Swollen lymph nodes in dogs: lymphadenitis and other causes

Overview

Inflammation is classified by the predominant inflammatory cells in the node. A reactive node becomes activated when antigens from its drainage area, substances recognised by the immune system, trigger a response. An inflamed node may contain neutrophils, eosinophils or macrophages, for example.

Changes may be confined to one area or affect several nodes throughout the body. Nodes within the chest or abdomen can also be affected without visible lumps beneath the skin. Treatment depends on the cause, so enlarged nodes do not all need the same medication.

A reactive node generally contains lymphocytes at different maturity stages, although small cells still predominate. Inflammation and reactive hyperplasia can coexist in one node.

Causes

Local inflammation and infections

A node can itself become inflamed or react to inflammation in its drainage area. Local enlargement may result from a skin infection, wound, foreign body or periodontal disease, for example. A cervical node abscess may involve a foreign body penetrating through the mouth or migrating through tissues.

Causes include certain fungi and protozoa as well as bacteria. Mycobacteria and Leishmania parasites, for example, can cause macrophage-predominant inflammation. Possible infections are assessed according to residence and travel history.

Sterile inflammation and tumour-related changes

In sterile, steroid-responsive lymphadenitis, investigation finds no pathogen or other triggering disease. Juvenile cellulitis is also a sterile inflammatory disease of skin and lymph nodes. A similar skin and lymph node syndrome sometimes affects adults too.

A tumour can cause a node's inflammatory response, and metastasis may coexist with inflammation. An abscess and malignant tumour can also occur in the same node.

Inflammation dominated by macrophages and multinucleated giant cells is called granulomatous. A foreign body reaction may underlie it, so the cell type itself does not name the cause. Neutrophilic inflammation can also accompany vasculitis, skin ulcers, trauma or tissue death.

Risk factors

No single age or breed profile covers every lymphadenitis form because several diseases underlie it. Young females, particularly English Springer Spaniels, appear predisposed to sterile steroid-responsive lymphadenitis. This concerns that form rather than every cause of enlarged nodes.

In a series of 90 adult dogs with sterile dermatitis and lymphadenitis, median onset age was 3.54 years. Ages ranged from 1 to 11.4 years. Travel and importation influence possible infectious exposure, so previous countries of residence and destinations belong in the history.

Typical symptoms

Signs depend on whether changed nodes lie beneath the skin, in the neck or internally.

• Neck swelling or a more obvious lump appears.
• Your dog is tired and cannot join normal activities.
• Appetite decreases and food is left uneaten.
• Fever may accompany lethargy and an obviously unwell appearance.
• The abdomen is tender despite no apparent enlargement of superficial nodes.
• Deep neck swelling can make breathing difficult or noisy.

Sterile skin-associated inflammation may cause facial swelling, pustules, crusts and ulcers. Generalised, painless enlargement may instead be the first finding in lymphoma.

In the 90-dog adult sterile dermatitis and lymphadenitis series, enlarged nodes were found in 33.3%. This is therefore a skin-associated syndrome in which not every dog has visible node enlargement.

Complications and consequences

Abscesses and concurrent disease

An enlarged cervical lesion can involve breathing difficulty. Finding an abscess does not remove the need to investigate a possible underlying tumour. Misdiagnosis can delay treatment of progressive cancer.

In a report of two tumour-associated neck abscesses, one dog was euthanased because of reduced quality of life 6 weeks after surgery. The other was still alive at 388 days after combined treatments. These different tumour outcomes emphasise investigating the underlying disease as well as the abscess.

Recurrence and outlook

Sterile steroid-responsive lymphadenitis can recur after treatment ends. During follow-up of adult sterile dermatitis and lymphadenitis, 19 of 30 dogs remained in remission, without signs. Eleven of the same 30 followed dogs relapsed. These figures concern a particular skin and lymph node syndrome rather than prognosis for every lymphadenitis.

Diagnosis at the vet

Examination and sample selection

Your vet examines your dog overall and assesses whether changes are local or involve several nodes. Mouth, dental and skin examination may identify an inflammatory focus in the node's drainage area. Feeling superficial nodes and checking the mouth and skin form part of a routine health examination.

Fine-needle sampling collects cells for microscopic examination, or cytology. With several enlarged nodes, multiple representative nodes may be sampled. A blood count, biochemistry and urinalysis supplement investigation. If a tumour spreads to lymph nodes, even a normal-sized node may be sampled.

Inflammation type and pathogens

Around 75–95% of normal node cells are small, mature lymphocytes. More than 5% neutrophils may suggest inflammation. Eosinophilic inflammation can relate to hypersensitivity reactions or certain tumours, among other causes. Increased inflammatory cells prompt a search for bacteria, protozoa and fungi. Additional tests may include culture, PCR and antibody testing. An abscess can be tested for both aerobic and anaerobic bacteria.

