23 year-old female patient from Belo Horizonte seeks medical attention complaining of hypersomnia and fatigue for the past 5 months. Physical examination reveals painless, normal-size thyroid, slightly bigger consistency, with 3 palpable thyroid nodes in both lobes, smaller then 0,5cm each. Laboratorial review shows serum TSH concentration of 10,68mcIU/mL (Ref.: 0,55-4,78), free T4 concentration of 0,87ng/dL (Ref.: 0,8-1,9) and serum antithyroid peroxidase antibody (TPO) concentration over 1300UI/mL (Ref.: <60UI/mL). No other abnormalities were found. Ultrasound was requested, as shown.


Thyroid ultrasound in axial plane showing (A) both lobes and (B) the left lobe.

Doppler thyroid ultrasound in (A and C) sagittal and (B) axial plane focused on the left lobe.

Question:
After analyzing the images and according to clinical data, which one is the most likely diagnosis and its cause?

(Medical Residence 2017- Universidade Federal de Sergipe - Q82) It's a form of hypothyroidism in general population, caused by a complex immunologic phenomenon, resulting in lymphocytes infiltration and consequent fibrosis, in the presence of TSH blockers antibodies and decreasing number and efficiency of follicles. Those are characteristics of: