A diagnostic approach to skin disease in geriatric cats

In an aging cat, acute onset of skin disease may be the first sign of an underlying systemic disease. The goal of this article is to help you formulate a diagnostic plan when a geriatric feline patient presents with adult-onset skin disease or changes to the coat. Based on the clinical presentation and clinical signs, possible differential diagnoses will be discussed as well as recommendations regarding the first- and second-line diagnostic tests. The diseases and differential diagnoses are grouped by the presenting complaint or predominant clinical sign. In an older cat with no history of skin disease or in a case in which a dramatic change to the skin or coat is the presenting complaint, more advanced or aggressive diagnostics are often warranted on first presentation.

It is imperative to start with a complete and detailed patient history. The history should include where and when the lesions first started, whether or not the cat is pruritic, a thorough medication history of both long-term and newly administered medications, any progression or changes in the clinical signs, and any observations about the cat's systemic health (e.g. drinking and urination habits, appetite, weight loss, activity).

It is also important to remember that even though more aggressive diagnostics may be indicated in an older feline patient, common diseases still occur commonly in older cats. For example, even an older cat can develop lesions secondary to flea hypersensitivity if there is a break in the administration of flea control products or a change in the cat's environment. Routine monthly flea preventive is recommended for all cats, regardless of their age.

CORE DIAGNOSTICS

Regardless of the initial presenting complaint, it is important to start the diagnostic investigation with these core dermatologic tests:

• Cytologic examination of skin and otic samples

• Superficial and deep skin scrapings

• A trichogram

• An otoscopic examination

• A Wood's lamp examination

• Examination of collected hair for adult fleas, flea feces, other ectoparasites, crust, or scale.

A dermatophyte culture is often warranted as a first-line diagnostic test in feline patients, especially if a cat is deemed to be at risk (e.g. indoor-outdoor lifestyle, new cat added to the household, interaction with other cats). Most of these tests can be performed during the initial examination. The results of these core diagnostics will directly affect treatment or recommendations for additional diagnostics.1

CLINICAL SIGNS

Unkempt hair coat

An unkempt hair coat is a generalized clinical sign that typically indicates a cat is not grooming itself as it normally would. It can be characterized by increased oiliness, matting or adhered tufts of hair, scales, odor, fecal or urine contamination of the coat, exudate accumulation, evidence of bacterial or yeast overgrowth on the skin, or paronychia.2

It is important to question the owner to try to establish when the signs of the unkempt coat started and how they progressed. Many causes of an unkempt coat are the result of a problem with a cat's mobility stemming from arthritis, lethargy, or obesity. If a cat is still reported to be grooming well and has a normal activity level, then inadequate nutrition or an endocrine disorder could be the underlying cause (Figure 1). Cardiac disease or neoplasia is another possible cause of decreased activity leading to decreased grooming.

1. Dermatophytosis, likely secondary to immunosuppression from gastrointestinal lymphoma and diabetes mellitus, was diagnosed in this cat with an unkempt coat.

Core diagnostic tests are certainly indicated to rule out parasites as well as to determine if bacterial or yeast infections are the primary cause or are complicating a definitive diagnosis. A complete blood count, serum chemistry profile, and urinalysis are indicated as first-line diagnostics to begin to rule in or rule out an endocrine or metabolic disorder (e.g. hyperthyroidism, hyperadrenocorticism, diabetes mellitus, renal disease).

Examination of the oral cavity and palpation of the thyroid gland can also help to make a complete differential diagnosis list. If the patient seems to be in pain or has mobility, joint, or gait abnormalities, a radiographic examination to check for arthritic or other bony changes should be considered.

It is important to discuss pain management strategies with the owner. This is not only in the form of medications but also can entail environmental changes, such as making sure that litter boxes are accessible and that the boxes do not have high walls or small openings where an arthritic cat would have trouble maneuvering.

Excessive scaling

Scale refers to flakes of keratin that break off from the cornified layer of the epidermis. Scaling as a new clinical sign should prompt a thorough investigation using core diagnostic tests.2 Dermatophytosis should also be ruled in or ruled out based on the results of a trichogram, Wood's lamp examination, and fungal culture. It is important to ask the owner whether any animals have been added to the household as well as about the use of flea control products. Deep and superficial skin scrapings are useful in determining whether Cheyletiella or Notoedres species infections are causes of scale. A fecal examination can also be helpful if certain contagious mites (i.e. Demodex gatoi) are suspected.3

If core diagnostics do not reveal the underlying cause, other differential diagnoses include immune-mediated skin diseases, such as pemphigus foliaceus or degenerative mucinous lymphocytic mural folliculitis. Immune-mediated diseases are diagnosed based on the results of a skin biopsy, which would be indicated in an older cat once both bacterial and fungal infections have been ruled out or treated.4

2. Large scales on the cranial dorsum of a cat with paraneoplastic exfoliative dermatitis secondary to thymoma. A skin biopsy site can be seen on the cat's neck.

