Skin diseases in kittens

Introduction

Skin conditions in kittens are uncommon, but their presence may cause distress for owners and breeders. This article aims to introduce feline pediatric dermatology to aid practitioners when presented with a kitten that has a skin problem. The article will concentrate on the more common conditions, and treatment will be mentioned only briefly – options may be limited due to the age of the patient, as not all products may be licensed or suitable for young animals (and indeed may even be toxic). Congenital and hereditary conditions should be considered in newborn kittens and within the first weeks of life 1. Husbandry and nutrition should be reviewed, especially if several kittens in a litter are affected (Figure 1). Infections may be transmitted to young kittens by the queen or other animals in the household, especially if there is access to outdoors. In an older kitten that is allowed to roam freely outside, a wider range of potential acquired causes become possible, and the geographical prevalence of infectious agents should be a factor when evaluating differentials. Immune-mediated and hypersensitivity disorders typically have a later onset, but can start at a relatively young age 2.

Congenital and hereditary conditions

Congenital and genetic skin problems typically manifest at an early age. Genodermatoses, defined as genetic diseases that are expressed as skin conditions, can affect the epidermis, the dermoepidermal junction, the hair follicle, the hair shafts, the dermis and/or pigmentation. Most are rare, and many are limited to single case reports (Table 1) 1. Most generally have no effective therapies, however diagnosis is needed for an individual prognosis and genetic counseling 1. Examples include keratinization defects, which may be localized, as in the Bengal breed (Figure 2), or generalized, as in primary seborrhea. Genetic dermo-epidermal diseases cause vesicles, erosions and ulcers. Defects of collagen synthesis are known as Ehlers-Danlos syndrome (Figure 3). Congenital pigment abnormalities may be cosmetic, as in acromelanism, or debilitating, as in Chediak-Higashi syndrome. Hypotrichosis or alopecia, whilst sometimes regarded as desirable breed characteristics, can also be the result of rare genodermatoses, and some are associated with a fatal outcome. 

Table 1. Examples of reported genodermatoses in young cats (from 1).

Infectious skin diseases

Infectious skin disease may affect young animals, partially due to their immature immune systems. These diseases can be viral, bacterial, fungal, ectoparasitic, or protozoal in nature. 

Viral dermatoses

Several viral infections may cause dermatological lesions (Table 2); such conditions are more typically seen in adult cats, although infection often occurs at a young age 6. 

Feline calicivirus (FCV) is one of the most prevalent causes of upper respiratory tract diseases in cats worldwide. Infected and subclinical carrier cats are the most common source of infection. Acute upper respiratory and ocular signs in kittens or young cats are usually seen, but a variety of other signs, including oral ulceration and a limping syndrome, are reported. Epizootic outbreaks of virulent systemic disease (VSD) with high mortality rates have been reported. VSD causes pyrexia, edema of the head and paws, epithelial necrosis, oral ulceration and occasionally jaundice, dyspnea and bleeding tendencies 6,7 (Figure 4). Such outbreaks usually occur in multi-cat environments, and have been reported in cats from 8 weeks to 16 years of age 7. Clinical diagnosis is supported by viral antigen identification by polymerase chain reaction (PCR) panels in mucosal swab samples. Therapy is supportive, available antivirals are not curative. Controversial results have been published concerning the protective effect of FCV vaccination against VSD 6,7.

Table 2. Skin signs associated with viral infections in cats (from 6).

Bacterial

Bacterial skin diseases in cats can be divided into superficial and deep dermatoses. Superficial infections, involving the epidermis and follicles, are usually secondary and commonly seen in association with hypersensitivities. The reported age of onset varies, reflecting the primary disease, with the youngest being six months of age. Lesions often reflect self-trauma due to pruritus, and consist of multifocal alopecia, crusts, excoriations, erosions and ulcerations. The most commonly affected sites are the face, neck, limbs and ventral abdomen 2,8.

Deep bacterial infections, involving the dermis and/or subcutaneous tissues, may be associated with traumatic implantation of environmental or commensal bacterial species. Deep nodular skin and subcutaneous lesions with ulcers and draining tracts may be caused by saprophytic bacteria such as Nocardia spp., although such infections are mostly seen in immunocompromised adult animals. Abscesses due to fight wounds are common in young adult outdoor cats 8. Necrotizing fasciitis is a potentially fatal deep infection and has been reported in an 8-week-old kitten 9.

Mycobacterial infections from a variety of causative agents can produce a range of clinical presentations, and have variable geographic distribution. Regardless of the causative species, most cases occur in adult cats with outdoor access, but in contrast, Mycobacterium lepraemurium tends to cause disease in young male cats 10.

