A 43-year-old woman, visits the internal medicine outpatient clinic complaining of easy fatigue, weight loss and intolerance to cold weather. On examination she has thyroid swelling and dry skin. Ultrasonography shows diffuse symmetric thyroid gland enlargement. She has low T3 and T4 as well as elevated anti-TPO and anti-TG serum levels. 

What is the most likely diagnosis of this case?