Primary skin neoplasia (epitheliotrophic T cell lymphoma) or paraneoplastic exfoliative dermatitis can also present as excessive scaling with varying levels of pruritus (Figure 2). Scales are often large and broad, sometimes exfoliating in sheets. Other possibilities include drug eruption, erythema multiforme, and sebaceous adenitis. Skin biopsy can be diagnostic; however, because paraneoplastic exfoliative dermatitis is associated with thymoma, full blood work and thoracic radiographs are recommended if the skin biopsy comes back as consistent with paraneoplastic dermatitis or if biopsy results are nonspecific. Surgical removal of the thymoma can be curative in these cases.5,6

The treatment of and prognosis for diseases associated with scaling are quite variable, so determining a definitive diagnosis is important to be able to have an informative conversation with the owner.

Thin, fragile skin

Thin, fragile skin, sometimes called hyperfragility or feline fragile skin syndrome, is a rare dermatologic finding. It is characterized by very thin skin that leads to spontaneous nonhemorrhagic and nonpainful tearing (Figure 3). An underlying cause is not always found but should always be aggressively sought. Possible causes include spontaneous hyperadrenocorticism (rare), iatrogenic hyperadrenocorticism from excessive use of corticosteroids, diabetes mellitus, hepatic lipidosis, use of progestational drugs (megestrol acetate), a progesterone-secreting adrenal tumor,7 and cholangiocarcinoma.

3. A cat with a wound secondary to feline fragile skin syndrome. The dorsal neck is often affected because of self-trauma or handling or scruffing.

Cutaneous asthenia is another cause of fragile, easily torn skin, but it is a congenital disease of collagen or elastin and typically shows up in very young cats. However, severe metabolic disorders could exacerbate a subclinical case of cutaneous asthenia, causing the new clinical sign of hyperfragility in an older cat.8,9

Fragile skin syndrome is often diagnosed based on clinical signs alone, since the presenting signs are pathognomonic for the disorder. The search for the underlying cause includes a complete blood count, a serum chemistry profile, a urinalysis, and specific tests such as an ACTH stimulation test, a low-dose dexamethasone suppression test, or abdominal ultrasonography. Skin biopsies show marked dermal and epidermal atrophy. It is difficult, however, to perform a skin biopsy on these patients because skin can tear and the dermis may easily separate from the underlying adipose tissue.10

Without any underlying disease to treat, these patients can be difficult to manage. The skin wounds can be sutured, but skin will continue to tear easily unless the primary disease is identified and treated.

Alopecia

Alopecia can happen for numerous reasons. It is important to first establish if the alopecia is self-induced or spontaneous, which can be determined by performing a trichogram and observing the hair shaft integrity. The source of the alopecia can also be investigated by placing an Elizabethan collar on the patient and seeing if hair loss continues while the cat is restricted from grooming.

The location of the alopecia can help narrow down the list of differential diagnoses. For example, caudal ventral abdominal alopecia can be secondary to infection (bacteria, fungi, parasites) or allergies but could also be caused by urinary tract pain or other abdominal pain.

Some additional causes of alopecia are important to consider in an older feline patient. One of the most important is paraneoplastic alopecia. This alopecia is a cutaneous manifestation of a systemic disease, often adenocarcinoma of the pancreas or biliary tract. Paraneoplastic alopecia is usually acute in onset, rapidly progressive, and symmetrical, affecting the ventrum and limbs. The skin often has a very shiny, glistening appearance and can be thin, but is not fragile. Paw pads can also be involved (Figure 4).

4. A cat exhibiting alopecia and a glistening appearance of the skin associated with paraneoplastic alopecia. Note how the limbs and paws are also affected.

These patients often do not feel well, with concurrent weight loss and gastrointestinal signs. Skin biopsy can certainly help with a diagnosis, but thoracic and abdominal radiography or abdominal ultrasonography is more likely to find the causative neoplasia. If it is possible to remove the tumor or treat the cancer, hair can regrow.

