Introduction: TSH secreting pituitary adenomas (TSHomas) are often large and locally invasive. Following trans-sphenoidal surgery (TSS) patients frequently require adjuvant treatment with either anti-thyroid medication or somatostatin analogue therapy.
Objective: To evaluate the value of a single subcutaneous octreotide test dose in predicting the the response to long term treatment in 5 patients with TSHomas.
Methods: Five consecutive patients presenting 2000-02 were evaluated (4 before TSS, one post-TSS). All five subjects (2 male, 36-76 years) had elevated free T4 (mean 44.4 pmol/L, range 31.5 - 57.8, ULN: 26.0) and total T3 levels (mean 4.2 nmol/L, range 2.9 - 5.8, ULN 2.6) with inappropriately normal or elevated TSH (mean 5.82mU/L, range 1.50 - 16.49, ULN 5.50). Each subject underwent an octreotide test dose (50mcg); serum TSH and alpha subunit levels were determined at baseline and hourly for six hours. Subjects were subsequently treated (four as primary therapy, one post-TSS) with long term subcut octreotide (1 patient), or depot lanreotide (4 patients), with evaluation at 3 months. Three out of four patients given primary treatment with somatostatin analogues went on to TSS.
Results: Serum TSH fell progressively by 52% (range 46-61%) from baseline levels by 6 hours. No significant fall in alpha subunit levels was observed. 3 month follow-up data is available on four following long term treatment with octreotide or lanreotide: three patients had normalisation of thyroid function, and one patient demonstrated a 41% drop in fT4 (50.6 to 29.7 pmol/L).
Conclusion: Our data demonstrate that a 46-61% drop in TSH after 50mcg octreotide test dose is consistent with a therapeutic response to long term therapy in terms of normalisation of fT4. However, further studies will be needed to demonstrate what degree of initial TSH fall is required to predict long term responsiveness.