A 44 year old lady has just recovered from an upper respiratory tract infection. What is the SINGLE most likely diagnosis related to her symptoms and lab results?

The context of the question suggests that the patient is a 44-year-old woman who has recently recovered from an upper respiratory tract infection, which is a significant clue in substantiating the diagnosis of subacute thyroiditis.

Subacute thyroiditis is often preceded by viral infections, particularly upper respiratory infections. This condition typically presents with a painful enlargement of the thyroid gland and can be associated with fever, malaise, and an elevated erythrocyte sedimentation rate (ESR), indicating inflammation. In the post-viral phase, symptoms can include transient hyperthyroidism followed by hypothyroidism as the inflammation damages thyroid cells and subsequently may lead to a reduction in hormone production.

In contrast to other conditions like Hashimoto's thyroiditis, which is an autoimmune disorder and develops more insidiously, or Graves' disease, characterized by excessive hormone production and often accompanied by eye symptoms, subacute thyroiditis has a specific viral origin and is marked by its association with a recent viral illness. Toxic nodular goitre usually involves autonomous nodules that produce excess thyroid hormone independently of TSH regulation and is less likely to have a direct relationship to a recent upper respiratory infection.

Given these contextual nuances, the symptoms and likely laboratory findings aligning with a recent viral