Final answer:
The patient is likely to have postpartum thyroiditis, indicated by the painless thyroid mass, elevated T4, and low RAIU. Treatment would be supportive, possibly including beta-blockers for hyperthyroid symptoms, and thyroid hormone replacement if hypothyroidism ensues.
Step-by-step explanation:
The 26 year-old female who is presenting with a painless thyroid mass, an enlarged thyroid seen upon physical exam, elevated T4 and low radioactive iodine uptake (RAIU) is likely to be diagnosed with postpartum thyroiditis. This diagnosis is suggested by her clinical presentation and the laboratory findings indicating hyperthyroidism, which occurs when the thyroid gland is overactive, producing excess thyroid hormones. Postpartum thyroiditis typically happens within the first year after childbirth and can present in the hyperthyroid phase, as seen with this patient's elevated T4.
The treatment of choice for this patient would initially be supportive, addressing the symptoms, as the condition often resolves on its own within a few months. In some cases, beta-blockers may be prescribed to manage symptoms such as palpitations or tremors. Should the condition progress to the hypothyroid phase, which can happen after the hyperthyroid phase, thyroid hormone replacement therapy may be necessary. It is important to monitor the thyroid function tests regularly during this period.