A 34-year-old primigravida at 14 weeks of gestation presents with fatigue, weight gain, cold intolerance, and constipation. Thyroid function tests show TSH 8.6 mIU/L with low-normal free T4. Thyroid peroxidase antibodies are markedly elevated at 980 IU/mL. High-resolution ultrasound of the thyroid is performed. The structure marked **A** in the diagram shows a diffusely hypoechoic and heterogeneous parenchyma compared to the strap muscles. Based on this sonographic finding and the clinical presentation, what is the most likely diagnosis?
A. Iodine deficiency goitre with compensatory hyperplasia
B. Thyroid lymphoma with diffuse infiltration
C. Hashimoto thyroiditis with subclinical hypothyroidism in pregnancy
D. Graves disease with thyroid eye disease
Explanation
Why Hashimoto thyroiditis with subclinical hypothyroidism in pregnancy is right
The diffusely hypoechoic and heterogeneous parenchyma (marked A) is the pathognomonic ultrasound finding of Hashimoto thyroiditis. Combined with markedly elevated thyroid peroxidase antibodies (980 IU/mL), elevated TSH (8.6 mIU/L), low-normal free T4, and clinical symptoms of hypothyroidism (fatigue, cold intolerance, weight gain, constipation, puffy face, slow reflexes), this constellation defines Hashimoto thyroiditis with subclinical hypothyroidism in pregnancy. The ATA Guidelines on Management of Thyroid Disease in Pregnancy 2017 emphasize that this sonographic appearance—diffuse heterogeneity with loss of normal echogenicity—is highly specific for autoimmune thyroiditis and warrants antibody testing and TSH-suppressive levothyroxine therapy in pregnancy to protect fetal neurodevelopment.
Why each distractor is wrong
Graves disease with thyroid eye disease: Graves disease presents with hyperthyroidism (elevated free T4, suppressed TSH), not subclinical hypothyroidism. Ultrasound shows diffuse hypoechogenicity but with increased vascularity and a different clinical picture (heat intolerance, tachycardia, weight loss). Thyroid eye disease is absent in this patient.
Thyroid lymphoma with diffuse infiltration: While lymphoma can present with diffuse hypoechogenicity, it typically presents with rapid growth, hard texture, and constitutional symptoms. Markedly elevated TPO antibodies and positive anti-thyroglobulin antibodies are not typical of lymphoma; lymphoma would show monoclonal B-cell infiltration, not autoimmune markers.
Iodine deficiency goitre with compensatory hyperplasia: Iodine deficiency causes diffuse enlargement but typically shows a more uniform, less heterogeneous echotexture. TSH would be elevated with normal or elevated free T4 (compensatory), not low-normal free T4. Thyroid antibodies would be negative, not markedly elevated.
High-YieldNEET PG
Diffusely hypoechoic heterogeneous parenchyma on thyroid ultrasound + elevated TPO antibodies + elevated TSH = Hashimoto thyroiditis; in pregnancy, treat to TSH target <2.5 mIU/L to protect fetal neurodevelopment.
ATA Guidelines on Management of Thyroid Disease in Pregnancy 2017
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