What Causes Brownish Flakes Attached To The Scalp?

I am 60 years old and have pustular psoriasis on the soles of my foot. I am taking Humera and Soriatane 25m. 2 days ago while washing my hair I felt a very small bump on the top of my head. It looked very flaky, brownish, no pain, no itch. Today I looked at it real carefully and pulled out what I think were flakes, brownish, very attached to my scalp which left my scalp red. I have been reading alot about this today and lice seems to be one of the reasons. I know I don't have scalp psoriasis. Can the medication cause it? I do have hair loss due to Soriatane. 5'2" and weigh 108 Thank you, Jenny