSH-producing pituitary adenomas, suggesting diagnostic utility.
Background
Thyrotropin (TSH)-producing adenomas are a rare and challenging type of functional pituitary adenoma that causes hyperthyroidism. The diagnosis is often difficult, requiring complex endocrine evaluations to differentiate it from other causes of thyrotoxicosis. Current diagnostic methods, like the TSH-releasing hormone (TRH) test, can yield ambiguous results; in this study, a poor response was observed in most patients. Since growth hormone-releasing peptide-2 (GHRP-2) does not normally induce TSH secretion in healthy individuals, researchers hypothesized that an abnormal response to GHRP-2 could serve as a specific biomarker for these tumors. This study explores GHRP-2's potential to unmask the paradoxical TSH secretory dynamics of these adenomas, offering a new diagnostic angle.
Study Design
This clinical study evaluated 5 patients (4 women, 1 man) with suspected TSH-producing adenomas. The researchers examined TSH secretory dynamics by administering a series of challenge tests. Each patient underwent a GHRP-2 test, a TSH-releasing hormone (TRH) test, an octreotide suppression test, and a bromocriptine suppression test. The primary endpoint for the GHRP-2 test was a significant response, defined as a serum TSH level increase of >50% above the baseline measurement. The study also assessed the TSH response post-operatively in one patient who had their adenoma completely removed to see if the abnormal response was corrected.
Results
The GHRP-2 test triggered a significant TSH response in 2 of 5 patients (40%), with serum TSH levels rising by more than 50% from baseline. An additional patient showed a near-significant 48% increase in TSH. In contrast, the standard TRH test was less effective, with 4 of 5 patients (80%) showing a poor TSH response. The octreotide suppression test significantly decreased serum TSH levels in 2 of 5 patients (40%). No patients demonstrated a significant response to the bromocriptine test.
In one patient whose adenoma was completely removed, post-operative testing showed that the basal serum TSH was suppressed and, critically, the TSH level failed to increase in response to GHRP-2 administration, confirming the adenoma was the source of the paradoxical response.
This highlights the potential specificity of the GHRP-2 test for active TSH-producing adenomas.
Key Findings
- 2 of 5 patients (40%) with TSH-producing adenomas had a >50% increase in serum TSH after a GHRP-2 test.
- 1 additional patient showed a 48% increase in serum TSH in response to GHRP-2.
- 4 of 5 patients (80%) demonstrated a poor response to the standard TRH test.
- 2 of 5 patients (40%) had significant TSH suppression following octreotide administration.
- Following complete tumor removal in 1 patient, the TSH response to GHRP-2 was abolished.
Why It Matters
This research suggests that the GHRP-2 stimulation test could be a valuable addition to the diagnostic toolkit for TSH-producing pituitary adenomas, especially when traditional tests like the TRH test are inconclusive. For clinicians, a paradoxical TSH increase after GHRP-2 administration could be a strong indicator of this rare tumor type. While not universally responsive (40% of patients), it provides another layer of evidence to guide diagnosis and treatment. The key takeaway is that GHRP-2, normally associated with GH release, can have off-target diagnostic value in specific pituitary pathologies. This is still an early-stage finding based on a very small patient cohort, so it is far from being a standard clinical protocol. Further validation in larger patient groups is necessary before it can be widely adopted for differential diagnosis of hyperthyroidism.
