There is also a movement disorder called Sydenham's Chorea that is the result of untreated strep infection. It can involve mood changes as well. My difficult child 2 developed this. His handwriting suddenly deteriorated over a one month period and his behavior and mood got worse. I was glad I saved his spelling tests so I could show the doctors. It took well over a year to get an accurate diagnosis. A neurologist finally examined him and felt choreoathetotic movement in his hands, and a strep titre was checked -- his was 1360. Normal is <=170 for his age. That's what confirmed the diagnosis.
We believe he had the infection while we on vacation one year. His pediatrician called in antibiotics for him because he started running a fever after having had a cough for a week. He took the medications for a few days, but broke out in a rash (likely scarlet fever). I thought the rash was from the medication, so I stopped it. My mistake!
His movement problems have resolved almost completely. This disease does remit and relapse. If he's exposed to strep again or contracts it, the disease will likely come back, and possibly worse. It causes inflammation in the basal ganglia. The body mistakes the cells there for strep proteins and attacks it. It is technically an immune disorder.