JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

October 2022

I-P04 (NP)

 

SIGNALMENT (JPC# 21474-19):  A 1-year-old dog

 

HISTORY:  This dog presented with mild alopecia and erythematous and edematous areas with papules and pustules involving the skin of the ventral trunk and extremities. The dog was housed under unsanitary conditions.

 

MICROSCOPIC DESCRIPTION:  Haired skin: Multifocally there are numerous eosinophils, degenerate neutrophils, lymphocytes, and plasma cells surrounding and occasionally infiltrating through the follicular epithelium into the lumen (perifolliculitis, transmural/luminal folliculitis) and adnexa. Inflammatory infiltrates are admixed with variable amounts of pale blue mucinous matrix and edema. Multifocally, hair follicles contain few cross and tangential sections of nematode larvae and rarely adults; nematodes are 20-40 µm wide and have a 3-5 µm thick, smooth, eosinophilic cuticle; platymyarian-meromyarian musculature; and a pseudocoelom that contains an intestine lined by uninucleate cuboidal cells. Adult nematodes also have a single uterus filled with eggs. Rarely, previously described rare larvae are present within mildly ectatic apocrine glands. Diffusely, previously described inflammation extends into the superficial dermis often surrounding an increased number of small caliber blood vessels lined by plump endothelial cells (telangiectasia). Diffusely, the epidermal and follicular epithelium is moderately hyperplastic with rete ridge formation, acanthosis, minimal spongiosis, and parakeratotic hyperkeratosis. There are rare areas of ulceration with an overlying serocellular crust as well as aggregates of viable and degenerate neutrophils within the remaining stratum corneum.  

 

MORPHOLOGIC DIAGNOSIS:  Haired skin: Dermatitis, perifolliculitis and folliculitis,  eosinophilic, multifocal, moderate, with follicular and epidermal hyperplasia, parakeratotic hyperkeratosis, and intrafollicular nematode larvae and adults, breed not specified, canine

 

ETIOLOGIC DIAGNOSIS:  Pelodera (rhabditic) dermatitis

 

CAUSE:  Pelodera strongyloides (formerly Rhabditis strongyloides)

 

GENERAL:  

• A free-living nematode of the order Rhabditida whose larva cause nonseasonal, pruritic dermatitis most often in dogs, occasionally in cattle; horses and sheep are rarely affected
• Lesions commonly occur in areas in contact with unsanitary, moist bedding (e.g. ventral trunk, feet, legs, perineum, tail)
• Life cycle is direct
• The free-living saprophytic adult nematode is found in longstanding, decaying organic debris, especially straw, rice hulls, or hay sorted in long term contact with the ground in damp conditions

 

PATHOGENESIS:  

• Moist, unsanitary conditions predispose to infection; larvae enter via broken skin
• Larvae invade hair follicles; acute eosinophilic dermatitis develops, commonly with suppurative folliculitis
• Pruritus can result in self-induced trauma that may lead to secondary bacterial infections
• Infection can spontaneously clear when the animal is removed from unsanitary conditions

 

TYPICAL CLINICAL FINDINGS:  

• Moderate to marked pruritus in most species (absent in cattle); localized alopecia; dermatitis of the ventral feet, legs, thorax and abdomen, perineum, and tail (areas in contact with unsanitary, moist bedding)
• Most reported cases have been in short-coated dogs

 

TYPICAL GROSS FINDINGS:  

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:  

• Eosinophilic and pyogranulomatous inflammation surrounding nematodes in the lumina of the hair follicles or dermis
• Eosinophilic and lymphoplasmacytic perivasculitis, perifolliculitis, folliculitis (often mural), and furunculosis, with hyperkeratosis and nematode segments
  1. Epidermal hyperplasia characterized by irregular acanthosis, hyperkeratosis
• Pelodera sp. has the following characteristics:  Smooth cuticle, small diameter, paired lateral alae (usually absent in tissue section), platymyarian-meromyarian musculature, rhabditiform esophagus (corpus, isthmus, bulb), uninucleate intestinal cells with a low microvilli border, reflexed ovaries with comparatively large ova
  1. The small size of the nematode may make many of these features difficult to discern in histologic sections

 

ADDITIONAL DIAGNOSTIC TESTS:  

• Deep skin scraping; trichogram (Capitan, Vet Dermatol 2017); biopsy
• Concentration of the nematode larvae from a bedding sample using the Baermann technique

 

DIFFERENTIAL DIAGNOSIS:  

• Grossly:
  1. Bacterial dermatitis 
  2. Contact dermatitis
  3. Demodicosis (I-P07):  Mites are 40x300 um with 2 rows of 6-8 legs; within follicular lumina and rarely in sebaceous glands
  4. Sarcoptic acariasis (I-P06):  Mites are 200-400 um in length; within stratum corneum
  5. Superficial bacterial folliculitis
  6. Dermatophytosis (I-F11)
• Microscopically:
  1. Hookworm dermatitis: lesions on areas of body in frequent contact with the ground, especially distal limbs, feet, interdigital areas; larval migration tracts may be seen histologically
  2. Dirofilariasis (C-P03)
  3. Strongyloidiasis
  4. Demodicosis (I-P07)

 

COMPARATIVE PATHOLOGY:  

• Horse:  Rare; marked alopecia; skin may be thickened and wrinkled with pustules on ventral abdomen and mammary gland; pruritus is variable
• Guinea pig:  Rare; dermatitis of the ventral thorax and abdomen; alopecia, crusting, erythema, and papules
• Sheep:  Rare; loss of wool, hyperkeratosis, lichenification
• Cattle:  Dermal pruritus can be absent; lesions become lichenified

 

REFERENCES:  

1. Capitan RGM, Noli C. Trichoscopic diagnosis of cutaneous Pelodera strongyloides infestation in a dog. Vet Dermatol. 2017;28(4):413-e100.
2. Gardiner CH, Poynton SL. An Atlas of Metazoan Parasites in Animal Tissues. Washington, DC:  Armed Forces Institute of Pathology; 2006:14-15.
3. Gross TL, Ihrke PJ, Walder WJ, Affolter VK. Skin Disease of the Dog and Cat, 2nd ed. Ames, IA: Blackwell Publishing; 2005:449-451. 
4. Mauldin EA, Peters-Kennedy J. Integumentary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals, Vol 1. 6th ed. Philadelphia, PA:  Elsevier; 2016:689. 
5. Welle MM and Linder KE. The Integument. In: Pathologic Basis of Veterinary Disease. 7^th ed. Ed. Zachary JF. St. Louis, MO: Elsevier; 2022:1238. 

 

 

 

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