By Malcolm Weir, DVM, MSc, MPH; Tammy Hunter, DVM; Debbie Stoewen DVM, MSW, RSW, PhD

What is panniculitis?

Panniculitis is a localized inflammation of the tissues under the skin, causing a firm swelling (nodule) that may ulcerate and drain fluid. It is a common problem in cats and is less common in dogs.

What causes panniculitis?

In younger animals with a single lump, the cause is often blunt trauma. In cats, panniculitis is often caused by bite wounds from fighting.

Other, much less common causes include:

  • infections
  • immunological reactions
  • steroid treatment
  • diseases of internal organs, such as the pancreas or liver
  • poor nutrition
  • diseases that affect the blood supply

These causes are usually only considered when there are multiple lumps, recurrences of panniculitis, or other signs of disease.

"In cats, panniculitis is often caused by bite wounds from fighting."

What are the clinical signs of panniculitis?

The most obvious sign of panniculitis is a lump. This lump may ulcerate, bleed, and become secondarily infected or put physical pressure on the surrounding tissue structures. As the fat tissue degenerates, toxic substances may enter the bloodstream, causing your pet to have a fever or become depressed. Classic sites for these lumps to develop are on the flanks (the side of the body between the ribs and the hip) of dogs and the abdomen of cats.


How is panniculitis diagnosed?

Although your veterinarian may suspect panniculitis with a history of the rapid appearance of one or more lumps and their location, an accurate diagnosis relies on the microscopic examination of tissue.

" accurate diagnosis relies on the microscopic examination of tissue."

Fine needle aspiration (FNA) may be performed. FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the lump and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

In some cases, results from FNA are not entirely clear and a biopsy may be necessary. A biopsy is the surgical excision of one or more pieces of the lump. The pieces are then examined by a veterinary pathologist under a microscope. This is called histopathology. If the entire lump is removed and submitted for examination, the pathologist can provide the most accurate diagnosis and also assess whether the removal was complete. Histopathology can rule out other diseases, including cancer. Some forms of cancer resemble panniculitis. Because these cancers can be aggressive, early removal and examination of all lumps are important both for an accurate diagnosis and the development of a timely treatment plan.

What are the treatments for panniculitis?

The most common treatment for panniculitis is the surgical removal of the lump. If a secondary infection is present, antibiotic therapy may be needed as well. The goal is to find, treat, and/or remove any underlying cause or trigger of the panniculitis. Some cases of panniculitis are caused by bacteria or fungi and treatment of this underlying (primary) infection is necessary.

"The goal is to find, treat, and/or remove any underlying cause or trigger of the panniculitis."

In cases where there is no obvious cause for the lump(s), immune system-modulating drugs, such as prednisolone, cyclosporine (Atopica®), tetracycline + niacinamide (Gourmeds®), or vitamin E supplementation may be tried.

While the inflammatory response of the body may remove damaged tissue, permanent damage to the area (with scarring and loss of blood supply) may occur. This causes further problems unless the area is surgically removed.

How can I help my pet recover?

It is important to prevent your pet from rubbing, scratching, licking, or biting the lump(s), all of which can cause even further inflammation, itching, infection, ulceration, and bleeding. Any ulcerated area needs to be kept clean. After surgery, the incision site needs to be kept clean and dry and your pet should not be allowed to interfere with the site. Report any loss of sutures or significant swelling or bleeding to your veterinarian. If you require additional advice on post-surgical care, please contact your veterinarian.

How will I know if the panniculitis is permanently cured?

Surgical removal usually offers a complete cure. If the lump is sent for histopathology, the diagnosis can be confirmed, the completeness of excision assessed, and other diagnoses ruled out.

If the condition in your pet is due to one of the rare non-traumatic causes, there may be further lumps or recurrence at the same site within days to weeks. It may be necessary to conduct more diagnostic tests to find the cause and assess how the underlying problem can be cured.

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