JPC SYSTEMIC PATHOLOGY
Signalment (JPC #1945775): 6-year-old female Yorkshire terrier
HISTORY: This dog developed multiple skin nodules over an eight-month period.
HISTOPATHOLOGIC DESCRIPTION: Haired skin (3 sections): Expanding the deep dermis and subcutis; separating deep hair follicles and subcuticular adipocytes; and infiltrating the panniculs carnosus are multiple coalescing nodules composed of numerous epithelioid macrophages, neutrophils, lymphocytes, and fewer reactive fibroblasts with scant fibrous connective tissue. This inflammatory infiltrate extends through the panniculus carnosus and often separates and surrounds skeletal muscle fibers, which are atrophied or occasionally swollen and pale with vacuolated sarcoplasm and loss of cross striations (degenerate). In the less affected superficial dermis there are multifocal periadnexal and perivascular infiltrates of low numbers of lymphocytes and plasma cells with rare eosinophils, as well as dilated lymphatics and increased clear space separating collagen bundles (edema). Few hair follicles in the superficial dermis are ectatic and filled with keratin. Apocrine glands are mildly ectatic.
MORPHOLOGIC DIAGNOSIS: Haired skin and subcutis: Panniculitis, nodular, granulomatous, multifocal to coalescing, marked, Yorkshire terrier, canine.
CONDITION: Idiopathic sterile nodular panniculitis
- Idiopathic sterile nodular panniculitis is a diagnosis of exclusion seen rarely in young dogs (less than one year of age), horses and cats
- Breed predilection:
- Some of the older literature reports that dachshunds and poodles are over-represented; more recent publications favor Australian shepherds, Brittany spaniels, Dalmatians, Pomeranians and Chihuahuas
- There is some disagreement in the literature regarding the occurrence of concurrent systemic disease: Older studies report several potential concurrent systemic diseases (pancreatic disease; liver disease; protein losing enteropathy; arthropathy; renal disease; systemic lupus erythematosus; inflammatory bowel disease; keratoconjuncitivis sicca), while according to a more recent study, 82% of affected animals had no concurrent systemic disease identified (the remaining 18% had concurrent arthritis)
- Pyogranulomatous dermatitis and panniculitis caused by intracellular protozoan parasite Caryospora bigenetica reported in Rottweiler puppy
- Single report of concurrent Bartonella henselae infection in a dog with panniculitis and owner with ulcerated nodular skin lesions
- Possibly pancreatic enzyme induced
TYPICAL CLINICAL FINDINGS:
- Single or multiple subcutaneous nodules or plaques, especially on the head and extremities; range in size from 0.5 to several centimeters in diameter and may protrude above the surface of the skin
- Intermittent anorexia, depression, lethargy, and pyrexia with elevated alkaline phosphatase, hypoglycemia, hypoalbuminemia, and neutrophilia depending on concurrent disease
TYPICAL GROSS FINDINGS:
- Nodules may be firm and well circumscribed or soft and ill-defined; typically on the trunk
- Lesions may become cystic, ulcerate, and develop draining tracts that discharge an oily, yellowish‑brown to bloody substance
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Nodular inflammation in the panniculus with mainly macrophages and neutrophils that progresses to diffuse involvement and inflammation (i.e., the addition of lymphocytes and plasma cells); may be necrotizing
- Chronic lesions have variable fibrosis that may extend to the epidermis
- Overlying epidermis may be acanthotic or ulcerated
ADDITIONAL DIAGNOSTIC TESTS:
- Special stains for acid-fast bacteria and fungi to rule out an infectious cause
DIFFERENTIAL DIAGNOSIS (nodular skin lesions):
- Infectious panniculitis, especially Mycobacterium spp. and mycotic infections
- Juvenile sterile granulomatous dermatitis and lymphadenitis occurs exclusively in puppies (3-weeks to 4-months old); presence of periadnexal pyogranulomatous inflammation
- Cutaneous neoplasms
- Deep bacterial folliculitis and furunculosis
- Foreign body reactions
- Reactive histiocytosis (histiocytic infiltrates often centered around vessels)
- Sterile pyogranuloma syndrome
- Vaccine-associated granuloma
- Less commonly reported in horses and cats
- Lesions in horses typically found on the neck, thorax, abdomen, proximal limbs
- Ginn PE, Mansell JEKL, Rakich PM: Skin and appendages. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 5th ed. Philadelphia, PA: Elsevier Saunders; 2007:745-746.
- Gross TL, Ihrke PJ, Walder EJ, et. al. Diseases of the panniculus. In: Gross TL, Ihrke PJ, Walder EJ,, eds. Skin Diseases of the Dog and Cat. 2nd ed. Ames, IA: Blackwell Science Ltd; 2005:548-551.
- Hargis AM, Ginn, PE. The integument. In: Zachary JF, McGavin MD, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Elsevier Mosby; 2012:998,1075, 1077.
- O’Kell AL, Inteeworn N, Diaz SF, et. al. Canine sterile nodular panniculitis: A retrospective study of 14 Cases. J Vet Intern Med. 2010;24(2):278-284.
- Tham HL, Linder KE, Tucker A, Maggi R, Bizikova P. Protozoal nodular dermatitis and panniculitis in a rottweiler puppy caused by Caryospora biogenetic. Vet Dermatol. 2016;27(1):44-e12.
- Contreary CL, Outerbridge CA, Affolter VK, Kass PH, White SD. Canine sterile nodular panniculitis: A retrospective study of 39 dogs. Vet Dermatol. 2015;26(6):451-8.
- Rossi MA, Balakrishnan N, Linder KE, Messa JB, Breitschwerdt EB. Concurrent Bartonella henselae infection in a dog with panniculitis and owner with ulcerated nodular skin lesions. Vet Dermatol. 2015;26(1):60-3.