These sonographic, clinical and available laboratory findings are suggestive of either subacute lymphocytic thyroiditis or Graves disease.

Thyroiditis is more common in young age, while Graves is more common in middle-aged females. Also, in thyroiditis the thyroid is usually of average size and shows heterogenous parenchyma, while in Graves it's typically markedly enlarged with rather homogenous parenchyma.

In this case, the common findings between thyroidits and Graves are the thyrotoxicosis and the increased vascularity of the thyroid.

For the above mentioned reasons, subacute lymphocytic thyroiditis is favored over Graves disease in this case. However, further laboratory investigation, searching for anti-TSH receptor antibodies, would be recommended to reach a final diagnosis. This test would be positive in Graves and negative in subacute lymphocytic thyroiditis.