J Med Cases

Journal of Medical Cases, ISSN 1923-4155 print, 1923-4163 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Med Cases and Elmer Press Inc

Journal website https://jmc.elmerpub.com

Case Report

Volume 17, Number 7, July 2026, pages 365-370

Transient Supplement-Associated Thyrotoxicosis Without Persistent Hyperthyroidism: A Diagnostic Challenge in Endocrine Practice

↓ Figure 1. (a) Ultrasound examination of the thyroid gland with data on normal shape, size, localization, and ultrasound structure of the parenchyma. (b) Color Doppler with data on normal blood supply.

↓ Figure 2. Thyroid scintigraphy using 99m technetium pertechnetate (thyroid scan) approximately 30 days after the initial biochemical diagnosis. Normal uptake of the marker was seen in both lobes of the thyroid gland.

↓ **Table 1.** Basic Investigations of Thyroid Function Tests Demonstrating Thyrotoxicosis (Suppressed TSH, Elevated FT4 and FT3)
Lab test	Value	Reference range
Anti-TgAb: anti-thyroglobulin antibody; Anti-TPO-Ab: anti-thyroperoxidase antibody; CRP: C-reactive protein; FT3: free triiodothyronine; FT4: free thyroxine; Tg: thyroglobulin; TRAb: TSH receptor antibody; TSH: thyroid-stimulating hormone.
Hemoglobin	132	120–160 g/L
CRP	4.1	0–10 mg/L
Fasting glucose	5.31	2.8–6.1 mmol/L
Serum potassium	4.6	3.5–5.6 mmol/L
Serum sodium	139.7	136–151 mmol/L
Serum chlorine	101.2	96–110 mmol/L
Urea	4.8	2.6–7.2 mmol/L
Creatinine	78.5	44–96 µmol/L
TSH	0.005↓	0.34–5.6 mU/L
FT4	36.85↑	7.86–14.41 pmol/L
FT3	14.13↑	3.8–6.0 pmol/L
Anti-TgAb	2.53	0–4 IU/mL
Anti-TPO-Ab	0.26	0–9 IU/mL
TRAb	0.806	0–1.5 IU/L
Tg	67.4	3.5–77 ng/mL

↓ Table 1. Basic Investigations of Thyroid Function Tests Demonstrating Thyrotoxicosis (Suppressed TSH, Elevated FT4 and FT3)

Lab test

Value

Reference range

Anti-TgAb: anti-thyroglobulin antibody; Anti-TPO-Ab: anti-thyroperoxidase antibody; CRP: C-reactive protein; FT3: free triiodothyronine; FT4: free thyroxine; Tg: thyroglobulin; TRAb: TSH receptor antibody; TSH: thyroid-stimulating hormone.

Hemoglobin

132

120–160 g/L

CRP

4.1

0–10 mg/L

Fasting glucose

5.31

2.8–6.1 mmol/L

Serum potassium

4.6

3.5–5.6 mmol/L

Serum sodium

139.7

136–151 mmol/L

Serum chlorine

101.2

96–110 mmol/L

Urea

4.8

2.6–7.2 mmol/L

Creatinine

78.5

44–96 µmol/L

TSH

0.005↓

0.34–5.6 mU/L

FT4

36.85↑

7.86–14.41 pmol/L

FT3

14.13↑

3.8–6.0 pmol/L

Anti-TgAb

2.53

0–4 IU/mL

Anti-TPO-Ab

0.26

0–9 IU/mL

TRAb

0.806

0–1.5 IU/L

67.4

3.5–77 ng/mL

↓ **Table 2.** Hormone Results Over Follow-Up Showing Transient Subclinical Hypothyroidism Observed and the Following Normalization of Thyroid Function
Lab test	First	After 60 days	After 90 days	Reference range
FT3: free triiodothyronine; FT4: free thyroxine; TSH: thyroid-stimulating hormone.
TSH	0.005 ↓	9.689	4.468	0.34–5.6 mU/L
FT4	36.85 ↑	9.48	11.78	7.86–14.41 pmol/L
FT3	14.13 ↑	3.89	4.58	3.8–6.0 pmol/L

↓ Table 2. Hormone Results Over Follow-Up Showing Transient Subclinical Hypothyroidism Observed and the Following Normalization of Thyroid Function

Lab test

First

After 60 days

After 90 days

Reference range

FT3: free triiodothyronine; FT4: free thyroxine; TSH: thyroid-stimulating hormone.

TSH

0.005 ↓

9.689

4.468

0.34–5.6 mU/L

FT4

36.85 ↑

9.48

11.78

7.86–14.41 pmol/L

FT3

14.13 ↑

3.89

4.58

3.8–6.0 pmol/L

↓ **Table 3.** Timeline of Clinical Presentation, Investigations, Management, and Follow-Up
Time from symptom onset	Clinical event
FT3: free triiodothyronine; FT4: free thyroxine; TSH: thyroid-stimulating hormone.
Approximately 2 months before presentation	Initiation of menopausal dietary supplement
Day 0	Onset of palpitations and cardiology evaluation; sinus tachycardia documented
Days 1–3	Thyroid function tests demonstrated thyrotoxicosis (suppressed TSH, elevated FT4 and FT3)
Shortly after diagnosis	Endocrinology consultation and discontinuation of dietary supplement
Initial endocrine evaluation	Normal thyroid ultrasonography and Doppler examination; negative thyroid autoantibodies
Approximately day 30	Thyroid scintigraphy with technetium-99m pertechnetate showed normal uptake
Approximately day 60	Transient subclinical hypothyroidism observed during follow-up
Approximately day 90	Normalization of thyroid function tests and clinical recovery

↓ Table 3. Timeline of Clinical Presentation, Investigations, Management, and Follow-Up

Time from symptom onset

Clinical event

FT3: free triiodothyronine; FT4: free thyroxine; TSH: thyroid-stimulating hormone.

Approximately 2 months before presentation

Initiation of menopausal dietary supplement

Day 0

Onset of palpitations and cardiology evaluation; sinus tachycardia documented

Days 1–3

Thyroid function tests demonstrated thyrotoxicosis (suppressed TSH, elevated FT4 and FT3)

Shortly after diagnosis

Endocrinology consultation and discontinuation of dietary supplement

Initial endocrine evaluation

Normal thyroid ultrasonography and Doppler examination; negative thyroid autoantibodies

Approximately day 30

Thyroid scintigraphy with technetium-99m pertechnetate showed normal uptake

Approximately day 60

Transient subclinical hypothyroidism observed during follow-up

Approximately day 90

Normalization of thyroid function tests and clinical recovery