Fatty Layer or Nodule Under the Skin in Cats


PetMD Editorial

Published Apr. 19, 2010

Panniculitis in Cats

Panniculitis is a condition where the layer of fat just under the cat's skin (subcutaneous fat tissue) becomes inflamed. Though uncommon, the fatty tissue typically concentrates and affects the trunk area as a single nodule or as multiple nodules. In addition, as a result of secondary infections and other complications, the fat cells within the nodule(s) may die.

Cats of any age, sex, or breed may be affected by panniculitis.

Symptoms and Types

Most cats have a single nodular lesion on the trunk that vary from a few millimeters to several centimeters in diameter. The nodule, which is either firm or soft, is freely movable underneath the skin until fully grown. In some cases, yellow-brown to bloody discharge is excreted from the nodule, while the outer skin may turn red, brown, or yellow in color. The area may be extremely sensitive, especially immediately after rupturing. After the ulcers heal, a scar or crusty layer of skin may form.


Panniculitis may be caused by several factors, including:

  • Trauma
  • Infections (bacterial, fungal, etc.)
  • Immune-mediated diseases (lupus panniculitis, erythema nodosum)
  • Recent subcutaneous injections (corticosteroids, vaccines)
  • Neoplastic diseases (multicentric mast cell tumors, cutaneous lymphosarcoma)


You will need to give the veterinarian a thorough history of your cat’s health, including the onset and nature of the symptoms. He or she will then perform a complete physical examination, as well as a biochemistry profile. However, other than the presence of a mass or nodule beneath the skin, most cats will not demonstrate other complications.

Depending on the underlying cause, other diagnostic procedures may be used to rule our other diseases/conditions. For example, the number of white blood cells on a CBC (complete blood count) typically rises in case of infection and help veterinarian determine the type, duration, and severity of infection. Your veterinarian will also usually take a sample directly from the nodule and send it to a pathologist for culture and sensitivity, which helps in determining the type of causative organism (bacteria, fungi) and the suitable course of treatment.


Often, the preferred method of treatment is surgery, especially if only a single nodule is present. However, in case of multiple nodules, a combination of surgery and medication works well. For example, if fungal or bacterial infections are involved, antifungal and  antibacterial medications will be administered, respectively.

If no organism has found to be the cause of the panniculitis -- also called a sterile nodule -- your veterinarian will prescribe steroids, to aid in the regression of the nodule. Vitamin E can also be given in mild cases.

Living and Management

Overall prognosis for cats with panniculitis is often good after treatment. In some cases, it takes just three to six weeks for the nodule(s) to completely regress. Your veterinarian will ask that you bring in the cat for regular follow-up exams, where he or she will conduct routine laboratory tests to monitor the progress of the treatment. This is especially true if steroids are being used to regress the nodule(s).

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