There are a cluster of autoimmune diseases more commonly seen with Hashimoto's thyroiditis due to genetic factors. The listed % of risk for another autoimmune disease if you already have one is, from what I've read, 14% to 25%. From the list below I have pernicious anaemia, vitiligo, alopecia areta, Hashimoto's thyroiditis. My Hashi's showed up last decades later.
Excerpt from the book "The Everything Guide To Thyroid Disease" by Theodore C. Friedman, MD, PhD and Winnie Yu Scherer:
"Although the majority of people with Hashimoto's will not develop any other disorders, it's important to know what some of these autoimmune conditions are in case you do start to experience symptoms. Keep in mind, too, that you may be more likely to develop Hashimoto's if you have one of these other conditions.
Type 1 diabetes
Systematic Lupus Erthematosus (SLE)
Inflammatory Bowel Disease
Multiple Sclerosis (MS)"
If you have one autoimmune disease, there are chances to develop other autoimmune diseases, unless if you don't take yourself very well. Food matters the most,follow a healthy diet. Try to reduce the inflammation, just listen to your body to do good for your body. Clean up the gut. Some supplements may help you to reduce the inflammation, zinc, selenium, magnesium,Glutamine, probiotics and a good quality fish oil. Try to eat some fermented food. And of course try to smile:)