Lymph node enlargement is recognized as a common sign of infectious, autoimmune, or malignant disease. Examples may include:

- Reactive: acute infection ("e.g.," bacterial, or viral), or chronic infections (tuberculous lymphadenitis, cat-scratch disease).

- The most distinctive sign of bubonic plague is extreme swelling of one or more lymph nodes that bulge out of the skin as "buboes." The buboes often become necrotic and may even rupture.

- Infectious mononucleosis is an acute viral infection caused by Epstein-Barr virus and may be characterized by a marked enlargement of the cervical lymph nodes.

- It is also a sign of cutaneous anthrax and Human African trypanosomiasis

- Toxoplasmosis, a parasitic disease, gives a generalized lymphadenopathy ("Piringer-Kuchinka lymphadenopathy").

- Plasma cell variant of Castleman's disease - associated with HHV-8 infection and HIV infection

- Mesenteric lymphadenitis after viral systemic infection (particularly in the GALT in the appendix) can commonly present like appendicitis.

Less common infectious causes of lymphadenopathy may include bacterial infections such as cat scratch disease, tularemia, brucellosis, or prevotella.

- Tumoral:

- Primary: Hodgkin lymphoma and non-Hodgkin lymphoma give lymphadenopathy in all or a few lymph nodes.

- Secondary: metastasis, Virchow's Node, neuroblastoma, and chronic lymphocytic leukemia.

- Autoimmune: systemic lupus erythematosus and rheumatoid arthritis may have a generalized lymphadenopathy.

- Immunocompromised: AIDS. Generalized lymphadenopathy is an early sign of infection with human immunodeficiency virus (HIV), the virus that causes acquired immunodeficiency syndrome (AIDS). "Lymphadenopathy syndrome" has been used to describe the first symptomatic stage of HIV progression, preceding a diagnosis of AIDS.

- Bites from certain venomous snakes such as the pit viper

- Unknown: Kikuchi disease, progressive transformation of germinal centers, sarcoidosis, hyaline-vascular variant of Castleman's disease, Rosai-Dorfman disease, Kawasaki disease, Kimura disease

It is not lethal in nature and is responsive to tetracycline or ciprofloxacin. Surgical treatment include rhinoplasty. However, if left untreated the disease can lead to sepsis, bleeding, or other chronic conditions that can be fatal.

It is caused by "Klebsiella rhinoscleromatis"—subspecies of

"Klebsiella pneumoniae"— a gram-negative, encapsulated, nonmotile, rod-shaped bacillus (diplobacillus), member of the Enterobacteriaceae family. It is sometimes referred to as the "Frisch bacillus," named for Anton von Frisch who identified the organism in 1882. It is contracted directly by droplets or by contamination of material that is subsequently inhaled.

Lymphadenopathy or adenopathy is disease of the lymph nodes, in which they are abnormal in size, number, or consistency. Lymphadenopathy of an inflammatory type (the most common type) is lymphadenitis, producing swollen or enlarged lymph nodes. In clinical practice, the distinction between lymphadenopathy and lymphadenitis is rarely made and the words are usually treated as synonymous. Inflammation of the lymphatic vessels is known as lymphangitis. Infectious lymphadenitides affecting lymph nodes in the neck are often called scrofula.

The term comes from the word lymph and a combination of the Greek words , "adenas" ("gland") and , "patheia" ("act of suffering" or "disease").

Lymphadenopathy is a common and nonspecific sign. Common causes include infections (from minor ones such as the common cold to dangerous ones such as HIV/AIDS), autoimmune diseases, and cancers. Lymphadenopathy is also frequently idiopathic and self-limiting.

The cause of juvenile cellulitis is unknown. Cytologic examination of aspirates of affected lymph nodes, pustules, abscesses, and joint fluid rarely reveal bacteria, and culture results of intact lesion are always negative for bacterial growth, suggesting a nonbacterial etiology. As signs resolve following treatment with glucocorticoids, the cause is likely to be an immune disorder.

Acute infectious thyroiditis is very rare, with it only accounting for about 0.1–0.7% of all thyroiditis. Large hospitals tend to only see two cases of AIT annually. For the few cases of AIT that are seen the statistics seem to show a pattern. AIT is found in children and young adults between the ages of 20 and 40. The occurrence of the disease in people between 20 and 40 is only about 8% with the other 92% being in children. Men and women are each just as likely to get the disease. If left untreated, there is a 12% mortality rate.

Adenitis is a general term for an inflammation of a gland. Often it is used to refer to lymphadenitis which is the inflammation of a lymph node.

Prognosis is highly variable. Spontaneous remission is common. Complete cure can be obtained with proper antibiotic treatments to kill the causative bacteria, such as tetracycline, doxycycline, or erythromycin. Prognosis is more favorable with early treatment. Bacterial superinfections may complicate course. Death can occur from bowel obstruction or perforation, and follicular conjunctivitis due to autoinoculation of infectious discharge can occur.

Genital elephantiasis or esthiomene, which is the dramatic end-result of lymphatic obstruction, which may occur because of the strictures themselves, or fistulas. This is usually seen in females, may ulcerate and often occurs 1–20 years after primary infection.

