Patients with this disorder usually have an acute phase of thyroiditis in which the gland may be painful and anti-thyroid antibodies may be present. At this time, patients are thyrotoxic, with an elevated serum T4 and decreased radioiodine uptake.
Progressive euthyroid and hypothyroid periods of 4-8 weeks may follow before thyroid functions finally normalize. Subacute thyroiditis shows a rapidly enlarging thyroid gland and signs of thyroid dysfunction. It has an acute course and is often associated with pain and tenderness in the area of the gland. It is also accompanied by an elevated erythrocyte sedimentation rate. It can cause "low-uptake" toxicosis, in that they can produce elevated serum levels of thyroid hormones in the face of low to normal levels of radioactive iodine uptake.