Differential Diagnosis for Low TSH and Elevated T4 and T3

Single Most Likely Diagnosis

• Hyperthyroidism due to Graves' Disease: This condition is characterized by an autoimmune stimulation of the thyroid gland, leading to excessive production of thyroid hormones (T4 and T3), which in turn suppresses TSH production. The low TSH level (0.04) along with elevated T4 (1.55) and T3 (3) is consistent with this diagnosis.

Other Likely Diagnoses

• Toxic Multinodular Goiter: This condition involves the growth of multiple nodules in the thyroid gland that produce thyroid hormones independently of TSH, leading to hyperthyroidism. The laboratory values provided could be consistent with this diagnosis, especially if the patient has a palpable goiter or if ultrasound findings support this condition.
• Thyroiditis: Inflammation of the thyroid gland can cause the release of stored thyroid hormones into the bloodstream, leading to transient hyperthyroidism. However, this condition might not fully explain the sustained elevation of T3 and T4 without other supporting evidence of thyroiditis.
• Exogenous Thyroid Hormone Ingestion: Intentional or accidental ingestion of thyroid hormone medication can suppress TSH production and elevate T4 and T3 levels. A thorough patient history is necessary to consider this diagnosis.

Do Not Miss Diagnoses

• Thyroid Storm: Although rare, thyroid storm is a life-threatening complication of untreated or inadequately treated hyperthyroidism. It presents with severe symptoms of hyperthyroidism and can be fatal if not promptly recognized and treated. The laboratory values alone do not diagnose thyroid storm, but the clinical presentation is critical.
• Pituitary Tumor (TSH-producing Adenoma): A rare tumor of the pituitary gland that secretes TSH, leading to hyperthyroidism. This diagnosis would typically require additional testing, including MRI of the pituitary and possibly other hormone level assessments.

Rare Diagnoses

• Struma Ovarii: A rare ovarian tumor that contains thyroid tissue, which can produce thyroid hormones, leading to hyperthyroidism. Diagnosis would require imaging and possibly surgical exploration.
• Familial Dysalbuminemic Hyperthyroxinemia: A rare genetic condition affecting the binding of T4 to albumin, leading to elevated levels of free T4 and potentially low TSH, despite euthyroidism. Specific tests to evaluate thyroid hormone binding proteins would be necessary for diagnosis.
• Resistance to Thyroid Hormone: A rare genetic disorder where the body's tissues are resistant to thyroid hormone, leading to elevated T4 and T3 levels with a nonsuppressed TSH. However, the very low TSH in this case makes this diagnosis less likely.