Alopecia areata and pseudopelade are two rarer conditions that can cause alopecia. Both conditions cause a grossly noninflammatory, nonpruritic alopecia. In alopecia areata, lymphocytes invade the bulb of the anagen hairs, causing a patchy alopecia; in pseudopelade, the lymphocytic inflammation is within the isthmus, causing a diffuse alopecia.5

Other causes of alopecia in a geriatric cat include a cutaneous drug reaction, an endocrinopathy (especially hyperadrenocorticism), anagen/telogen defluxion, sebaceous adenitis, or an injection reaction. A skin biopsy is the most important diagnostic tool to help differentiate among the possible causes of alopecia in an older feline patient.

Pruritus

There are three general categories for any patient presenting with pruritus as the primary clinical sign—parasites, bacterial or fungal infection, and allergy. However, if the pruritus is a new clinical sign in an older cat, these broad categories can be narrowed down quickly. As has been previously stated, parasites can affect an animal at any age. Bacterial or fungal infection can also affect an animal of any age. In fact, geriatric patients are often predisposed to these conditions because of their age, especially if a patient has any other systemic diseases affecting the immune system.

It is especially important to look for evidence of demodicosis. Finding Demodex cati mites warrants a more thorough medical workup for a systemic disease predisposing the cat to unchecked mite proliferation.

If infection and parasites are ruled out and a feline patient remains pruritic, food allergy should be considered. It is unlikely that an older cat would develop environmental allergies, resulting in late-onset pruritus. A strict dietary trial with a home-cooked novel protein or a hydrolyzed protein commercial food should be performed. However, care should be taken to ensure that there are no other medical causes that need to be considered when designing the diet trial.11

Unilateral otitis externa or otitis media

Unilateral otitis externa or otitis media in an elderly cat with no history of ear disease is most likely secondary to an aural mass. An aggressive workup should be instituted at the initial examination. Perform an otoscopic examination to look for any abnormal tissue in the ear canal. This may need to be done under sedation if the cat is experiencing any pain or discomfort. The workup should include a complete blood count, a serum chemistry profile, a urinalysis, and imaging of the skull or bullae, ideally via computed tomography, but radiography or magnetic resonance imaging are other possibilities.

Often the treatment of choice is surgery to remove the ear canal. In certain cases, if the neoplasia is not aggressively invading surrounding soft tissue or the bone of the middle or inner ear or skull, surgery can be curative and provide a great deal of comfort to the cat.12

SUMMARY

Geriatric cats that are presented for evaluation of skin or coat changes can be a diagnostic challenge. Remembering to collect an appropriate history and perform core dermatologic tests will provide a solid basis on which to recommend further testing or treatment.

Darcie Kunder, VMD

Matthew J. Ryan Veterinary Hospital

University of Pennsylvania

Philadelphia, PA 19104

Karen A. Moriello, DVM, DACVD

Department of Medical Sciences

School of Veterinary Medicine

University of Wisconsin-Madison

Madison, WI 53706

References

1. Scott DW, Miller WH, Griffen CE, eds. Muller and Kirk's small animal dermatology. Philadelphia, Pa.: Saunders, 2001.

2. Guaguere E, Pascal P. A practical guide to feline dermatology. Merial, 1999.

3. Beale K. Feline demodicosis: a consideration in the itchy or overgrooming cat. J Feline Med Surg 2012;14(3):209-213.

4. Olivry T. A review of autoimmune skin diseases in domestic animals: I - Superficial pemphigus. Vet Dermatol 2006;17(5):291-305.

5. Turek MM. Cutaneous paraneoplastic syndromes in dogs and cats: a review of the literature. Vet Dermatol 2003;14(6):279-296.

6. Fontaine J, Heimann M, Day MJ. Cutaneous epitheliotropic T-cell lymphoma in the cat: a review of the literature and five new cases. Vet Dermatol 2011;22(5):454-461.

7. Boord, M, Griffin C. Progesterone secreting adrenal mass in a cat with clinical signs of hyperadrenocorticism. J Am Vet Med Assoc 1999;214(5):666-669.

8. Merchant SR, Taboada J. Systemic diseases with cutaneous manifestations. Vet Clin North Am Small Anim Pract 1995;25(4):945-959.

9. Sequeira JL, Rocha NS, Bandarra EP, et al. Collagen dysplasia (cutaneous asthenia) in a cat. Vet Pathol 1999;36(6):603-606.

10. Gunn-Moore D. Feline endocrinopathies. Vet Clin North Am Small Anim Pract 2005;35(1):171-210, vii.

11. Gaschen FP, Merchant SR. Adverse food reactions in dogs and cats. Vet Clin North Am Small Anim Pract 2011;41(2):361-379.

12. Kennis, RA. Feline otitis: diagnosis and treatment. Vet Clin North Am Small Anim Pract 2013;43(1): 51-56.