As long as you do not include their name, you can most definitely write about the patient, just refer to them as the client or patient. I would not even hesitate to do so because that is valuable experience!
I am in the process of applying now, and will be submitting all applications in the upcoming week. In my letter of intent, I added a brief overview of my clinical experience, and talked about the disorders I have personally worked with in my speech and audiology practicums.
I would add whatever is necessary to differentiate you from other candidates.