Lymphadenopathy can be brought on by numerous underlying medical conditions. Some are much more serious or severe than others. The cause behind the issue should be figured out as it may require its own course of treatment, aside from the standard lymphadenopathy treatment.

Below are some potential medical causes:

Bacterial infection
Breast cancer
Bubonic plague
Cat scratch disease
Chronic infection
Cytomegalovirus
Dengue
Epstein-Barr virus
Erythroderma
Hairy cell leukemia
Hepatitis A and B
Herpes virus 2
Histoplasmosis
HIV/AIDS
Hodgkin lymphoma
Human African trypanosomiasis
Infectious mononucleosis
Leprosy
Neuroblastoma
Non-Hodgkin lymphoma
Parasitic disease
Radiotherapy
Sarcoidosis
Snake or spider bites
Stomach cancer
Syphilis
Systemic lupus erythematosus (SLE)

Toxoplasmosis
Tuberculous lymphadenitis
Tumors
Tumor metastasis
Typhus fever
Viral infection
Virchow's node
Whipple's disease

In addition to general lymphadenopathy symptoms, others may be present due to the underlying cause. Once a diagnosis of lymphadenopathy is made, it may be possible to begin treatment.