Pathology in Practice

Jeremy R. Tobias 1Idexx Laboratories Inc, 1 Idexx Dr, Westbrook, ME 04092.

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James R. Steed 2Jackson Animal Clinic, 2281 N Highland Ave, Jackson, TN 38305.

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Frane Banovic 3Department of Small Animal Medicine & Surgery, College of Veterinary Medicine, University of Georgia, Athens, GA 30602.

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History

An approximately 2-year-old 2.93-kg (6.45-lb) spayed female domestic shorthair cat was evaluated because of bleeding, crusting, and alopecic lesions of the ears and face of 2 weeks’ duration. The cat was administered a single injection of methylprednisolonea (6.83 mg/kg [3.1 mg/lb], IM) and reexamined 1 month later. At that time, lesions had worsened with marked pruritus indicated by self-trauma (scratching and chewing of the skin) as well as involvement of paw pads, nail beds, and pressure points. Weight loss of 0.57 kg (1.25 lb; 19.4% of body weight) was evident. Prior medical history included ovariohysterectomy and routine vaccination at 8 months of age.

Clinical and Gross Findings

Physical examination revealed marked symmetric alopecia primarily affecting the head with associated crusting, hyperkeratosis, and mild ulceration. The lesion extended from the dorsal aspect of the head to the dorsal portion of the nasal planum; the margins and convex aspects of the pinnae were most severely affected. The concave aspects of the pinnae were predominantly spared (Figure 1). Similar lesions involving the nail beds, paw pads, and pressure points were evident.

Figure 1—
Figure 1—

Photographs of the head (A) and left ear (B) of an approximately 2-year-old domestic shorthair cat with alopecia, crusting, and hyperkeratosis extending from the pinnae to the dorsal aspect of the nasal planum. In panel A, the white suture caudal to the right ear indicates a site of punch biopsy. The margins and convex aspects of the pinnae are most severely affected with relative sparing of the concave aspects. Nail beds, paw pads, and pressure points are also affected (not shown).

Citation: Journal of the American Veterinary Medical Association 254, 10; 10.2460/javma.254.10.1163

Formulate differential diagnoses from the history, clinical findings, and Figure 1—then turn the page

Histopathologic Findings

Five full-thickness, 3-mm skin punch biopsy specimens were obtained from representative lesions of the head, axilla, inguinal and dorsal lumbar areas, and sternum. Histologically, all specimens had similar characteristics of lesion development; the epidermis had marked, diffuse, irregular hyperplasia (acanthosis) with severe overlying orthokeratotic and mild parakeratotic hyperkeratosis. The expanded stratum corneum contained numerous, vertically oriented, approximately 200-μm-wide burrows containing mites (Figure 2). In cross-sectional profiles, the mites measured 170 μm in the widest dimension and were ovoid with jointed appendages. Mites had a deeply striated, eosinophilic to yellow, chitinous exoskeleton with internal skeletal muscle, hemocoel, and reproductive organs (Figure 3). Colonies of bacterial cocci were admixed within the stratum corneum. Within the superficial dermis, there was a mild, perivascular to interstitial inflammatory infiltrate of eosinophils with increased numbers of perivascular mast cells and fewer lymphocytes and plasma cells.

Figure 2—
Figure 2—

Photomicrograph of a section of a skin biopsy specimen obtained from the cat in Figure 1. The epidermis has marked hyperplasia and hyperkeratosis with numerous mites present within vertically oriented burrows in the expanded stratum corneum. One mite is visible deep at the level of follicular ostia (arrowhead). The dermis has evidence of mild perivascular-interstitial eosinophilic inflammation (arrow). H&E stain; bar = 200 μm.

Citation: Journal of the American Veterinary Medical Association 254, 10; 10.2460/javma.254.10.1163

Figure 3—
Figure 3—

Photomicrograph of a representative mite in a section of a skin biopsy specimen obtained from the cat in Figure 1. Mites are ovoid and up to 170 μm in their widest dimension with a striated eosinophilic to yellow, chitinous exoskeleton and jointed appendages (arrow). Internally, skeletal muscle (arrowheads) surrounds the hemocoel and reproductive organs. H&E stain; bar = 50 μm.

Citation: Journal of the American Veterinary Medical Association 254, 10; 10.2460/javma.254.10.1163

Morphologic Diagnosis and Case Summary

Morphologic diagnosis: marked, diffuse, epidermal hyperplasia and hyperkeratosis with mild superficial perivascular-interstitial eosinophilic dermatitis and intracorneal burrowing mites (consistent with Notoedres cati).

Case summary: generalized notoedric acariasis (notoedriasis) in a cat.

Comments

For the cat of the present report, the markedly pruritic, hyperkeratotic plaques that primarily affected the margins and convex aspects of the pinnae and the microscopic identification of numerous, characteristic burrowing mites led to the diagnosis of notoedric acariasis (which in cats is also known as feline scabies). The pressure point and digital involvement supported the generalized anatomic distribution of this typically rare disease of North American domestic cats.

