Bald Is not beautiful, if you are a cat: managing alopecia in cats (Proceedings)

The Feline Hair Follicle

Cats have compound hair follicles. In general, there is a cluster of two to five primary hairs surrounded by groups of smaller secondary hairs. One primary hair is the largest (central) surrounded by groups of small primary hairs (lateral primary hairs). Each primary hair has a sebaceous gland, arrector pili muscle, sweat gland. Secondary hairs may only have a sebaceous gland. Five to 20 secondary hairs may accompany each primary hair.  The two most common specialized hairs are sinus hairs (whiskers) and tylotrich hairs.

Skin Biopsy: When, Where, and How

When-Timing in the Diagnostic Approach: In general, the longer a disease process is present the more likely, that the classic findings associated with the underlying disease will be obscured by inflammatory changes. Systemic drugs can and do affect cellular infiltrates in skin biopsy specimens. No studies have been conducted on appropriate wash out periods; use the same washout periods for skin biopsy that are used for intradermal skin testing.  If topical therapy is being used, allow for at least a one-week washout period.

Where-Lesion Selection: Skin biopsy specimens from cats with alopecia should include as many representative samples as possible, including a “normal” site. The latter will allow for comparison of the cellular filtrate and hair follicle stages between normal and abnormal. Avoid areas of with significant trauma; look for primary lesions. The skin should not be prepped in any way prior to the sampling.

How-Getting a Better Skin Biopsy: Skin biopsy specimens should be obtained under heavy sedation and concurrent local anaesthesia. The skin should not be prepped to avoid losing important surface finding and or prevent introduction of artefacts. The use of a new skin biopsy punch is recommended; this will avoid the introduction of shear. Harvest the biopsy with care to avoid introduction of crush artefact. The skin of cats is thin and should be placed between foam in a biopsy cartridge or on a wooden tongue depressor, (this can cause dehydration and shrinkage). It is very important to allow the specimen to fix for at least 24 hours before being sectioned by the pathologist. If it is necessary to submit all of the specimens in one containing making it difficult to label the specimens, biopsy cartridges are strongly recommended because important information can be written on the flattened front.  If these are not available, a small part of the biopsy can be marked with a black sharpie and then a notation made for the pathologist. It is VERY important to take a large enough specimen so that many hair follicles are present and to leave the hairs long enough that the pathologist can see them grossly. If the hairs cannot be seen at the time of bisection, the specimen may not be oriented properly resulting in a “swiss cheese” cut versus a cut parallel to the hair follicles.

Clinical Presentations

Alopecia in cats can be focal, multi-focal, or wide spread (regionally or generalized). The alopecia may be inflammatory or non-inflammatory. Inflammatory alopecia is usually characterized by any combination of concurrent papules, military dermatitis, exudation, follicular plugging, scaling, and broken hairs. Cats with inflammatory alopecia are usually presented for both hair loss and pruritus.

Diagnostic Tests

Diagnostic tests should be selected based upon history, clinical signs, clinical acumen, probability or necessity to rule out a diagnosis, and common sense.  A diagnostic test should answer a question and the reason for a diagnostic test should not be “minimum data base”.

Highly Indicated at First Presentation

Skin scrapings, flea combings and fecal examinations are useful for ruling in a diagnosis, but a negative test in a cat does not necessarily rule out parasitic skin diseases. If negative, a response to treatment trial may rule in/out a differential diagnosis.

Wood's lamp examination is helpful if positive as it allows the clinician to sample hairs and look for evidence of Microsporum canis infection. This test helpful if positive but a negative test is inconclusive.  This is an inexpensive and atraumatic test; Wood's lamps are time and cost effective when used in high at risk populations (e.g. kittens with hair loss, inflammatory skin lesions).

Fungal culture can be argued as “always indicated” because dermatophytosis is a disease of hair follicles. If a Wood's examination is positive, a culture is indicated. If the cat is in a high risk/high suspicion group, a culture is indicated. If the owner is seeking a second opinion, a culture is indicated. This is the most expensive diagnostic test in the “highly indicated” group or core diagnostics and the one test where results are not immediately available. If other core diagnostics are negative and a fungal culture is pending, consideration needs to given to “treatment pending diagnosis”.

A hair trichogram is helpful when the Wood's lamp examination is positive, hairs are shedding with little traction (can help confirm an effluvium), and when looking for Demodex mites (i.e. D. gatoi).  Plucking of hairs can cause damage to the shaft; examine hairs with care and do not over interpret.

Ear swab cytology and mineral oil swabs may be helpful in identifying ear mites, Demodex mites, and are indicated where there is hair loss on the head and neck.

