Page 59 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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6.6 Panniculitis
VetBooks.ir Inflammation of the subcutaneous adipose tissue.

Clinical features
• Presenting in form of solitary or multiple, firm to fluctuant, raised, well demarcated
lesions.
• Sites of prevalence include dorsal trunk, neck and proximal limbs.
• It can be sterile or secondary to an underlying infectious disease.
• Sterile panniculitis: can be due to a localized or systemic disease. Focal areas of
sterile panniculitis are usually caused by trauma, foreign bodies, vaccination/
injection reactions. Multiple lesions are often associated with a systemic condi-
tion. Possible causes include immune- mediated diseases, drug reactions, pancreatitis,
nutritional deficiencies (e.g. vitamin E) and idiopathic disease.
• Infectious panniculitis: can be caused by bacteria (including Mycobacterium
spp.), protozoa (e.g. Leishmania spp.) and fungi.
• Solitary lesions respond to surgical excision and are associated with good prognosis.
• Over-represented canine breeds (for idiopathic sterile panniculitis): Dachshund,
Miniature Poodle, Collie, Australian Shepherd, Brittany, Dalmatian, Pomeranian
and Chihuahua.

Cytological features
• Cellularity is variable, often adequate.
• Background: characterized by numerous variable-sized, clear fat droplets. Often pale baso-
philic (proteinaceous), it might be variably haemodiluted.
• Amorphous foreign material (e.g. mineral salts) may be seen in panniculitis secondary to
drug injections.
• The type of inflammation depends on the underlying cause and duration of the process.
Macrophages are most frequently seen. They typically contain numerous small, clear punc-
tate vacuoles of lipids, and occasionally small amorphous phagosomes. Multinucleated cells
can be present.
• Neutrophils are seen in acute processes and in association with bacterial infection.
• Small lymphocytes may be numerous, especially in lesions associated with vaccine/injection
reaction.
• Reactive fibroblasts are frequently present intermingled with the inflammatory cells.
• Variable numbers of mature adipocytes, intact or necrotic, can be present.

Differential diagnoses
• Xanthoma (rare)
• Liposarcoma