Fistulas of, but not limited to, the penis, urethra, vagina, uterus, or rectum. Also, surrounding edema often occurs. Rectal or other strictures and scarring. Systemic spread may occur, possible results are arthritis, pneumonitis, hepatitis, or perihepatitis.

"Lymph adenitis" or "lymph node adenitis" is caused by infection in lymph nodes. The infected lymph nodes typically become enlarged, warm and tender. A swelling of lymph nodes due to growth of lymph cells is called lymphadenopathy. Types include:

- Neck

- Cervical adenitis is an inflammation of a lymph node in the neck.

- Tuberculous adenitis (scrofula) is a tuberculous infection of the skin of the neck caused by "Mycobacterium tuberculosis". Non-tuberculous adenitis can also be caused by "Mycobacterium scrofulaceum" or "Mycobacterium avium".

- Abdomen

- Mesenteric adenitis is an inflammation of the mesenteric lymph nodes in the abdomen. It can be caused by the bacterium "Yersinia enterocolitica". If it occurs in the right lower quadrant, it can be mistaken for acute appendicitis, often preceded by a sore throat.

Lymphangitis is an inflammation or an infection of the lymphatic channels that occurs as a result of infection at a site distal to the channel. The most common cause of lymphangitis in humans is "Streptococcus pyogenes" (Group A strep), although it can also be caused by the fungus "Sporothrix schenckii". Lymphangitis is sometimes mistakenly called "blood poisoning". In reality, "blood poisoning" is synonymous with "sepsis".

Signs and symptoms include a deep reddening of the skin, warmth, lymphadenitis (inflammation of a lymphatic gland), and a raised border around the affected area. The person may also have chills and a high fever along with moderate pain and swelling. A person with lymphangitis should be hospitalized and closely monitored by medical professionals.

Lymphangitis is the inflammation of the lymphatic vessels and channels. This is characterized by certain inflammatory conditions of the skin caused by bacterial infections. Thin red lines may be observed running along the course of the lymphatic vessels in the affected area, accompanied by painful enlargement of the nearby lymph nodes.

When the inferior limbs are affected, the redness of the skin runs over the great saphenous vein location and confusion can be made with a thrombophlebitis.

Chronic lymphangitis is a cutaneous condition that is the result of recurrent bouts of acute bacterial lymphangitis.

Tuberculous lymphadenitis (or tuberculous adenitis) is a chronic specific granulomatous inflammation of the lymph node with caseation necrosis, caused by infection with "Mycobacterium tuberculosis" or "Mycobacterium bovis".

The characteristic morphological element is the tuberculous granuloma (caseating tubercule). This consists of giant multinucleated cells and (Langhans cells), surrounded by epithelioid cells aggregates, T cell lymphocytes and fibroblasts. Granulomatous tubercules eventually develop central caseous necrosis and tend to become confluent, replacing the lymphoid tissue.

Incision drainage with proper evacuation of the fluid followed by anti-tubercular medication.

Juvenile cellulitis, also known as puppy strangles or juvenile pyoderma, is an uncommon disease of dogs. Symptoms include dermatitis, lethargy, depression and lameness. When puppies are first presented with what appears to be staphylococcal pyoderma, juvenile cellulitis, a relatively rare condition, may not be considered.

Despite the thyroid gland being extremely resistant to infection, it is still susceptible to infection by various bacteria. The cause can be almost any bacterium. "Staphylococcus aureus", "Streptococcus pyogenes", "Staphylococcus epidermidis", and "Streptococcus pneumoniae" in descending order are the organisms most commonly isolated from acute thyroiditis cases in children. Other aerobic organisms are "Klebsiella sp", "Haemophilus influenza", "Streptococcus viridans", "Eikenella corrodens", "Enterobacteriaceae", and "salmonella sp".

Occurrences of AIT are most common in patients with prior thyroid disease such as Hashimoto's thyroiditis or thyroid cancer. The most common cause of infection in children is a congenital abnormality such as pyriform sinus fistula. In most cases, the infection originates in the piriform sinus and spreads to the thyroid via the fistula. In many reported cases of AIT the infection occurs following an upper respiratory tract infection. One study found that of the reported cases of AIT, 66% occurred after an acute illness involving the upper respiratory tract. Although the rates of infection are still very low, cases of AIT have been on the rise in recent years due to the higher occurrence of immune-compromised patients.

Other causes of AIT are commonly due to contamination from an outside source and are included below.

- Repeated fine needle aspirates

- Perforation of esophagus

- Regional infection

Paraproctitis is a purulent inflammation of the cellular tissues surrounding the rectum. The most frequent cause is penetration of bacterial flora from the rectum into the surrounding cellular tissues, which may occur through an anal fissure. The inflammation is sometimes limited to the formation of an abscess, and in some cases it spreads for a considerable distance and may be complicated by sepsis.

The symptoms are acute pain in the rectal region, tenderness during defecation, elevated body temperature, and the appearance of an infiltrate in the anal region or on the buttocks. An unlanced abscess may burst and a fistula form. The disease becomes chronic after recurrences. Treatment includes administration of antibiotics and anti-inflammatory agents and, in the suppurative stage, surgical lancing of the abscess.

