We report four female patients with nodular goiter (in two of the four due to Hashimoto's thyroidits) and one male patient with frank hypothyroidism due to Hashimoto's thyroiditis in whom TSH-suppressive or replacement L-T-4 therapy failed to suppress or, respectively, normalize serum TSH. As is typical in our country, our patients took L-T-4 15-20 min before a light breakfast, Gastrointestinal or other diseases and drugs known to interfere with the intestinal absorption of L-T-4 were not the cause of this failure, The gastrointestinal absorption test of L-T-4 (1000 mu g) was performed in four patients; in three patients it revealed peculiar abnormalities in that (i) the absorption peak was >70% but occurred at 4 hr vs an average of 2 hr in 12 euthyroid controls (EC) and 3 hr in 10 primary hypothyroid controls (HC); (ii) 50% of the maximal absorption occurred at 110 min vs 45 min in EC and 50 min in HC; (iii) the maximal increment in T-4 absorption was between 90 and 120 min (+111%) vs between 30 and 60 min in EC (+312%) and HC (+354%), In sum, only the first part of the absorption curve of T-4 was shifted to the right (in three of the four women) and this shift was more pronounced and extended to the second part of the curve in the fourth patient; in this last patient absorption peak was 44% at 180 min, Based on these results, we obtained full suppression or normalization of TSH by postponing breakfast for at least 60 min after T-4 ingestion. The precise cause for the ''inertia'' in the early phase of T-4 absorption is not known, but since it was observed in two patients with euthyroid nodular goiter, it is not associated with hypothyroidism per se.
