Lymph nodes or 'glands' or "nodes" or "lymphoid tissue" are nodular bodies located throughout the body but clustering in certain areas such as the armpit, back of the neck and the groin. They are part of the lymphatic system.

The lymphatic system is part of the body's immune surveillance system. Blood contains fluid and blood cells. The fluid, which may contain suspended foreign material such as bacteria and viruses, seeps through blood vessel walls into the tissues, where it bathes the body cells and exchanges substances with them. Some of this fluid is then taken up by lymphatic vessels and passed back to the heart, where it is again mixed with the blood. On its way the fluid passes through the lymph nodes. If nodes detect something foreign passing through them such as a bacterium or a cancer cell they will swell up. This is called "lymphadenopathy" or "swollen glands". Usually this is localised (for example an infected spot on the scalp will cause lymph nodes in the neck on that same side to swell up), but when it is in two or more regions, it is called "generalized lymphadenopathy".

Usually this is in response to a body-wide infectious disease such as influenza and will go away once the person has recovered, but sometimes it can persist long-term, even when there is no obvious cause of disease. This is then called "persistent generalized lymphadenopathy" (PGL).

Some patients have no symptoms, spontaneous remission, or a relapsing/remitting course, making it difficult to decide whether therapy is needed. In 2002, authors from Sapienza University of Rome stated on the basis of a comprehensive literature review that "clinical observation without treatment is advisable when possible."

Therapeutic options include surgery, radiation therapy, and chemotherapy. Surgery is used to remove single lymph nodes, central nervous system lesions, or localized cutaneous disease. In 2014, Dalia and colleagues wrote that for patients with extensive or systemic Rosai–Dorfman disease, "a standard of care has not been established" concerning radiotherapy and chemotherapy.

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

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.

Mediastinal lymphadenopathy or mediastinal adenopathy is an enlargement of the Mediastinal lymph nodes

Inguinal lymphadenopathy causes swollen lymph nodes in the groin area. It can be a symptom of infective or neoplastic processes.

Infective aetiologies include Tuberculosis, HIV, non-specific or reactive lymphadenopathy to recent lower limb infection or groin infections. Another notable infectious cause is Lymphogranuloma venereum, which is a sexually transmitted infection of the lymphatic system. Neoplastic aetiologies include lymphoma, leukaemia and metastatic disease from primary tumours in the lower limb, external genitalia or perianal region and melanoma.

Persistent generalized lymphadenopathy (PGL) is enlarged painful lymph nodes occurring in a couple of different areas for more than three to six months for which no other reason can be found. This condition occurs frequently in people in the latency period of HIV/AIDS.

The lymphatic system is part of the immune surveillance system. Blood contains fluid and blood cells. The fluid, which may contain suspended foreign material such as bacteria and viruses, seeps through blood vessel walls into the tissues, where it bathes the body cells and exchanges substances with them. Some of this lymph fluid is then taken up by lymphatic vessels and passed back to the heart, where it is again mixed with the blood. On its way, the fluid passes through the lymph nodes, small nodular organs located throughout the body but concentrated in certain areas such as the armpits or groin. These lymph nodes are also known as "glands" or "lymphoid tissue". If they detect something foreign passing through them, they enlarge. This is called "lymphadenopathy" or "swollen glands". Usually this is localized (for example, an infected spot on the scalp will cause lymph nodes in the neck on that same side to swell). However, when two or more lymph node groups are involved, it is called "generalized lymphadenopathy". Usually this is in response to a significant systemic disease and will subside once the person has recovered. Sometimes it can persist long-term, even when no explanation for the lymphadenopathy can be found.

PGL is often found in cases of autoimmune disease (where the body is attacking itself). These include diseases such as rheumatoid arthritis, lupus and sarcoidosis. Some forms of cancer will also cause PGL. Sometimes, despite exhaustive investigation, no cause for PGL is found. For the patient and the physician, this can continue to be a source of concern, but many adults have had PGL all their lives and suffered no ill effects. In others, the PGL may persist for a decade or more and then mysteriously subside. Children often have generalized lymphadenopathy of the head and neck, or even PGL, without the finding of a sinister cause. At puberty this usually disappears.

The immune system of some people may be sensitized by exposure to a living exogenous irritant such as a bacterial or viral infection, which then results in PGL after the organism has been cleared from the body. In some cases the sensitization is caused by non-living exogenous irritants such as cyclic hydrocarbons (for example, resinous vapours) or pesticides and herbicides.

Axillary lymphadenopathy is lymphadenopathy of the axillary lymph nodes.

Large doses of glucocorticoids are the treatment of choice, and are administered until the signs have resolved. In uncomplicated cases, this can take up to a month. If dogs are not treated promptly and with high doses of steroids, severe scarring may occur. If there is evidence of secondary bacterial infection, treatment with antibiotics is required.

