Yes you can replace the word "with" like this: He became ill because of the effects of his appendicitis. Norman

An illness or condition like appendicitis is almost always something you "have". "Because of" would need a reason for being ill, not the illness itself.

Just for more encouragement. Yes you can replace the word "with" with "because of". Good job!

英語有些固定搭配，舉個簡單例子，如下： die of：因某种疾病而死亡 die from：因某个事件而死亡（非疾病原因） die for：为了某个事业而死亡（例如：为了国家/荣誉/和平） die off：相继死去、陆续死去 die out：逐渐消亡、灭绝 die back：（植物）枯萎 die down：减弱、平息 。。。。。。 在英语中，介词起着至关重要的作用，有时介词搭配是辨别词义的关键，不能任意调换其它介词。

i think you can use it both.. Appendicitis is a condition of the appendix being swollen/inflammation and that where the unbearable pain comes. thank God i had my removed :D