Idiopathic (more than 50 percent of cases)
Radiation therapy
Medications
	Penicillin
	Sulfonamides
	Phenytoin (Dilantin)
	Barbiturates
	Phenylbutazone
Infectious causes
	Herpes simplex virus
	Epstein-Barr virus
	Adenovirus
	Coxsackievirus B5
	Vaccinia virus
	Mycoplasma species
	Chlamydia species
	Salmonella typhi
	Yersinia species
	Mycobacterium tuberculosis
	Histoplasma capsulatum
	Coccidioides immitis