case_images: PMC6379869_01
case_images: Serum thyroid hormone and TSH levels after the intravenous administration of a single bolus of LT4 (100 mug). Serum FT4 and total T4 levels both increased, peaked 1 hour after the administration, and gradually decreased thereafter.
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case_images: fig1
case_images: Following the intravenous administration of a single bolus of LT4 (100 mug/day), her serum FT4 levels were rapidly and markedly increased in 1 hour (Figure 1).
case_images: Serum thyroid hormone and TSH levels after the intravenous administration of a single bolus of LT4 (300 mug). Serum FT4 (a), FT3 (b), and TSH (c) levels were measured several times of the administration.
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case_images: fig2
case_images: Then, we examined the time course of serum FT4, FT3 and TSH levels for optimization (Figure 2). Serum FT4 and FT3 levels increased within 3 days of the administration and deceased thereafter (Figures 2(a) and 2(b)). Serum TSH levels increased again 14 days after the intravenous administration of a bolus of LT4 (300 mug) in accordance with the decreases observed in serum FT4 and FT3 levels (Figure 2(c)).
case_images: LT4 (300 mug) intravenous administration once in a week and two weeks. A daily oral LT4 (200 mug/day) replacement was continued. PSL (20 mg/day) was also orally administered at the onset of the weekly intravenous administration of LT4 (300 mug). It was tapered to 10 mg/day in a month after the administration. Thereafter, it was tapered by 1 mg/day per a month and subsequently discontinued 10 months after the intravenous administration of LT4. Twelve months after the intravenous administration of LT4, LT4 was intravenously administered once every two weeks, which resulted in the relapse of severe hypothyroidism with elevated serum TSH levels.
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case_images: fig3
case_images: Since then, her serum FT4 and FT3 levels had been maintained as low-normal with the weekly intravenous administration of LT4 for 14 months, whereas serum TSH levels had vary (Figure 3). Thereafter, we carefully tapered the daily doses of PSL by 1 mg per month to avoid steroid withdrawal syndrome and subsequently withdrew PSL administration (Figure 3). Under oral administration of 200 mug/day of LT4, we attempted the intravenous administration of LT4 (300 mug) once in two weeks, which resulted in the relapse of severe hypothyroidism, suggesting the pseudomalabsorption of LT4 due to poor compliance (Figure 3).
case_images: Serum thyroid hormone and TSH levels after the oral administration of a single bolus of LT4 (1400 mug). Eighteen days after the administration, serum FT4 and FT3 levels were 0.83 ng/dL and 1.5 pg/mL, respectively. Her serum TSH levels were 12.78 muIU/mL.
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case_images: fig4
case_images: Following the oral administration of a single bolus of LT4, her serum FT4 levels rapidly elevated within 2 hours (0.52 to 4.56 ng/dL) as shown in Figure 4. Her serum FT4, FT3, and TSH levels were maintained within normal range for 15 days after the single bolus oral administration, and hypothyroidism relapsed thereafter (Figure 4).
case_images: Serum thyroid hormone and TSH levels after the oral administration of a single bolus of LT4 (700 mug). Eight days after the administration, serum FT4 and FT3 levels were 0.82 ng/dL and 1.26 pg/mL, respectively. Her serum TSH levels were 53.1 muIU/mL.
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case_images: fig5
case_images: Under the weekly oral administration of 700 mug of LT4, her serum FT4 and FT3 levels were elevated for 2 hours (FT4: 0.96 to 1.36 ng/dL, FT3: 1.41 to 1.56 pg/mL), and TSH levels decreased (52.8 to 48.6 muIU/mL) without liver dysfunction or electrocardiogram abnormalities (Figure 5). Her serum FT4 and FT3 levels were maintained within normal ranges for 8 days after the single bolus oral administration, which demonstrates the relevance of the weekly oral administration of 700 mug of LT4 (Figure 5).