Differential Diagnosis

The patient presents with high free T4 levels, which suggests hyperthyroidism. The absence of HLA-B27 antigen and normal inflammatory markers (SED, BMP, CRP) along with a negative MRI spine, help to rule out certain autoimmune and inflammatory conditions. Here's a categorized differential diagnosis:

• Single most likely diagnosis
  • Hyperthyroidism (e.g., Graves' disease): Elevated free T4 is a hallmark of hyperthyroidism. The lack of other systemic symptoms or findings does not rule out this condition, as it can present with isolated thyroid function abnormalities.
• Other Likely diagnoses
  • Thyroiditis (subacute or silent): Can cause transient hyperthyroidism due to the release of pre-formed thyroid hormones. The absence of systemic inflammation does not entirely rule out thyroiditis, as some forms can be painless and have minimal systemic symptoms.
  • Exogenous thyroid hormone ingestion: Accidental or intentional ingestion of thyroid hormone can lead to elevated free T4 levels. This diagnosis should be considered, especially if there's access to thyroid medications.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Thyroid storm: Although rare, it's a life-threatening complication of untreated or inadequately treated hyperthyroidism. Early recognition is crucial, even if the patient does not currently exhibit severe symptoms.
  • Pituitary or hypothalamic disorder: Rarely, elevated T4 can be due to a pituitary or hypothalamic problem, such as a TSH-secreting pituitary adenoma. These conditions are less common but critical to diagnose due to their potential impact on health.
• Rare diagnoses
  • Struma ovarii: A rare ovarian tumor that can produce thyroid hormones, leading to hyperthyroidism. This diagnosis would be considered if other causes are ruled out and there are ovarian masses on imaging.
  • Familial dysalbuminemic hyperthyroxinemia: A rare genetic condition that affects the binding of T4 to albumin, leading to elevated free T4 levels without true hyperthyroidism. This condition would be a diagnosis of exclusion and might require specific testing to confirm.