Panniculitis

Panniculitis is inflammation of the subcutaneous (underneath the skin) fat tissue which may result from several different causes. It is characterized by deep-seated skin nodules that often become ulcerated and develop draining tracts. Lipocytes (fat cells) can be damaged by many factors resulting in further inflammation and abnormal reactions.

Causes of Panniculitis

The condition has been associated with various vaccines and injection of other medications including antibiotics. It is thought that the inflammation results from a combination of foreign body and hypersensitivity reactions. Traumatic panniculitis occurs when blunt trauma, chronic pressure, or decreased blood supply are present. Infectious panniculitis occurs when bacteria or deep fungal agents become established in the panniculus (a layer of fat beneath the skin).

Immune-mediated Panniculitis

Immune-mediated panniculitis occurs with immune-mediated vascular diseases such as systemic lupus erythematosus and reactions occurring due to drugs, infectious agents, or internal malignancy.

Breeds at Risk

In Dachshunds, Collies and German Shepherd dogs seem to be predisposed to sterile nodular form of panniculitis. Animals with sterile nodular panniculitis are more likely to have multiple lesions.

Signs of Panniculitis

There is no age or sex predilection. Lesions associated with sterile nodular panniculits are most commonly located over the neck and trunk. Some nodules are mobile and some rupture and drain an oily brown or blood-tinged discharge. There may be evidence of scarring in the area of the ruptured nodules, and a secondary staphylococcal infection may occur after rupture. Fever, depression, lethargy, anorexia may be present in dogs with multiple lesions. Sterile foot panniculitis of the German Shepherd dog appears as well-defined tracts that have slightly swollen inflamed borders. They are most frequently located on the footpads.

Diagnosis of Panniculitis

The definitive diagnosis can be made only by biopsy. Skin biopsy reveals inflammation of the subcutaneous fat.

Treatment of Panniculitis

Solitary lesions may be removed surgically. If the panniculitis is due to infectious agents appropriate treatment for the specific agent is administered. Animals with multiple sterile lesions respond well to systemic corticosteroids (2.0 mg/kg q24h) until the lesions have regressed (3 to 8 weeks). Many animals will enter long-term or permanent remission. If lesions recur, long-term alternate dose corticosteroid therapy is prescribed.

In some cases, dogs responded to anti-inflammatory doses of prednisone. The lesions in these dogs relapsed once the levels of steroids were reduced. However, in two of the cases oral vitamin E therapy at a dose of 300 iu twice daily allowed to reduce the amount of steroid drugs. In another case, vitamin E acted to control the clinical signs without steroid therapy.

Prognosis for Panniculitis

Most animals will recover uneventfully if the underlying cause is corrected. Some cases will get recurrences.

Cat Panniculitis
Photo courtesy of Infectious Diseases and Pathology, University of Florida

References:
1. Nesbitt G.E. & Ackerman L.J. Miscellaneous Canine Skin Diseases. In: Canine and Feline Dermatology: Diagnosis and Treatment. Veterinary Learning Systems, Trenton, New Jersey, 1998
2. Scott, Miller & Griffin. Miscellaneous Skin Diseases. In: Small Animal Dermatology. W.B. Saunders, Philadelphia, 1995
3. Sterile idiopathic pedal panniculitis in the German shepherd dog--clinical presentation and response to treatment of four cases.Paterson S. Animal Medical Centre Referral Services, Chorlton, Manchester.