The symptoms of strep throat usually improve within three to five days, irrespective of treatment. Treatment with antibiotics reduces the risk of complications and transmission; children may return to school 24 hours after antibiotics are administered. The risk of complications in adults is low. In children, acute rheumatic fever is rare in most of the developed world. It is, however, the leading cause of acquired heart disease in India, sub-Saharan Africa and some parts of Australia.

Complications arising from streptococcal throat infections include:

- Acute rheumatic fever

- Scarlet fever

- Streptococcal toxic shock syndrome

- Glomerulonephritis

- PANDAS syndrome

- Peritonsillar abscess

- Cervical lymphadenitis

- Mastoiditis

The economic cost of the disease in the United States in children is approximately $350 million annually.

"Listeria monocytogenes" infection in infants can cause potentially fatal disseminated granulomas, called granulomatosis infantiseptica, following "in utero" infection.

Strep throat is caused by group A beta-hemolytic streptococcus (GAS or S. pyogenes). Other bacteria such as non–group A beta-hemolytic streptococci and fusobacterium may also cause pharyngitis. It is spread by direct, close contact with an infected person; thus crowding, as may be found in the military and schools, increases the rate of transmission. Dried bacteria in dust are not infectious, although moist bacteria on toothbrushes or similar items can persist for up to fifteen days. Contaminated food can result in outbreaks, but this is rare. Of children with no signs or symptoms, 12% carry GAS in their pharynx, and, after treatment, approximately 15% of those remain positive, and are true "carriers".

Crohn's disease is an inflammatory condition of uncertain cause characterized by severe inflammation in the wall of the intestines and other parts of the abdomen. Within the inflammation in the gut wall, granulomas are often found and are a clue to the diagnosis.

Scrofuloderma (also known as "Tuberculosis cutis colliquativa") is a skin condition caused by tuberculous involvement of the skin by direct extension, usually from underlying tuberculous lymphadenitis.

There are several risk factors that increase the likelihood of developing bacteremia from any type of bacteria. These include:

- HIV infection

- Diabetes Mellitus

- Chronic hemodialysis

- Solid organ transplant

- Stem cell transplant

- Treatment with glucocorticoids

- Liver failure

When the lymphatic impairment becomes so great that the lymph fluid exceeds the lymphatic system's ability to transport it, an abnormal amount of protein-rich fluid collects in the tissues. Left untreated, this stagnant, protein-rich fluid causes tissue channels to increase in size and number, reducing oxygen availability. This interferes with wound healing and provides a rich culture medium for bacterial growth that can result in infections: cellulitis, lymphangitis, lymphadenitis and in severe cases, skin ulcers. It is vital for lymphedema patients to be aware of the symptoms of infection and to seek immediate treatment, since recurrent infections or cellulitis, in addition to their inherent danger, further damage the lymphatic system and set up a vicious circle.

In rare cases, lymphedema can lead to a form of cancer called lymphangiosarcoma, although the mechanism of carcinogenesis is not understood. Lymphedema-associated lymphangiosarcoma is called Stewart-Treves syndrome. Lymphangiosarcoma most frequently occurs in cases of long-standing lymphedema. The incidence of angiosarcoma is estimated to be 0.45% in patients living 5 years after radical mastectomy. Lymphedema is also associated with a low grade form of cancer called retiform hemangioendothelioma (a low grade angiosarcoma).

Since lymphedema is disfiguring, causing difficulties in daily living and can lead to lifestyle becoming severely limited, it may also result in psychological distress.

Gram negative bacterial species are responsible for approximately 24% of all cases of healthcare-associated bacteremia and 45% of all cases of community-acquired bacteremia. In general, gram negative bacteria enter the bloodstream from infections in the respiratory tract, genitourinary tract, gastrointestinal tract, or hepatobiliary system. Gram-negative bacteremia occurs more frequently in elderly populations (65 years or older) and is associated with higher morbidity and mortality in this population.

"E.coli" is the most common cause of community-acquired bacteremia accounting for approximately 75% of cases. E.coli bacteremia is usually the result of a urinary tract infection. Other organisms that can cause community-acquired bacteremia include "pseudomonas aeruginosa", "klebsiella pneumoniae", and "proteus mirabilis". "Salmonella" infection, despite mainly only resulting in gastroenteritis in the developed world, is a common cause of bacteremia in Africa. It principally affects children who lack antibodies to Salmonella and HIV+ patients of all ages.

Among healthcare-associated cases of bacteremia, gram negative organisms are an important cause of bacteremia in the ICU. Catheters in the veins, arteries, or urinary tract can all create a way for gram negative bacteria to enter the bloodstream. Surgical procedures of the genitourinary tract, intestinal tract, or hepatobiliary tract can also lead to gram negative bacteremia. "Pseudomonas" and "enterobacter" species are the most important causes of gram negative bacteremia in the ICU.

In pathology, dermatopathic lymphadenopathy, also dermatopathic lymphadenitis, is lymph node pathology due to skin disease.