Skin cytology is used primarily to look for Malassezia organisms; cats can have antibiotic responsive skin lesions and yet bacteria or inflammatory cells are not seen.

Less Commonly Indicated at First Presentation

With the exception of an eosinophil count, a CBC, a serum chemistry panel, a urinalysis and/or a T4 are rarely helpful at first presentation assuming the cat is not showing clinical signs of systemic disease. Eosinophil counts are often elevated in cats with hair loss due to fleas/flea allergy.

A skin biopsy can be indicated at first presentation in cases of focal non-inflammatory alopecia if core diagnostic tests (excluding fungal culture) do not identify a cause. A skin biopsy is indicated at first presentation if clinical signs are unusual or life threatening or progressing rapidly. If clients are frustrated (second opinion clients) and core diagnostic tests have not identified a cause, a skin biopsy may be indicated in the early diagnostic process. Sometimes this is a necessary diagnostic test if clients are very anxious and need assurance no life threatening disease is present before they will participate in a response to treatment trial(s).

Food Trial and/or Allergy Testing are rarely indicated at the time of first presentation. The results of routine diagnostic tests and response to treatment trials should be documented prior to embarking on a food trial or performing an allergy test.  In second opinion clients, all medical records and diagnostic testing should be examined prior performing either of these diagnostic tests and a time line should be constructed for all diagnostic tests. Second opinion clients often present cats with long complicated histories and have spent a lot of money on diagnostics tests. For diagnostic tests to be helpful, they need to be performed in a reasonable time-period and in a logical order. Clients are much more willing to “back track” and repeat diagnostic and/or response to treatment trials with visual aide that shows the progression of diagnostic tests, gaps in testing or treatment etc. “Visual aids” require pencil, paper and time. 

Response to Treatment Trials (Multi Focal or Widespread Alopecia)

If core diagnostic tests do not identify a cause for multi-focal or widespread alopecia, a treatment trial is indicated. This of course is assuming that there are no signs and/or suspicion of systemic disease and/or the hair loss is not alarming in clinical presentation.

Response to Flea Control: Spot on treatments at zero, 30 and 60 days or once weekly treatment with a topical flea spray will rule out fleas, migrating ear mites, Cheyletiella mites, Notoedres mites.

Response to Antimicrobial Treatment: This involves a 30 days treatment of a combined antibiotic and oral antifungal (e.g. 25 mg/k cat of itraconazole-use compounding pharmacy). Itraconazole can be administered once daily for 30 days or used on a week on/week off protocol.

Response to Lime sulphur: Lime sulphur is an effective whole body treatment for D. gatoi,D. cati,Cheyletiella, Notoedres, migrating ear mites, lice and dermatophytosis. Treatment trials are usually 6 weeks- once or twice-weekly treatment with a 1:16 or 1:32 dilution of lime sulphur.  If dermatophytosis is diagnosed, treatment should continue until the cat is repeatedly culture negative.

Advanced Diagnostic Testing

Urinalysis-Metabolic disease or ventral abdominal alopecia (cystitis)

Abdominal Ultrasound/Abdominal Radiographs-ventral abdominal alopecia, paraneoplastic alopecia

CBC, Serum Chemistry Panel-metabolic disease

Food Trial

Allergy Testing (serum or intradermal testing, a negative test does not rule out allergies)

Skin Biopsy-hair follicle dysplasia, neoplasia, and paraneoplastic syndrome

Response to treatment trial with glucocorticoids, cyclosporine

Causes of Feline Alopecia

Causes of focal to diffuse inflammatory alopecia include feline demodicosis, fleas and flea allergy, parasitic mites, lice, bacterial pyoderma and Malassezia dermatitis (always secondary to another trigger), dermatophytosis, food allergy, atopy, idiopathic hypersensitivity (steroid responsive skin disease with no determined underlying cause).

Causes of non-inflammatory focal alopecia include post traumatic alopecia, post injection alopecia, post spot-on flea control alopecia, pattern baldness, pre-auricular alopecia, traction alopecia, alopecia areata, and anagen or telogen defluxion. Parasitic and infectious skin diseases tend to be inflammatory but can present as non-inflammatory focal lesions when first developing. 

Causes of non-inflammatory multifocal to diffuse alopecia include.  Congenital or Hereditary: breed associated alopecia, alopecia universalis, hereditary hypotrichosis, follicular dysplasia; Associated With Clinical Signs of Systemic Disease: cystitis, inflammatory bowel disease, anagen or telogen defluxion, feline hyperadrenocorticism, feline paraneoplastic alopecia, degenerative mucinotic mural folliculitis, Otherwise Healthy Cat: anal sac disease, psychogenic alopecia, sebaceous gland dysplasia, pseudopelade