JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

November 2022

I-P08

 

Signalment (JPC# 1754374):  A stray cat

 

HISTORY:  This cat had severe dermatitis of the ears, face, and forelegs.

 

HISTOPATHOLOGIC DESCRIPTION: Haired skin, pinna: Approximately 80 percent of the stratum corneum is expanded by an up to 5 mm thick layer of parakeratotic hyperkeratosis within which are numerous 300µm wide tunnels that contain many cross and tangential sections of arthropods that are 250 x 150µm diameter and have a 4µm thick chitinous exoskeleton, dorsal spines, a hemocoele, striated muscle, jointed appendages, and digestive and reproductive organs. There are rare, 60µm diameter eggs with a 5µm thick, tan, anisotropic shell that contain basophilic globular material. There are multifocal intracorneal pustules that contain degenerate neutrophils and necrotic debris. Diffusely, the superficial dermis is infiltrated by moderate numbers of perivascular and to a lesser extent periadnexal neutrophils, macrophages, eosinophils, fewer lymphocytes, and plasma cells. The epidermis is moderately hyperplastic characterized by deep, anastomosing rete ridges and acanthosis, and there is increased intracellular clear space (edema) and prominent intracellular bridging (spongiosis).  Apocrine glands are frequently dilated and lined by attenuated epithelium.      

 

MORPHOLOGIC DIAGNOSIS:  Haired skin, pinna: Parakeratosis, diffuse, severe, , chronic with intracorneal pustules, neutrophilic and histiocytic perivascular dermatitis, and intracorneal arthropods and eggs, breed not specified, feline. 

 

ETIOLOGIC DIAGNOSIS:  Epidermal notoedriasis or epidermal notoedric acariasis

 

CAUSE:  Notoedres cati

 

CONDITION:  Notoedric mange

 

CONDITION SYNONYMS:  Feline scabies, head mange

 

GENERAL DISCUSSION: 

• Uncommon to rare disease primarily of cats (feral cat populations) and rabbits, but also affects foxes, dogs, wild felids, hamsters, raccoons, coatis, and humans
• Highly contagious, intensely pruritic, transmissible skin disease 
• Family Sarcoptidae; the Notoedres cati mite has a life cycle similar to S. scabei
• Lesions in the cat begin on the head and ears, particularly on the margin of the pinna, and may extend to the neck and feet; may cause a regional lymphadenopathy

Lesions in the dog are indistinguishable from sarcoptic mange

 

LIFE CYCLE:

• Obligate parasites that survive off of the host for only a few days
• Completes life cycle within the stratum corneum
• Female burrows through the horny layer of the epidermis between follicles, laying eggs in a tunnel
• Larvae hatch from eggs and burrow to the surface of the skin
• Larvae mature in the molting pocket

 

PATHOGENESIS:

• Mite burrows in the stratum corneum, eliciting hyperkeratosis 
• Complex hypersensitivity reaction similar to canine sarcoptic acariasis is suspected
• Highly contagious, transmitted by direct contact

 

CLINICAL FINDINGS:

• Intense pruritis
• Lesions first appear at medial edge of pinna, and spread to the face, eyelids, neck, feet, and perineum; can become generalized
• Peripheral lymphadenopathy

 

GROSS FINDINGS:

• Begins as a erythematous papular rash that progresses to partial alopecia, thickening and wrinkling of the skin (lichenification) with yellowish-gray crusts
• Excoriations and secondary infection are common
• Peripheral lymphadenopathy

 

LIGHT MICROSCOPIC FINDINGS:

• Hyperplastic, eosinophil-rich, superficial perivascular dermatitis with focal parakeratosis in mounds or caps with mites embedded within tunnels
• Moderate acanthosis with mild spongiosis
• Mites: 
  • Oval; up to 250x150µm; medium-length, un-jointed, sucker-bearing extensions off jointed appendages (difficult to see in histologic section); dorsally located anus (difficult to see in histologic section)
  • Arthropods usually have some or all of the following features: Chitinized exoskeleton, striated muscles, tracheal ring and jointed appendages with suckers
• With no arthropods present, resembles other allergic skin diseases

 

ADDITIONAL DIAGNOSTIC TESTS:

• Diagnosis is based on history, clinical signs, and demonstration of the mites in section
• Skin scraping:  Mites are usually numerous, but cats with allergic disease may have only a few mites present
• Fecal flotation for ingested mites and eggs

 

DIFFERENTIAL DIAGNOSIS:

Histologic

Acariasis

• Sarcoptes scabiei var. canis (I-P06):  Larger mite (300-600µm x 250-400µm) with longer dorsal spines and a terminal anus (Notoedres cati has a dorsal anus); rarely causes disease in cats; not commonly seen because of the small number of mites in the stratum corneum
• Otodectes cyanotis:  Lesions are primarily in the external ear canal; does not burrow within the stratum corneum
• Demodicosis (I-P07, rare in cats):  
  • Demodex cati:  Elongated, slender, "cigar shaped", and intrafollicular; may also live in the sebaceous gland
  • Demodex gatoi:  Shorter, primarily inhabits the stratum corneum
  • As yet unnamed species:  Resembles D. gatoi, but large
• Cheyletiella blakei:  Mites are large (350-500µm) and elongate, legs bear cones instead of claws, have a cone-shaped sensory organ, and don't burrow but live in the keratin layer

Facial dermatitis

• Feline allergic miliary dermatitis:  Caused by food allergy and atopy; histologic lesions may be identical aside from the presence of the mite; dermal inflammation of food allergy often more severe and deeply extensive
• Feline Herpesvirus-1 associated dermatitis: Caused by reactivation of the alphaherpesvirus from the trigeminal ganglion, not present with respiratory disease but may follow it; ulcerative and necrotizing eosinophilic dermatitis

Gross 

Other intensely pruritic skin diseases with predilection for face and ears:

• Otodectic acariasis
• Food allergy
• Pemphigus foliaceous
• Atopic dermatitis

 

COMPARATIVE PATHOLOGY:

• Notoedres muris causes mange in rats (and guinea pigs due to interspecies contact) with lesions primarily on the ears, but also on the nose, tail and external genitalia (hairless skin)
• Notoedres notoedres causes mange in hamsters with lesions on the ears, nose, feet, and perianal areas; Notoedres cati can also infest colonies of hamsters
• Notoedres cati in rabbits, similar appearance and distribution as Sarcoptes
• Notoedres spp. are common in squirrels; similar appearance as described
• Civets: Notoedres sp. Causes severe alopeciaand crusting with acanthosis, hyperkeratosis and intralesional mites

 

References:

1. Barthold SW, Griffey SM, Percy DH. . Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing Professional; 2016:154,191,238,303.
2. Church ME, Terio KA, Keel MK. Procyonidae, viverridae, hyenidae, herpestidae, eupleridate, and prionodontidae. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018:316.
3. Delaney MA, Treuting PM, Rothenburger JL. Rodentia. In: Terio KA, McAloose D, St. Leger J, eds. Pathology of Wildlife and Zoo Animals. Cambridge, MA: Elsevier; 2018:513
4. Maudlin E, 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; 2016:675.
5. Welle MM, Linder KE. The Integument. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1182.

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