Hashi's attacks the entire thyroid only. It is diagnosed by antibody blood tests...thyroid peroxidase antibody (TPOab) and thyroglobulin antibody (TGab). If either is elevated, Hashi's is indicated. U/S is used to monitor the nodules that so often accompany Hashi's.
A toxic nodule or toxic adenoma is a very different thning. A toxic nodule produces T3 independent of the influence of TSH. So, it's kind of a little rogue thyroid within your thyroid. It doesn't need TSH to stimulate T3 production, so it just keeps cranking out T3. "Nodule" is a very generic term, which can make it hard to research. You might try researching Plummer's disease, which I think will bring you to more pertinent information.
Some people do well on Synthroid (synthetic T4), slow converters have to add a direct source of T3, whether synthetic T3 or dessicated porcine thyroid (Armour, etc.). The debate is long and complicated, but if you search the archives, you will find many discussions on the subject. What works for one may not work for another.
hashimotos is an autoimmune disorder that will continue to progress and hormone levels will have to be increased over time as it eats away at your thyroid. It is diagnosed via ultrasound. It can attack the entire thyroid.
On another note when I finally had blood work for my thyroid this past spring it was all normal. I'm guessing because my left side had compensated. Is it possible for hasimotos to attack part of the thyroid and the entire thyroid?