Simple surgical excision is considered curative. Rare recurrences have been reported.

Bilateral hilar lymphadenopathy is a bilateral enlargement of the lymph nodes of pulmonary hila. It is a radiographic term that describes the enlargement of mediastinal lymph nodes and is most commonly identified by a chest x-ray.

In 2016 the Histiocyte Society proposed a classification of histiocytoses into five groups designated by letters: "C," "H," "L," "M," and "R." Group "R" included Rosai–Dorfman disease and "miscellaneous noncutaneous, non-Langerhans cell histiocytoses." Rosai–Dorfman disease itself was classified into "Familial," "Classical (nodal)," "Extranodal," "Neoplasia-associated," and "Immune disease-associated" subtypes.

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.

PTGC is treated by excisional biopsy and follow-up. It may occasionally recur and in a small proportion of patients has been reported to subsequently develop Hodgkin lymphoma (usually nodular lymphocyte predominant Hodgkin lymphoma).

To diagnose this condition, scans or other imaging tests are used. Enlarged nodes in the vicinity of cancer areas could potentially contain cancer.

Probable patients are observed for few weeks until the cause of lymphadenopathy becomes obvious and they are instructed to return to the doctor if there is increase in node size. Biopsy should be performed in case tests suggest malignancy.

The following are causes of BHL:

- Sarcoidosis

- Infection

- Tuberculosis

- Fungal infection

- Mycoplasma

- Intestinal Lipodystrophy (Whipple's disease)

- Malignancy

- Lymphoma

- Carcinoma

- Mediastinal tumors

- Inorganic dust disease

- Silicosis

- Berylliosis

- Extrinsic allergic alveolitis

- Such as bird fancier's lung

- Less common causes also exist:

- Eosinophilic granulomatosis with polyangiitis

- Human immunodeficiency virus

- Extrinsic allergic alveolitis

- Adult-onset Still's disease

Treatment involves antibiotics and may involve drainage of the buboes or abscesses by needle aspiration or incision. Further supportive measure may need to be taken: dilatation of the rectal stricture, repair of rectovaginal fistulae, or colostomy for rectal obstruction.

Common antibiotic treatments include: tetracycline (doxycycline) (all tetracyclines, including doxycycline, are contraindicated during pregnancy and in children due to effects on bone development and tooth discoloration), and erythromycin. Azithromycin is also a drug of choice in LGV.

Cervical lymphadenopathy refers to lymphadenopathy of the cervical lymph nodes (the glands in the neck). The term "lymphadenopathy" strictly speaking refers to disease of the lymph nodes, though it is often used to describe the enlargement of the lymph nodes. Similarly, the term "lymphadenitis" refers to inflammation of a lymph node, but often it is used as a synonym of lymphadenopathy.

Cervical lymphadenopathy is a sign or a symptom, not a diagnosis. The causes are varied, and may be inflammatory, degenerative, or neoplastic. In adults, healthy lymph nodes can be palpable (able to be felt), in the axilla, neck and groin. In children up to the age of 12 cervical nodes up to 1 cm in size may be palpable and this may not signify any disease. If nodes heal by resolution or scarring after being inflamed, they may remain palpable thereafter. In children, most palpable cervical lymphadenopathy is reactive or infective. In individuals over the age of 50, metastatic enlargement from cancers (most commonly squamous cell carcinomas) of the aerodigestive tract should be considered.

As with all STIs, sex partners of patients who have LGV should be examined and tested for urethral or cervical chlamydial infection. After a positive culture for chlamydia, clinical suspicion should be confirmed with testing to distinguish serotype. Antibiotic treatment should be started if they had sexual contact with the patient during the 30 days preceding onset of symptoms in the patient. Patients with a sexually transmitted disease should be tested for other STDs due to high rates of comorbid infections. Antibiotics are not without risks and prophylaxtic broad antibiotic coverage is not recommended.

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

Intranodal palisaded myofibroblastoma, abbreviated IPM, is a rare primary tumour of lymph nodes, that classically presents as an inguinal mass.

It afflicts predominantly males of middle age.

Cervical lymphadenopathy can be thought of as "local" where only the cervical lymph nodes are affected, or "general" where all the lymph nodes of the body are affected.

Acute GPP typically requires inpatient management including both topical and systemic therapy, and supportive measures. Systemic glucocorticoid withdrawal is a common causative agent. Withdrawal or administration of certain drugs in the patient's previous medication regimen may be required. Oral retinoids are the most effective treatment, and are considered first line. Cyclosporine or infliximab may be required for particularly acute cases.

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.

The disorder typically appears among young girls and adolescents but cases in children as young as 17 months have been reported.