Subacute lymphocytic thyroiditis, also known as silent thyroiditis or painless thyroiditis, is a less severe variant of Hashimoto’s thyroiditis and has similar causes and treatment. Unlike Hashimoto's and given its alternative name, it generally presents with a small goiter that is not tender to the touch.
In this form of thyroiditis, the levels of thyroid hormones are usually normal, but on occasion rise to the range of hyperthyroidism, returning to normal, then descending to hypothyroidism. This is due to inconsistent uptake of iodine. These cycles last 2-3 months.
The condition is difficult to diagnose definitively, with a radioactive iodine uptake test being the only conclusive way to confirm the diagnosis.