Questions on brain tumors and thyroid stuff

Q. In the nervous system lecture, under the “tumors of the brain” section, I am confused on if they are benign or malignant. Gliomas are malignant? While the rest are benign?

A. We don’t really use the terms benign and malignant a lot when talking about brain tumors. For one thing, brain tumors don’t metastasize (which as you know is one measure of malignancy). For another thing, they ALL can cause serious problems (even death) if they’re in the wrong spot – even if they are small. In general, though, we consider most brain tumors, with the exception of meningioma, to be malignant. Meningiomas have a good prognosis – they grow in a non-injurious way (they sort of push the normal tissue to the side rather than invading), and they are generally in places where they can be resected easily – so they are generally called benign.

Q. For Graves disease, I do not understand how ANTI-TSH receptor antibodies stimulate thyroid growth.

A. Yeah it’s weird. There are anti-TSH-receptor antibodies in both Hashimoto and Graves disease, and they work in opposite ways: in Hashimoto disease, they block the receptor, and in Graves disease, they stimulate the receptor. I don’t know the molecular mechanisms of how that works (and that’s probably not what you’re asking anyway) – but for some reason, the antibodies have opposite effects. They must bind to different epitopes on the receptor or something. For some reason, the antibodies in Graves must act enough like TSH that the receptor thinks its being stimulated – and the antibodies in Hashimoto probably just block the receptor so TSH can’t bind.

Q. For the non-neoplastic diseases, are only some associated with hyper or hypothyroidism? As in they all are some abnormality of the thyroid, and one of the symptoms of the abnormal thyroid can be hypothyroidism (Riedel Thyroiditis, Hashimoto) or hyperthyroidism (Grave’s)?

A. Some non-neoplastic diseases present with hypothyroidism, some present with hyperthyroidism, and some present with neither (they just show up as an enlarged thyroid). To make matters worse, some diseases can present with hyperthyroidism and then progress to hypothyroidism (DeQuervain thyroiditis, for example, can have hyperthyroidism early on, as the follicles are busted open and the colloid leaks out – and then hypothyroidism later as the disease heals). Goiters are usually hypothyroid – but they can also be hyper or euthyroid.

I think the ones you really need to remember hypo/hyper for are Hashimoto disease (most common cause of hypothyroidism in the US) and Graves disease (most common cause of hyperthyroidism in the US). The others are not so clear-cut, and it’s probably not worth trying to memorize what the thyroid hormone levels are at presentation and as the disease progresses. I doubt anyone will ask you about that.

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