The outer part of my eyebrow is thinning out badly. I heard this was related to thyroid but I checked and it was normal. What else could cause it?

Test thyroid further. A "normal" thyroid test is very common in those who are hypothyroid! Most docs just screen with a TSH and think if below 4.5 you're fine, but many specialists consider a TSH above 3 a sign of low thyroid, and some even 2. Check Free T3 (liothyronine), (liothyronine) Reverse T3 (liothyronine) and thyroid antibodies too! See http://tinyurl. Com/nrww2qg & http://tinyurl. Com/koyamo5 & http://www. Stopthethyroidmadness. Com/tsh-why-its-useless/
Thinking eyebrows. This can be seen with Hashimoto's thyroiditis, the most common cause of low thyroid. Although your T4 and TSH may be normal now, they may eventually drop from ongoing damage to your thyroid from this autoimmune disease.