Issues

Panniculitis /Steatitis

 

Panniculitis is a term that describes inflammation of the fat-containing tissues just under the skin. An uncommon condition, it’s been identified as a problem in dogs when bacteria, fungi or other organisms infect this area

 

SYSTEMS AFFECTED

Skin/Exocrine

 

SIGNALMENT

Species

Steatitis—predominantly cats, but can occur in dogs with concurrent diseases.

 

Mean Age and Range

Panniculitis—any age.

Steatitis—young to middle-aged cats; older dogs.

 

SIGNS

• Uncommon in dogs and cats.
• Single or multiple subcutaneous nodules or draining tracts.
• May be painful and fluctuant to firm.
• Nodules—few millimeters to several centimeters in diameter.
• Involved fat may necrose.
• Exudate—usually a small amount of oily discharge; yellow-brown to bloody.
• Multiple lesions (dogs and cats)—systemic signs common (e.g., anorexia, pyrexia, lethargy, and depression).

 

CAUSES & RISK FACTORS

• Infectious—bacterial, fungal (deep mycosis or dermatophyte), opportunistic mycobacteria, Nocardia, viral.
• Immune-mediated—lupus panniculitis, erythema nodosum, vasculitis or drug reaction.
• Idiopathic—sterile nodular panniculitis, thromboembolism.
• Trauma.
• Neoplastic—multicentric mast cell tumors, cutaneous lymphoma, pancreatic carcinoma.
• Foreign bodies.
• Post-injection— corticosteroids, vaccines, other subcutaneous injections.
• Nutritional—vitamin E deficiency in cats, oily fish-based diet (steatitis).

 

DIAGNOSIS

DIFFERENTIAL DIAGNOSIS

 

Infectious

• More common than sterile/immune-mediated panniculitis.
• Deep pyoderma.
• FIP.

 

Cutaneous Cyst

• Usually non-painful, non-inflamed
• Well demarcated

 

Lipoma

• Soft; usually well demarcated
• No inflammation or draining tracts
• Usually solitary

 

Mast Cell Tumors/Epitheliotropic Lymphoma

• Multifocal
• Often erythematous
• Variable presentations

 

Sterile Nodular Panniculitis

• Diagnosis made by ruling out other causes of panniculitis.

 

CBC/BIOCHEMISTRY/URINALYSIS

• Panniculitis-no abnormalities.
• Most steatitis cases and occasional panniculitis: moderate to severe neutrophilia with mild eosinophilia; mild to moderate leukocytosis; mild nonregenerative anemia; hypoalbuminemia and proteinuria, possible hypocalcemia.

 

OTHER LABORATORY TESTS

• Antinuclear antibody—lupus panniculitis
• Serum protein electrophoresis
• Serum lipase/amylase levels
• FeLV/FIV testing

 

IMAGING

• Abdominal ultrasound:
• Panniculitis—pancreatitis may be a contributing factor.
• Steatitis—may see mottled subcutaneous, inguinal or falciform fat, loss of contrast in abdominal cavity.

 

DIAGNOSTIC PROCEDURES

• Aspirates and impression smears:
• Pyoderma—numerous neutrophils and variable numbers of mononuclear cells and bacteria.
• Fungal infections – fungal organisms and variable numbers of mononuclear cells may be noted.
• Blastomycosis—urine antigen testing.
• Bacterial culture and sensitivity testing (tissue)—necessary for identifying primary or secondary bacterial infection.
• Fungal and opportunistic mycobacteria culture (tissue).
• Biopsy with negative cultures for diagnosis of sterile nodular panniculitis.
• Special stains of histopathologic samples—may help identify causative agent.

 

PATHOLOGIC FINDINGS

• Surgical excisional biopsies—more accurate than punch biopsy specimens in most cases.
• Histopathology required for diagnosis:
• Panniculitis—lobular or diffuse infiltrate (granulomatous, pyogranulomatous, suppurative, eosinophilic, necrotizing or fibrosing) of panniculus; may identify if vasculitis present. Special stains will aid in identifying infectious agents.
• Steatitis—lumpy, granular fat, normal to yellowish/orange coloration of body fat may be noted.

 

TREATMENT

Diet: Steatitis—remove fish products from diet; feed nutritionally complete, balanced commercially prepared food; may require parenteral feeding (e.g., PEG tube, esophagostomy feeding tube).

 

MEDICATIONS

DRUG(S)

• Positive culture results require appropriate antibacterial, antifungal, or antimycobacterial treatment.

 

• Sterile nodular panniculitis
• Systemic treatment with corticosteroids; prednisone (2.2 mg/kg daily in dogs or 4.4 mg/kg daily in cats: taper based on response: may require low dose to maintain remission).
• Oral vitamin E—200 IU q12h < 10 kg, 400 IU q12h > 10 kg.
• Azathioprine (Dogs: 1 mg/kg PO daily initially)—can be used if corticosteroids are contraindicated or insufficient response to corticosteroids alone.
• Cyclosporine can be beneficial in some dogs (initially 5 mg/kg q24h for 4–8 weeks, then tapered).

Steatitis

Oral vitamin E—200 IU q12h < 10 kg, 400 IU q12h > 10 kg; corticosteroids at an anti-inflammatory dosage; S-adenosylmethionine PO on an empty stomach.

 

FOLLOW-UP

Depends on underlying etiology type and duration of treatment.

Monitor CBC, platelet count, chemistry profile, and urinalysis/urine bacterial culture and sensitivity if immune-suppressive agents or long-term corticosteroids are used.

 

MISCELLANEOUS

ASSOCIATED CONDITIONS

Pancreatic carcinoma, chylous ascites, peritonitis

 

ABBREVIATIONS

FeLV = feline leukemia virus

FIP = feline infectious peritonitis

FIV = feline immunodeficiency virus

PEG tube = percutaneous endoscopically-placed gastrostomy tube

 

Visit your veterinarian as early recognition, diagnosis, and treatment are essential.

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