Fatty Layer or Nodule Under the Skin in Cats

Veterinarians refer to a fatty layer that concentrates into a nodule under the skin of cats as feline panniculitis. Panniculitis occurs when the insulating fatty layer under a cat's skin becomes inflamed, causing bumps or nodules to form. These nodules may be soft or firm. They may be tender to the touch and sometimes rupture, bleed or produce a yellow discharge. Cats suffering from a fatty nodule usually recover following surgical treatment and medication.

The main symptom of panniculitis is a localized fatty nodule located anywhere on a cat's body. This lump is sometimes called a "fatty tumor," but is non-cancerous, or benign. Schedule an appointment with your veterinarian if your cat has any of the following:

• One or more fatty lumps anywhere on the body, especially the trunk
• A nodule that is firm or soft to the touch
• A bump that bleeds or discharges a yellow, oily substance
• A lump that produces a pain response with pressure

The lump may or may not be inflamed, red or painful. While these nodules typically appear on the abdomen and trunk, they can also be found on the paw or leg. Once it ruptures, the nodule may scab or crust over. Even if the lump scabs and appears to be healing, it is important to visit your veterinarian to eliminate more serious conditions or prevent subsequent infections or nodules. 

Types 

There are two main types of panniculitis, infectious and sterile.

• Sterile nodular panniculitis, or idiopathic panniculitis, is typically the result of trauma or an underlying medical condition, such as an autoimmune disorder. Sterile panniculitis may also be a reaction to a vitamin deficiency or treatment with certain drugs.
• Infectious panniculitis, or non-idiopathic panniculitis, is caused by inflammation of fatty tissue that has been invaded by infectious agents, such as bacteria or fungus.

Only a veterinarian will be able to diagnose or treat your cat's panniculitis, regardless of the cause or type.

Panniculitis is the result of an inflamed fatty layer under the skin of cats. This inflammation can arise in several contexts, depending on whether the condition's origin is idiopathic or non-idiopathic. The most common causes of panniculitis are:

• Physical trauma, such as an injection or animal bite
• Bacterial or fungal infection of subcutaneous fat
• Autoimmune response
• Treatment with certain drugs, such as steroids
• Pancreatitis, or inflammation of the pancreas
• Vitamin E deficiency

Trauma is, by far, the most common cause of panniculitis. A single fatty nodule under the skin in cats is typically caused by trauma at the site of the lump. Multiple fatty nodules are likely the result of systemic reactions, deficiencies or infections. 

Examination of panniculitis begins with a comprehensive medical history to determine whether your cat has experienced trauma at the site of the nodule. If no trauma is reported or evident, your veterinarian may ask additional questions about the onset of the nodule in an effort to understand any environmental or lifestyle factors that may have contributed to the inflammation. 

Your veterinarian will sample tissue from the fatty nodule to diagnose and discover the cause of your cat's panniculitis. He or she may remove fluid from the nodule with a needle, perform a biopsy, or surgically remove the entire nodule prior to diagnosis. The tissue will be examined under a microscope to determine the cause of the nodule and rule out certain types of cancer.

There are a few panniculitis treatments available. Depending on the cause of your cat's panniculitis, your veterinarian will recommend surgical removal of the lump or antibiotic treatment. A single nodule resulting from simple trauma can be resolved with surgery alone. This surgery has few complications and the prognosis for these cats is generally very good. 

For cats with infectious panniculitis and multiple nodules, surgery to remove the existing nodules is supplemented with medication. Antifungal or antibacterial medication will be prescribed depending on what organism is discovered on microscopic examination of the tissue. Vitamin E supplementation will be administered for panniculitis secondary to a Vitamin E deficiency. These cats also tend to recover completely following treatment of the infection. 

The surgical removal of a fatty nodule usually cures panniculitis. Cats usually recover in as little as three weeks, although scabby or patchy skin may persist at the former site of the nodule. Follow-up appointments should be maintained to ensure complete recovery and prevent infection of the surgical site. 

Occasionally, panniculitis persists following surgical excision and treatment with medication. These more complicated expressions of panniculitis may alert your veterinarian to a more serious, underlying condition. Regular follow-up appointments for tissue sampling and the collection of medical histories are required to determine a course of treatment.