Dissociation between TSH and prolactin dynamics in treated thyrotoxicosis

TSH and prolactin secretory patterns in thyroid disease have generally been reported as concordant. We studied TSH and prolactin responses to TRH infusion (500 mug) in euthyroid individuals previously treated for thyrotoxicosis with 131I or antithyroid drugs. The 131I-treated group (seven men, twenty women) had been clinically and biochemically euthyroid (normal serum thyroxine and triiodothyronine levels) for 6 months to 4-5 years (kappa +/- SD = 17-1 +/- 4-1 months). Based on maximal TSH increment (deltaTSH), three patient groups were identified: Group 1 [normal deltaTSH, n = 6]: delta prolactin was normal in two, blunted in one and exaggerated in three. Group 2 (exaggerated TSH response, n = 8): delta prolactin was normal in two, blunted in one and exaggerated in five. Group 3 (TSH nonresponders, n = 13): delta prolactin was normal in five, blunted in three, and exaggerated in five. Eleven patients (three men, eight women) were studied after 6 months antithyroid-drug treatment. All were clinically and biochemically euthyroid. All but one showed a blunted TRH-TSH response. All three men showed an exaggerated delta prolactin as did four of eight women. Three women showed a blunted delta prolactin and in one, delta prolactin was normal. Thus, TRH-induced TSH and prolactin response patterns in treated thyrotoxicosis are not uniformly concordant, and, while a blunted or absent TSH response commonly persists long after euthyroidism has been restored, this is most frequently accompanied by a normal or exaggerated prolactin response.