Skin diseases of old cats (Proceedings)

As cats age, they are predisposed to skin diseases and changes in the hair coat as a result of age and development of other medical problems. This seminar will discuss the most common and noteworthy skin diseases of older cats. The goal of the seminar to bring attention to changes that can affect the quality of life of the cat and alert the participant to skin diseases which are a sign of systemic disease.  Diagnosis, in general, is made via core diagnostic tests and/or skin biopsy in association with the cat's history and signalment. In contrast to young cats with skin disease, skin diseases in older cats, especially if acute in onset, warrant more advanced diagnostic tests (i.e. laboratory tests, imaging, skin biopsy) on first presentation.

“Unkempt hair coat” is the most global of all clinical signs that the cat has a medical condition that is preventing it from grooming.  Cats, in general, are considered fastidious groomers but it is important to ask the client if the hair coat changes are a recent development or not. Although rare, there are cats that owner report as not being “good groomers”.  Unkempt coats are characterized by, but not limited to, any combination of the following: increased oiliness, matting of tufts of hair, matting of large areas of the hair coat, scaling, odour, urine or faecal material on the coat, lip fold pyoderma, increased nail bed debris, scaling, bacterial pyoderma and/or Malassezia overgrowth.  The most common causes of an unkempt hair coat are related to mobility. The cat may have become obese preventing it from grooming or, and more likely, arthritic changes prevent the cat from grooming.  Any systemic disease that affects the cats overall feeling of wellness will be reflected in decreased grooming behaviour. These diseases include, but are not limited to, endocrine diseases (diabetes mellitus, hyperthyroidism, hyperadrenocorticism), renal disease, cardiac disease, neoplasia etc.

Unkempt hair coats may also develop in cats that are reported by owners to be “good groomers”. In these cases, the most likely cause is nutrition. The skin is a very large organ and utilizes large amounts of nutrients to maintain hair, sebum production, skin integrity, and skin immune system to mention the largest demands. In these cats, a thorough search for an underlying medical disease is warranted and is one of the times when routine laboratory work for geriatric cats can be invaluable.

Excessive scaling as a “new” occurrence warrants careful investigation. In homes where an older cat lives, owners often will add a new younger cat in anticipation of the loss of the elderly cat. The introduction of a new cat, from whatever sources, introduces risk for contagious skin disease, most notably parasitic diseases (e.g. fleas, Cheyletiella, and Demodex gatoi) and dermatophytosis. These diseases can be readily diagnosed using core diagnostic tests assuming suspicion is high. For a variety of reasons, clients owning older cats (especially indoor cats) will forego routine flea control and fail to mention this during the visit.

Excessive scaling is common in many cats with renal disease, hepatic disease, and intestinal neoplasia. It can also be the major clinical sign in immune mediated diseases. Pemphigus foliaceus is characterized by excessive scaling (see notes on facial dermatitis).  This disease can develop gradually as it waxes and wanes or quite acutely. A unique disease of notes is is generalized exfoliative dermatitis. This disease affects middle age to older cats and is characterized by widespread adherent scaling. It usually is first noted on the face and head but may start anywhere. Hair loss and development of concurrent microbial overgrowth, particularly Malassezia is common.

This clinical presentation is most commonly associated with thymomas and surgical removal may be curative. Excessive scaling (focal or widespread) can occur in other neoplastic diseases (e.g. epitheliotropic lymphoma).

Easily torn skin is a rare dermatological finding. The most common differential diagnoses are cutaneous asthenia and feline hypercortisolemia. The former is a disease of young cats and is readily apparent long before the cat becomes elderly. The most common cause of acquired skin fragility is feline hypercortisolemia.  This can be iatrogenic and has been observed to occur in cats with excessive exogenous glucocorticoid administration. These cats are not easily missed as they generally have a known medical condition necessitating steroid administration. Elderly cats that are protein deficient due to medical diseases usually present with thin skin that is not excessively fragile.  Older cats presenting with easily torn skin are highly suspect for hyperadrenocorticism often with concurrent diabetes mellitus.

Unilateral otitis externa/media with or without vestibular signs is most compatible with an ear tumour. In most cases, cats with ear tumours are presented for examination because of unilateral otitis externa/media and/or because of vestibular signs. In a cat with no prior history of ear disease, the finding of unilateral otitis externa/media with or without vestibular signs warrants an aggressive initial work up that includes imaging of the ear canal and bulla.  These cases are treated surgically and the more expedient the diagnosis the sooner treatment options can be pursued.

Pruritus that develops in an older cat could be due to an easily explainable aetiology (fleas) or be clinical signs of systemic disease. Exposure to fleas and contagious parasites are likely to be due to exposure to younger cat, change in flea control in the home, or change in the cat's living environment. More worrisome is the finding of demodicosis (D. gatoi or D. cati) on skin scraping from an older cat. As is the case in dogs, the finding of this parasite in an older cat is usually associated with the presence of a systemic disease. The most common conditions are diabetes mellitus and neoplasia. If bacterial and/or Malassezia overgrowth is identified on skin cytology this too is worrisome and warrants a medical investigation. It is worth noting that the feline demodicosis or microbial over growth may be limited to ears and pruritic otitis externa may be the presenting signs.

Acquired alopecia in older cats can occur for many reasons (see above), however one of the most important clinical signs to recognize is feline paraneoplastic syndrome.  This is a cutaneous manifestation of systemic disease. It is a unique alopecia that occurs in older cats with underlying malignancy, most commonly adenocarcinoma. There is an acute onset of widespread alopecia. A unique feature of the skin is that it is shiny in appearance and remaining hairs easily epilate. The skin is thin but not fragile. It can be associated with overgrowth of bacteria and Malassezia. Footpads may be painful, dry and fissured.

Ulcerative skin lesions in white cats should be aggressively evaluated as squamous cell carcinoma is a disease of middle age to older cats.  This is diagnosed by skin biopsy.