There are many ways to express yourself. In expressing myself, I share myself; I organize my thoughts about something well enough to write them or speak them. Sometimes my expressions are wordless. Sometimes I express a part of me by singing or doing artwork. Each mode of expression gives "voice" to something that's going on inside of me.
My favorite form of expression would be writing and doing artwork. I believe that God has given me these gifts to whatever degree I may claim them as mine. I believe that surely He has gifted me (I cannot take credit for ANY gift that He has given) for my own benefit in that it is - I believe - very healing to engage in your giftings.
If you have Parkinson's Disease, or any other disorder, take a little while and ponder, "What are my giftings?" Some of us have more gifts than others, but I believe that God has given everybody something. If your disease makes it hard to engage your gifts, then get creative! Ask God to show you how to put the gifts He has given you to good use for both yourself and for others. He will do it. And remember, even if your body won't cooperate with you, think of things you CAN do.
I knew a woman who was wheelchair bound. The last year of her life she was bed-ridden. She was completely paralyzed. She couldn't even cough to clear her lungs. She was a psychologist by trade and continued to counsel people professionally well into her last few months. She decided she wanted to write a book, but that was going to be difficult since she couldn't write and she couldn't talk due to a tracheotomy. I volunteered to write down - word for word - what she wanted her book to say - as she mouthed her words. A dear friend of hers helped also. We both did the transcribing, and the book was finished before she went home to be with the Lord.
Find a way to use your gifts. Don't neglect using them and don't say you don't have any. Show the Giver of all good gifts your gratitude by giving what you can.