Differential Diagnosis for TSH <0.10 and T4 1.92 in a 2 Month Postpartum 32 Year Old Female

• Single Most Likely Diagnosis
  • Postpartum Thyrotoxicosis: This condition is a common cause of thyrotoxicosis in the postpartum period, often resulting from the exacerbation of underlying autoimmune thyroid disease (e.g., Graves' disease) or the development of postpartum thyroiditis. The low TSH and elevated T4 levels are consistent with this diagnosis.
• Other Likely Diagnoses
  • Graves' Disease: An autoimmune disease that causes hyperthyroidism, characterized by low TSH and high T4 levels. It can be exacerbated during the postpartum period.
  • Postpartum Thyroiditis (Hyperthyroid Phase): Although typically presents with a destructive thyroiditis pattern (low T4 and low TSH), some cases can have elevated T4 levels during the initial phase due to the release of pre-formed thyroid hormones.
• Do Not Miss Diagnoses
  • Thyroid Storm: A life-threatening complication of untreated or inadequately treated hyperthyroidism. Although the patient's T4 level is not extremely high, any symptoms suggestive of thyroid storm (e.g., fever, tachycardia, agitation) warrant immediate attention.
  • Pituitary Adenoma (TSH-Producing Adenoma is less likely given the low TSH, but a non-functioning adenoma could potentially cause secondary hyperthyroidism due to TSH suppression): Although rare, a pituitary adenoma could potentially cause alterations in thyroid function tests, including low TSH and elevated T4, especially if there is secondary involvement of the thyroid axis.
• Rare Diagnoses
  • Struma Ovarii: A rare ovarian tumor that can produce thyroid hormones, leading to hyperthyroidism. It would be an unusual cause of postpartum thyrotoxicosis but should be considered in the differential diagnosis of hyperthyroidism with unclear etiology.
  • Familial Dysalbuminemic Hyperthyroxinemia: A rare condition characterized by an abnormal albumin that binds T4 with high affinity, leading to elevated T4 levels but normal free T4 and TSH levels. However, the low TSH in this case makes this diagnosis less likely.
  • Other rare causes of hyperthyroidism, such as metastatic thyroid cancer or exogenous thyroid hormone ingestion, should also be considered but are less likely in the postpartum context without additional suggestive history or findings.