Differential Diagnosis for High T3 and T4 with Suppressed TSH and Negative Thyroid Antibodies
- Single Most Likely Diagnosis
- Toxic Multinodular Goiter (TMNG): This condition is characterized by the presence of multiple nodules in the thyroid gland that produce excess thyroid hormones, leading to hyperthyroidism. The high levels of T3 and T4, suppressed TSH, and the absence of thyroid antibodies support this diagnosis. The nodular thyroid mentioned in the question further points towards TMNG.
- Other Likely Diagnoses
- Toxic Adenoma: A solitary thyroid nodule that produces thyroid hormones autonomously, causing hyperthyroidism. While less likely than TMNG given the description of a nodular thyroid, it remains a possibility, especially if one nodule is significantly more active than others.
- Thyroiditis (Subacute or Silent): Although thyroiditis typically presents with positive thyroid antibodies, there can be cases, especially in the early phase of silent thyroiditis, where antibodies are not yet detectable. The absence of antibodies does not completely rule out this condition, but it makes it less likely.
- Do Not Miss Diagnoses
- Thyroid Cancer with Functional Metastases: Although rare, metastatic thyroid cancer can produce thyroid hormones, leading to hyperthyroidism. The presence of a nodular thyroid and hyperthyroidism necessitates consideration of this potentially life-threatening condition.
- Struma Ovarii: A rare ovarian tumor that contains thyroid tissue, which can produce thyroid hormones and cause hyperthyroidism. This condition is crucial to consider due to its potential impact on fertility and the need for surgical intervention.
- Rare Diagnoses
- Familial Non-Autoimmune Hyperthyroidism: A rare genetic condition leading to hyperthyroidism without the presence of thyroid antibodies. This diagnosis would be considered if there's a family history of similar conditions.
- HCG-Induced Hyperthyroidism: In rare cases, high levels of human chorionic gonadotropin (hCG), such as in pregnancy or choriocarcinoma, can stimulate the thyroid gland to produce excess thyroid hormones. This would be considered in the context of pregnancy or suspected trophoblastic disease.
- Iatrogenic Hyperthyroidism: Exogenous thyroid hormone ingestion, either intentionally or unintentionally, can lead to suppressed TSH and elevated T3 and T4 levels without thyroid antibodies. This diagnosis should be considered, especially if there's a history suggestive of thyroid hormone supplementation or factitious disorder.