Blood contamination may increase sample neutrophils, particularly if circulating counts are high too. In eosinophilic inflammation, eosinophils typically exceed 3% of nucleated cells in the node sample. Interpretation therefore considers representativeness and blood contamination as well as cell types.

Small-cell lymphoma can resemble a normal or reactive node microscopically. Distinction may need histology, flow cytometry or PARR, which examines lymphocyte antigen receptor gene rearrangements. Further investigation therefore does not always mean the first sample was collected incorrectly.

Imaging and histology

Ultrasound helps identify the tissue of origin and guide the needle appropriately. Detailed assessment or surgical planning for deep cervical changes may require CT. A sparse, bloody or damaged cell sample may need repeating or replacing with a tissue sample.

Histology shows the whole node's structure as well as cells, helping distinguish difficult changes. No metastasis in a cell sample does not exclude a focus elsewhere in the same node. Sterile lymphadenitis is diagnosed only after possible infections and other underlying diseases have been investigated.

Treatment

Treat the established cause

Your vet chooses treatment according to cytology, histology and other investigation findings. Treating a local inflammatory focus, such as dental or skin disease, forms part of managing reactive enlargement. Antibiotics are not the primary treatment for sterile inflammation: the steroid-responsive form uses immunosuppression after infection is excluded. Other immunosuppressants may be considered with a poor response or severe steroid adverse effects.

Surgical abscess treatment may require removal of the entire affected node. Culture and susceptibility results help target antimicrobial treatment. If a tumour is found, treatment is planned according to its type.

Monitoring recovery

In one Cairn Terrier with sterile lymphadenitis, fever resolved within 48 hours of starting corticosteroids. Appetite returned and abdominal pain was no longer found. Enlarged abdominal nodes had disappeared at ultrasound follow-up 1 month after diagnosis. The dog remained healthy without treatment 2.5 years after presentation. These times describe one dog's follow-up rather than recovery speed for every patient.

In the adult dermatitis and lymphadenitis series, median time to remission was 28 days. Monitoring may also use CRP, a blood marker of systemic inflammation. Dehydration and pain are treated when needed with fluids and veterinary-selected pain relief.

If your dog is well, no other abnormalities are found and a locally enlarged node has normal cytology, monitoring with re-examination after 7–10 days may be selected.

Prevention

The cause of sterile inflammation may remain unknown, preventing cause-specific prevention. Regular health checks can identify hidden skin, ear and dental disease. At least annual checks are recommended even for apparently well dogs.

For travel to a Leishmania-endemic area, protection against sand fly bites reduces infection risk. Plan protection with your vet for the full possible exposure period. This prevents one possible infection rather than every disease causing enlarged nodes.

Leishmaniosis vaccination reduces progression to clinical disease but does not prevent infection itself. Travel-related vaccination and sand fly protection therefore address different aspects of preventing the same infection.

Important for dog owners

Record when the lump was noticed, how it changes and any concurrent skin or mouth signs. Report travel and previous countries of residence because further tests are selected according to geographical exposure. Bring a medication list: individual medicine reactions are also possible underlying causes.

Monitor appetite, alertness, breathing and pain. Sterile lymphadenitis may improve rapidly but can relapse after treatment ends. In one case, checks were scheduled every 3–4 weeks; the appropriate interval depends on your dog's disease. A node remaining enlarged may need a tissue sample to extend the initial investigation.

Frequently asked questions

Are swollen lymph nodes always inflamed?

Enlargement can result from inflammation, reactive changes or a tumour. Lymphadenitis means increased inflammatory cells within the node itself. Lump size or feel therefore cannot establish the cause: examination and often cytology or histology are needed.

Can an inflamed node be inside the abdomen?

Changed nodes may lie beneath the skin, internally or both. Abdominal sterile lymphadenitis can cause pain and fever without superficial node enlargement. Ultrasound can find such changes, which can then undergo image-guided sampling.

Does every enlarged node need antibiotics?

Treatment depends on why it is enlarged. Sterile steroid-responsive lymphadenitis uses immune-modifying treatment after infectious causes are excluded. The same approach therefore cannot apply to a bacterial abscess, tumour and sterile inflammation.

Does an abscess rule out cancer?

An abscess can coexist with a malignant tumour in the same node. An abscess diagnosis therefore should not end investigation for an underlying tumour if other findings raise suspicion. Further testing may need imaging and cytological and histological interpretation.

Can inflammation return after recovery?

Sterile lymphadenitis can relapse after treatment ends. In adult dermatitis and lymphadenitis follow-up, 11 of 30 cases with known remission status relapsed. This is an observation in a particular syndrome rather than a general recurrence rate for all lymphadenitis.