JPC SYSTEMIC PATHOLOGY
INTEGUMENTARY SYSTEM
September 2022
I-M14
Signalment (JPC #1802990): Young gilt
HISTORY: None
HISTOPATHOLOGIC DESCRIPTION: Haired skin and subcutis: Diffusely, the epidermis is thickened up to 5 mm with anastomosing psoriasiform rete ridges, acanthosis, intercellular edema (spongiosis), intracellular edema, and moderate parakeratotic and orthokeratotic hyperkeratosis. There are multiple, variably sized, up to 500µm X 100µm, intracorneal and intraepidermal pustules composed of many degenerate neutrophils and fewer eosinophils admixed with variable amounts of proteinaceous fluid and eosinophilic cellular and karyorrhectic debris. Within the superficial dermis, often perivascularly, there are many neutrophils and eosinophils with fewer macrophages and lymphocytes which often transmigrate the epidermis (exocytosis). There are mildly increased numbers of reactive fibroblasts and mild fibrosis within the dermis. The dermis is expanded by increased clear space, and lymphatics are often ectatic (edema). Blood vessels within affected areas are lined by mildly hypertrophied (reactive) endothelial cells. Low numbers of lymphocytes and plasma cells multifocally infiltrate the deep dermis and panniculus. Multifocally, apocrine glands are mildly ectatic.
MORPHOLOGIC DIAGNOSIS: Haired skin: Dermatitis, eosinophilic and neutrophilic, superficial, diffuse, moderate, with marked psoriasiform epidermal hyperplasia, intracorneal and intraepidermal pustules, and moderate parakeratotic-predominant hyperkeratosis, breed not specified, porcine.
CONDITION: Porcine juvenile pustular psoriasiform dermatitis
SYNONYMS: Pityriasis rosea, pseudo-ringworm
GENERAL DISCUSSION:
- A noncontagious, self-limiting, usually asymptomatic, symmetric, erythematous, maculopapular dermatitis that primarily affects suckling and young pigs (3-14 weeks old)
- Predilection for white breeds, especially Landrace
- One or more members of a litter may be affected
- Usually resolves spontaneously in 4 weeks
- Secondary bacterial infections with Staphylococcus hyicus are possible
PATHOGENESIS:
- Unknown etiology but possible hereditary component
- Attempts to transmit the disease or demonstrate an infectious agent have been unsuccessful
TYPICAL CLINICAL FINDINGS:
- Skin lesions are occasionally preceded by anorexia, vomiting, and diarrhea
- Hair loss does not occur and little pruritus is seen
TYPICAL GROSS FINDINGS:
- Symmetric, sharply defined, round, red, raised papules and plaques
- Lesions begin on the ventral abdomen, groin, or medial thighs then expand centrifugally, forming scaly plaques at the center
- Papules heal from the center outward; this produces rings with a center of normal skin surrounded by a zone of elevated erythematous skin and scales; rings coalesce forming mosaic or serpiginous patterns
- Occasionally lesions progress, affecting the lateral and dorsal aspects of the body
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Early: Superficial lesions composed of deep perivascular neutrophilic, eosinophilic, and mixed mononuclear dermatitis; +/- spongiosis and intraepidermal eosinophilic and neutrophilic pustules; superficial epidermal necrosis
- Late/healing: Marked psoriasiform epidermal hyperplasia (approximately evenly thickened epidermis with evenly elongated rete ridges that are clubbed, fused, or both at their bases); parakeratotic-predominant cellular crust
- Secondary bacterial infections are rare
ADDITIONAL DIAGNOSTIC TESTS:
- None; diagnosis is based on history, physical examination, biopsy, and elimination of other diseases
DIFFERENTIAL DIAGNOSIS:
For gross and histologic lesions:
- Dermatophytosis (I-F11; Microsporum nanum, Trichophyton mentagrophytes): Lesions occur anywhere on body, but usually not on ventral abdomen; hyphae and arthrospores within hair follicles
- Swinepox (suipoxvirus): Macules, papules, pustules, or crusts often generalized; ballooning degeneration and eosinophilic intracytoplasmic inclusion bodies
- Exudative epidermitis (greasy pig disease) (Staphylococcus hyicus): Exudative lesions start on head often becoming generalized; superficial suppurative folliculitis with cocci; rule out based on culture
- Dermatosis vegetans: Inherited disorder of young pigs; lesions are either present at birth or develop within first 3-weeks; fatal
- Erythematous maculopapular dermatitis progressing to thick, papillomatous crusts surrounded by a hyperemic raised border around a depressed center filled with brown-black, granular, brittle material; eventually become dark brown-black; prominent irregular epidermal hyperplasia
- May also have lesions on the coronary band and hoof (hoof malformation) which, if they occur, will be present at birth
- Concurrent giant cell pneumonia
COMPARATIVE PATHOLOGY:
- Psoriasiform dermatitis of young goats (pygmy and alpine) on the face, pinnae, neck, ventrum, and distal limbs; nonpruritic with areas of erythema, crusting, and alopecia; marked orthokeratotic and parakeratotic hyperkeratosis, epidermal hyperplasia, and neutrophilic microabscesses within the epidermis
- Psoriasiform dermatitis has been reported in macaques with lesions resembling those in humans (parakeratosis, rete ridge formation, microabscesses, suprapapillary epidermal thinning, epidermal inflammation, and reduction of the stratum granulosum.)
References:
- Cameron R. Integumentary system: Skin, Hoof, and Claw. In: Zimmerman JJ, Karriker LA, Ramirez A, eds. Diseases of Swine. 10th ed. Ames, IA: John Wiley & Sons, Inc; 2012: 261.
- Kramer JA, Bielitzki J. Integumentary system diseases of nonhuman primates. In: Abee CR, Mansfield K, Tardif S, Morris T. Nonhuman Primates in Biomedical Research Volume 2: Diseases. 2nd ed. London, UK: Academic Press; 2012:578.
- Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016: 546-7, 625, 630-2, 651, 698.
- Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1232-1233.
