Hello: Hi and thank you for asking on HCM! I read carefully all your concerns and I can say as follows : In my opinion is not the only thyroid problems that casues muscel crap , Please follow my suggestion: 1.With regards to your symptoms, I can say that your symptoms: muscel cramps unbearable looks like more as hypothyroid symptoms;but not only that . Because: Your concerns is not now, that you take steroid inj.You just say that its happened for years. -I would like to know , in which dose you are taking Synthroid?? -Are you taking the pil in morning with empty stomach? -Which are the last lab test for Thyroid hormone Tsh , Ft3 &Ft4.? Iam telling you some of Hypothyroid Symptoms like ,Fatigue,Weakness,Weight gain or increased difficulty losing weight,Coarse, dry hair ,Dry, rough pale skin,Hair loss,Cold intolerance ,Muscle cramps and frequent muscle aches,Constipation,Memory loss etc Like side effect of steroid is :Muscel wasting ,If you are used for very long –times steroid , waisting of legs (not over all body) musceles may occur. When the steroids are stopped some people experience muscle cramps for a short time. My advise for you : Iam duty to say that are a lot of casues that makes you to feel muscel cramps ;For that reasons I need to know the level • Potassium(Low potassium levels in your blood can cause weakness, fatigue, and abnormal heart rhythms. And than we can find how to treat hypokalemia.) • Sodium (Low blood sodium, or hyponatremia can cause muscle cramps). • PTH level (Hypoparathyroidism also can casuse Muscel cramps) Did you have problem with your Kideny? So you must to check : • Blood test to measurement Kidney function :Creatinine, GFR,Blood urea Nitrogen • Electrolytes test (Sodium,Potasium) • PTH • Ca • Vit B12 I suggest to check all the blood test and than to consoult with the physision . You can consult with Endocrinologies also for thyroid problems. Hope that i have been helpfull. Kind Regars Dr,Klodiana Poshi