Differential diagnoses of deep nodular skin and subcutaneous lesions include fungal or algal infections and neoplasia, and tissue samples for cytology, histopathology and microbiology are necessary for diagnosis. The zoonotic potential should be considered 8.

Fungal

Fungal skin diseases may be categorized as superficial (dermatophytosis, Malassezia dermatitis) intermediate (subcutaneous), and systemic (deep). Malassezia dermatitis is a complicating factor in many feline skin diseases, and carriage is common in breeds with genetic follicular dysplasia (Devon Rex, Cornish Rex and Sphynx) 11.

Dermatophytosis is a zoonotic superficial fungal infection of keratinized skin structures, with Microsporum canis being the most common cause in cats. Risk factors include young age, lifestyle and warm locations. The infective form of dermatophytes is the arthrospore, which can be transmitted by direct contact or fomites 11,12. Clinical signs include hair loss, papules, scales, crusts, erythema, follicular plugging, hyperpigmentation and onychodystrophy. Lesions are usually asymmetrical and occur most commonly on the face, although they may progress to other body areas. Pruritus is minimal to absent. Diagnosis can involve a number of complementary diagnostic tests, including Wood´s lamp examination (Figure 5), direct microscopic examination of hair and scales, dermatophyte culture, PCR and biopsies. Spontaneous resolution is likely in most immunocompetent hosts, but treatment is recommended to hasten resolution and to prevent spread to other animals and people. Oral and topical antifungals with environmental decontamination are typically used in combination.

Intermediate and deep mycotic infections can take a variety of forms. Sporothrix schenckii can cause a granulomatous, cutaneous or subcutaneous infection, with the development of nodules, ulcers and crusts. Intact outdoor male cats, involved in fights, are most commonly affected 11. In addition, traumatic implantation of fungi from the environment may lead to cutaneous and subcutaneous infections; hyalohyphomycosis is caused by nonpigmented molds that lead to pyogranulomatous inflammation (although the disease may disseminate), and phaeohyphomycetes are pigmented fungi that can cause dermal and subcutaneous nodules which may then ulcerate 11. It is also notable that Persian cats are predisposed to subcutaneous dermatophytic infections 11,12.

Deep mycotic infections are uncommon in cats, but outbreaks occur in endemic regions 12. The most common is cryptococcosis, with infection usually by inhalation. Clinical signs consist of upper respiratory signs, ocular, neurological and cutaneous lesions including papules, nodules and ulcers 11. Cryptococcus neoformans infection has recently been reported in a 3-month-old kitten with seizures 13.

Oomycetes are aquatic organisms closely related to algae, although the diseases they cause closely resemble fungal infection; a typical example is pythiosis, caused by Pythium insidiosum. The infective form can penetrate damaged skin and manifests mainly as cutaneous and subcutaneous lesions, although intestinal involvement is possible 11. Pythiosis has recently been reported in an eight-week-old kitten 14.

Parasites

Ectoparasitic skin diseases are common in cats, with the prevalence varying depending on the geographical area and the cat´s lifestyle 15. Conditions rarely seen in kittens are listed in Table 3, and treatment options will depend on available licensed products. The most relevant parasites are discussed here.

Table 3. Ectoparasites uncommonly seen in kittens (from 15).

Otodectic mange is caused by the mite Otodectes cynotis, transmitted primarily by direct contact. Juvenile cats are predisposed. Infection causes pruritic, erythematous and ceruminous otitis externa with large amounts of brown-black dry cerumen. Diagnosis is made by microscopic identification of the mite or its eggs 15.

Cheyletiellosis is contagious and zoonotic, with Cheyletiella blakei being adapted to the cat. The mite lives in the stratum corneum without burrowing. The disease occurs more commonly in young animals or immunocompromised adults. Most affected cats show exfoliative dermatitis affecting the dorsolumbar area and variable pruritus. The diagnosis is made by microscopic observation of the parasite or its eggs 15.

Demodicosis is uncommon to rare in the cat. Four species have been identified: Demodex cati, D. gatoi, D. murilegi and D. obliquus 16. D. gatoi lives in the stratum corneum and, in contrast to the others, is contagious. The most common clinical sign is pruritus, ranging from absent to severe. Diagnosis is confirmed by observation of the mite or eggs on superficial skin scrapings 15. One report gives the age of infected cats to vary between 4 months and 11 years 17.

Fleas are common ectoparasites in cats, but their prevalence varies with the geographical location. The species most frequently identified is Ctenocephalides felis felis 2. Flea-bite hypersensitivity may be the sole hypersensitivity in a cat, or may coexist with others. The clinical signs are similar to those in feline atopic skin syndrome (FASS) and include head and neck pruritus, excoriations, self-induced alopecia, eosinophilic granuloma complex and miliary dermatitis. Generalized or localized pruritus may be present 2. Diagnosis is based on the clinical presentation, the presence of fleas or flea feces, and response to flea control with adulticides and insect growth regulators. Intradermal skin tests and in vitro serologic tests may support the diagnosis, however, normal cats may have positive results 2.

