Hello – I’m not familiar with the pigment issue…you might mention this to your doctor.
An article from last year in the New England Journal of Medicine noted that hyperthyroidism “may” worsen following RAI, so it appears that not everyone experiences these symptoms.
There is a specific condition called “Radiation Thyroiditis” that occurs in about 1% of patients and causes the thyroid gland to become painfully inflamed. This is generally treated with nonsteroidal anti-inflammatory drugs, so if you continue to have issues, definitely mention this to your doctor.
Take care!