I agree with stkitt that potassium deficiency could be a cause of the muscle cramps. I had this problem myself. I've found that the best way to add potassium to one's diet is to buy what is commonly sold (at supermarkets) as "salt substitute". It's actually pure potassium chloride. It should be taken dissolved in water - I put about 1/4 teaspoon in a full glass of water. It tastes terrible, but if you flavor the water with something like Crystal Lite, or use fruit juice instead of water, you get something that tastes like Gatorade (not surprising - this is basically homemade Gatorade). I drink at least one glass a day, and my cramps have disappeared.
I recommend that you NOT take potassium pills. For one thing, the quantity of potassium in one of those pills is very small so you need to take a lot, and they are expensive. Plus the pills have been found to damage the stomach lining, which is the last thing a Crohnie needs.
Crohn's since 1988