This woman has thinning eyebrows and worries that it may be a sign of hyperthyroidism. She feels fine and wants to avoid thyroxin. Can readers help? Again, some people replied to this in confusion, asking this reader to evaluate whether she's concerned about hypothyroidism and not hyperthyroidism! Thinning eyebrows are usually associated with the former. A simple blood test with your GP would be helpful in ruling out this condition.