Differential Diagnosis for Elevated Thyroid Peroxidase with Normal T3 and T4 in a Patient Complaining of Dry Eyes

• Single Most Likely Diagnosis
  • Hashimoto's thyroiditis: This is the most likely diagnosis given the elevated thyroid peroxidase (TPO) antibodies, which are a hallmark of autoimmune thyroiditis. The presence of dry eyes could be related to the autoimmune nature of the disease, possibly indicating an association with Sjögren's syndrome, which is sometimes seen in conjunction with Hashimoto's. Normal T3 and T4 levels suggest that the thyroid function is currently euthyroid, but the patient is at risk of developing hypothyroidism over time.
• Other Likely Diagnoses
  • Subclinical thyroiditis: This condition can present with elevated TPO antibodies and normal thyroid hormone levels. It may be a transient condition, but it can also be a precursor to permanent hypothyroidism. Dry eyes could be a symptom of the underlying autoimmune process.
  • Sjögren's syndrome: Although primarily known for causing dry eyes and dry mouth, Sjögren's can be associated with various autoimmune conditions, including thyroiditis. The elevated TPO antibodies could indicate a co-existing thyroid condition.
• Do Not Miss Diagnoses
  • Graves' disease: Although less likely given the normal T3 and T4 levels, Graves' disease can sometimes present with elevated TPO antibodies and euthyroid or even hypothyroid function, especially in the early stages or during the transition from hyperthyroidism to hypothyroidism. It's crucial not to miss this diagnosis due to its potential for significant morbidity if left untreated.
  • Thyroid lymphoma: A rare condition, but one that could present with elevated TPO antibodies and normal thyroid function tests. Dry eyes could be part of a broader symptom complex. This diagnosis is critical to identify due to its severe prognosis if not promptly treated.
• Rare Diagnoses
  • Painful thyroiditis (subacute thyroiditis): This condition can present with elevated TPO antibodies, although it's more commonly associated with a painful thyroid gland. The normal T3 and T4 levels might not be typical, as subacute thyroiditis often goes through phases of hyperthyroidism and hypothyroidism. Dry eyes could be part of a systemic inflammatory response.
  • Silent thyroiditis: A form of thyroiditis that can present with transient hyperthyroidism or hypothyroidism but might have normal thyroid function tests at the time of evaluation. Elevated TPO antibodies could be present, and dry eyes might be related to an autoimmune component.