Infectious causes are many: tuberculosis, syphilis, herpes virus, fungi, parasites (like Toxoplasma) and even Lyme disease. Sometimes infection triggers an immune response in the body, and sometimes it is introduced by trauma. Doctors will do antibody tests, cultures and other checks to confirm which pathogen it is, and then use the corresponding drugs to fight it. The earlier the cause is found, the greater the hope of cure, which is crucial.