Protozoa 

Leishmaniosis is increasingly reported in cats in endemic areas, with cutaneous nodules being the most common clinical sign; ulcers, scaling and alopecia are seen less commonly. In a recent review, the youngest affected cat was six months old 18, but middle-aged cats are more often affected. Diagnosis is made by cytology of fine-needle aspirates, biopsy, immunohistochemistry or PCR. The use of insect repellents for prevention against infection and for the control of the reservoir role should be used in endemic areas 18.

Cutaneous involvement in Toxoplasma gondii infection is uncommon in cats, although nodules and ulcers are reported in a few cases. A case of severe nodular skin infection with Caryospora bigenetica has been reported in a stray kitten (Figure 8) 19.

Hypersensitivity

Feline atopic skin syndrome (FASS)

This is a hypersensitivity disorder typically associated with environmental allergens. Cats may also have food allergy and/or asthma. The age of onset in the majority of cases is young, with reported mean ages from 6 months to 5 years. Abyssinian, Somali and Ocicat breeds seem predisposed. Clinical presentations are heterogeneous, and include miliary dermatitis, self-inflicted alopecia or hypotrichosis, head and neck pruritus and eosinophilic granuloma complex. FASS is a clinical diagnosis based on the presence of compatible clinical signs and exclusion of other diseases with similar clinical features, such as ectoparasites, infections and food allergy 2.

Food allergy 

Adverse food reactions include toxic and non-toxic, non-immunological and immune-mediated conditions, including food allergy. Food allergy may coexist with FASS or be the sole hypersensitivity in cats. Food allergy is clinically indistinguishable from FASS and an elimination diet is required for diagnosis. The age of onset varies between 3 months and 13 years in studies 2.

Ear disease 

Otitis externa in kittens is most commonly caused by ear mites, as discussed above 15,20. Although otitis externa is reported in 21% of cats with FASS, this is less often than in canine atopic dermatitis 2,20. Auditory tube dysfunction may contribute to middle ear effusion and inflammation. Viral upper respiratory tract infections may predispose cats to ascending bacterial middle ear infection via the auditory tube 21 (Figure 9).

Proliferative and necrotizing feline otitis externa (PNOE) is a rare disorder seen both in kittens and adult cats. Lesions are often bilateral and consist of well-demarcated proliferative dark-colored plaques and exudate at the base of the pinna, the opening of the ear canal and the vertical ear canal. The pathogenesis is unknown, but an immune-mediated disorder involving keratinocyte apoptosis is suspected. Systemic and topical treatment with corticosteroids and calcineurin inhibitors has been successful in most cases 20 (Figure 10).

Inflammatory aural polyps are benign nodules originating from the epithelium lining the middle ear, nasopharynx or the auditory tube. Polyps may be confined to the middle ear or may extend to the ear canal or nasopharynx. Signs of otitis externa, vestibular or respiratory signs, or Horner’s syndrome may be seen, and otitis media may develop 20,21. Polyps are most common in young cats and kittens, but can arise at any age. Besides otoscopy, diagnostic imaging is recommended for visualizing the extent of the polyp; definitive diagnosis requires histopathology. Polyps are usually treated by traction avulsion or ventral bulla osteotomy, although recurrence is common 20 (Figure 9).

Miscellaneous conditions

A variety of nutritional, environmental, psychogenic, immune-mediated and autoimmune skin diseases have been reported in kittens. Other than those included above, a few are noteworthy. Haircoat abnormalities with an early onset can have several etiologies besides genodermatoses (Table 1), including poor husbandry, nutrition or hygiene (Figure 1). Abnormal grooming behavior of the queen may lead to facial alopecia in kittens 22. Tyrosine deficiency in the diet leads to hypochromotrichia, which is manifested as a reddish-brown hair color in black cats 23. Diseases involving pruritic behavior such as feline maculopapular cutaneous mastocytosis 24, idiopathic neck ulcerative dermatitis, hypereosinophilic syndrome and perforating dermatitis are seen in cats of all ages, including the young 25.

Conclusion

Kittens and young cats may suffer from a variety of skin diseases, and a thorough history is an essential part of the diagnostic workup. When considering differentials, the clinician should take into account age of onset, whether others in the litter are affected, if there is possibility of contagion, and if the kitten or in-contact animals have access to the outdoors. Diagnostic tests are performed in accordance with the differentials, and may include samples for infectious agents, biopsies, allergy workup, or diagnostic imaging in addition to clinical judgement.