**7.3. Differential diagnosis**

If a patient presented with diffuse goiter with clinical and biochemical thyrotoxicosis, ophthalmopathy and positive autoimmune markers like anti TPO antibody or TSHR-Ab, diagnosis of Graves' disease is straight forward. In absence of these classical features radionuclide scan (I123, I131, Tc99m) in the most reliable distinguishing test. In case of Graves' disease there is diffuse and high uptake, whereas in patients with toxic adenoma or toxic multinodular goiter there is patchy uptake. In patients with thyroiditis and factitious thyrotoxicosis there is decreased uptake. In patients with TSH producing adenoma, there is also a diffuse goiter, but TSH is inappropriately normal or increased instead of suppress TSH of graves' disease. Panic attacks, mania, pheochromocytoma and malignancy can be easily ruled out by thyroid function test.
