It is relatively rare but Reidel's thyroiditis can be painful. It is important to see an endocrinologist who has experience in thyroid ultrasound to help make this diagnosis. Biopsy is sometimes helpful. More likely, this is a painful variant Hashimoto's thyroiditis.
from what i've just read on the web, reidel's thyroiditis is extremely rare [like only 3 cases in the 1800s]. my recommendation is that you go to a doctor or endocrinologist and get tested.
[from Mescape Reference] Some experts feel that RT is not primarily a thyroid disease but rather that it is a manifestation of the systemic disorder multifocal fibrosclerosis. Approximately one third of RT cases are associated with clinical findings of multifocal fibrosclerosis at the time of diagnosis. (See Etiology.)
In 1883, Professor Bernhard Riedel first recognized the disease. He published a description of 2 cases in 1896 and of a third case in 1897.[1] Riedel used the term eisenharte struma to describe the stone-hard consistency of the thyroid gland and its fixation to adjacent structures. He noted the presence of chronic inflammation with fibrosis and the absence of malignancy on microscopic examination. Simple wedge resection of the thyroid isthmus was used to alleviate tracheal obstruction and is still the preferred surgical therapy for RT.
blessings to you.
good luck.