Prior to the discovery of mites in the case described in the present report, differential diagnoses for pruritic conditions focused on the head and pinnae included pemphigus foliaceus and hypersensitivity conditions (atopic or allergic diseases). With respect to other ectoparasitic infestations that could have caused similar lesions, Sarcoptes scabiei was considered most likely. The clinical distribution of lesions along the margins and convex aspects of the pinnae as well as the intracorneal burrowing may also be seen with infestation with sarcoptid mites. Compared with Notoedres spp, S scabiei have larger cross-sectional dimensions (up to 400 μm in width).1,2 Infestation with S scabiei is rare in cats,1 and the mites are typically only present in low numbers.1,2 Infestation with fleas, lice, Otodectes cynotis, Cheyletiella blakei, Lynxacarus radovskyi, or nonpathogenic free-living mites was considered unlikely because those are surface-dwelling rather than burrowing organisms.3,4 Infestation with Demodex spp was ruled out because those mites have an elongated profile.3

For cats with gross lesions similar to those of the cat of the present report, minimally invasive testing for mites should be performed prior to pursuing skin biopsy specimens. Methods of minimally invasive testing include collection of skin scrapings or acetate tape impressions of affected skin, fecal flotation (to detect mites ingested during grooming), and administration of empirical treatment.1–3 The number of mites detected in skin scrapings and acetate tape impressions of affected skin areas generally correlates highly with a patient's mite load2; such tests would have been expected to yield positive results in the case described in the present report had they been performed. Less invasive initial testing was not performed in the case described in the present report on the basis of the pet owner's preference. When examination of skin scrapings and acetate tape impressions of affected skin areas yield negative results, collection of skin biopsy specimens for histologic examination should be pursued. It is recommended that biopsy specimens are collected from multiple sites, including sites of severe crusting, to maximize the odds of capturing mites in tissue sections. Unless the pinnae are the only sites affected, pinna margins should not be biopsied because of the potential for scarring.1

Most notoedric mite species within the family Sarcoptidae predominantly infest bats. However, small mammals including felids, rodents, procyonids, and other insectivores are also reported hosts. Notoedres cati has nearly worldwide distribution and is the “best-studied… and only known zoonotic species”.5 These burrowing mites undergo their entire life cycle in the host's skin; although they cannot survive off the host (unlike Sarcoptes spp), notoedric mites may temporarily climb out of their burrows, thereby allowing for transmission of the highly contagious organisms.5

In cats, notoedriasis is associated with intense pruritus and erythematous papules that quickly develop into thick crusts accompanied by self-excoriation, progressive alopecia, and, in chronic cases, lichenification. The pinnae margins are typically affected first with subsequent involvement of the convex aspects of the pinna, face, and neck and potentially development of generalized disease.1 In addition, infestation may lead to secondary bacterial infection, leukocytosis, lymphadenopathy, emaciation, and ultimately death. Cats that develop fatal disease are more likely to be young or immunosuppressed. Even with successful medical treatment, the initial disease does not provide long-lasting immunity.5

The classic histopathologic features of notoedriasis in cats include robust orthokeratotic and parakeratotic hyperkeratosis with parakeratotic spires and acanthosis and spongiosis of the underlying epidermis. In contrast to the usual paucity of S scabiei organisms in the skin of affected cats, N cati mites are typically readily apparent within burrows through the stratum corneum. The morphology of mites in the case described in the present report was typical of N cati. The dermis of infested cats has a mild to moderate, eosinophil-rich, superficial perivascular to diffuse inflammatory infiltrate.1 In the cat of the present report, the degree of underlying dermatitis observed may have been reduced as a result of the prior corticosteroid administration.

Although N cati is relatively host specific, these organisms pose a zoonotic risk. In a reported case series from India,6 30 of 48 humans in contact with N cati–infested cats developed clinical signs of notoedriasis. Lesions described included “hyperemia and papulovesicular eruptions without any evidence of parasitic burrows,” excoriation, eczematous lesions, and pruritis. The hands and legs or the hands, legs, and face were the most frequent lesion distributions. The interdigital webs and genitalia were unaffected, which was noted to be a distinguishing factor from human scabies. In the affected humans, pruritus developed within hours after exposure to N cati–infested cats, and disease resolved without treatment 2 to 3 weeks following separation of individuals from the cats.6 In the cat of the present report, neither the owner nor other animals in the household developed clinical signs of notoedriasis.

The cat of the present report underwent treatment with topical application of selamectinb (15.39 mg/kg [7 mg/lb]) to the dorsal cervical region, which was repeated 14, 28, and 56 days later. Follow-up examination on day 35 revealed nearly complete resolution of all skin lesions as well as return of the lost body weight.

Footnotes

a.

Depo Medrol, Zoetis, Kalamazoo, Mich.

b.

Revolution, Zoetis, Kalamazoo, Mich.

References

  • 1. Gross TL, Ihrke PJ, Walder EJ, et al. Perivascular diseases of the dermis. In: Skin diseases of the dog and cat: clinical and histopathologic diagnosis. 2nd ed. Oxford, England: Blackwell Science, 2005;216220.

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  • 2. Sampaio KO, de Oliveira LM, Burmann PM, et al. Acetate tape impression test for diagnosis of notoedric mange in cats. J Feline Med Surg 2017;19:702705.

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  • 3. Milley C, Dryden M, Rosenkrantz W, et al. Comparison of parasitic mite retrieval methods in a population of community cats. J Feline Med Surg 2017;19:657664.

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  • 4. Ketzis JK, Dundas J, Shell LG. Lynxacarus radovskyi mites in feral cats: a study of diagnostic methods, preferential body locations, co-infestations and prevalence. Vet Dermatol 2016;27:425427.

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  • 5. Foley J, Serieys LE, Stephenson N, et al. A synthetic review of Notoedres species mites and mange. Parasitology 2016;143:18471861.

  • 6. Chakrabarti A. Human notoedric scabies from contact with cats infested with Notoedres cati. Int J Dermatol 1986;25:646648.

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