Which of the following statements is true about hyperthyroidism?

The correct statement regarding hyperthyroidism is that T3 thyrotoxicosis is an exception. In hyperthyroidism, especially in conditions like Graves' disease, it is common to see elevated levels of both T3 (triiodothyronine) and T4 (thyroxine). However, in T3 thyrotoxicosis, patients may present with normal or low levels of T4 along with elevated T3. This situation can lead to symptoms of hyperthyroidism without the typical high levels of T4, making it an exception within the broader context of hyperthyroid states.

Understanding T3 thyrotoxicosis helps clarify the range of presentations in hyperthyroid patients, underscoring the need for comprehensive evaluation beyond just the usual T4 elevations. In contrast, elevated TSH levels would actually suggest hypothyroidism (or a pituitary issue) rather than hyperthyroidism, which is characterized by low TSH. Low free T4 levels contradict the definition of hyperthyroidism, and Graves' disease is well-established as an autoimmune disorder, primarily due to the presence of thyroid-stimulating immunoglobulins acting against the thyroid.