Differential Diagnosis
- Single most likely diagnosis
- Toxic Multinodular Goiter (TMNG): This is the most likely diagnosis given the presence of a multi-nodular goiter, low TSH levels indicating hyperthyroidism, and focal increased activity in the right upper thyroid lobe on uptake scan. The benign biopsy of the thyroid nodule also supports this diagnosis, as TMNG is typically composed of multiple benign nodules.
- Other Likely diagnoses
- Autonomous Thyroid Nodule (ATN): Also known as a "hot" nodule, this condition can cause hyperthyroidism due to a single nodule that is producing thyroid hormone independently of the rest of the thyroid gland. The focal increased activity on the uptake scan and low TSH levels support this diagnosis.
- Thyroiditis (e.g., subacute or silent): Although less likely given the multi-nodular goiter and focal increased activity, thyroiditis can cause hyperthyroidism and a low TSH level. However, the uptake scan would typically show decreased activity in thyroiditis.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Thyroid Cancer (e.g., papillary or follicular): Although the biopsy was benign, it is essential to consider the possibility of cancer, especially if the biopsy was not representative of the entire nodule or if there are other suspicious features. Thyroid cancer can sometimes present with hyperthyroidism, although this is rare.
- Metastatic Disease to the Thyroid: Rarely, metastatic disease (e.g., from breast, lung, or kidney cancer) can involve the thyroid gland and cause hyperthyroidism. This diagnosis would be particularly important to consider in patients with a known history of cancer.
- Rare diagnoses
- Struma Ovarii: A rare ovarian tumor that can produce thyroid hormone, causing hyperthyroidism. This diagnosis would be considered if there were evidence of an ovarian mass and the thyroid uptake scan showed little to no activity.
- TSH-producing Pituitary Adenoma: A rare pituitary tumor that secretes TSH, causing hyperthyroidism. However, this would typically present with elevated TSH levels, not low.
- Hürthle Cell Hyperplasia or Neoplasia: A rare condition characterized by the proliferation of Hürthle cells in the thyroid gland, which can cause hyperthyroidism. This diagnosis might be considered if the biopsy showed Hürthle cell changes.