Which symptom is most likely associated with a diagnosis of thyroiditis related to a viral infection?

Reduced uptake on thyroid isotope scan is indeed the most characteristic finding associated with thyroiditis due to viral infections. In cases of thyroiditis, inflammation of the thyroid gland can impair its ability to absorb iodine, leading to reduced radioiodine uptake during an imaging study. This is particularly evident in subacute thyroiditis, which may follow a viral infection, such as those caused by mumps or influenza.

The inflammation associated with viral infections can disrupt normal thyroid function, leading to transient hypothyroidism or hyperthyroidism, but regardless of functional status, the reduced uptake appears consistently on the scans. This provides a diagnostic clue to differentiate it from other thyroid conditions, such as Graves' disease, where increased uptake is typically observed, usually alongside different clinical symptoms.

In the context of the other options: bilateral exophthalmos is more commonly associated with Graves' disease or thyroid eye disease rather than viral thyroiditis. A diffuse, smooth goiter can be seen in hypothyroid conditions but does not specifically indicate viral infection-related thyroiditis. While positive thyroid peroxidase antibodies indicate autoimmune thyroiditis (such as Hashimoto's), they are not specific to viral infections. Thus, the reduced uptake on thyroid scans stands out as the most relevant and indicative symptom in this