Alopecia in the cat Part

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					Alopecia in the cat: Part 2
Ewan Ferguson BVM&S DVD MRCVS

In the first of the articles on feline alopecia, the most       autosomal recessive trait. The Sphynx or
common cause of alopecia in the cat, hair loss due to           Canadian Hairless breed is the result of selective
self-trauma, was reviewed. In this, the second of the           breeding for a variant of the Cornish Rex gene.
series, alopecia arising from developmental                     The Sphynx allele is incompletely dominant
abnormalities or failure of intrinsic or extrinsic              over the Devon allele and both are recessive to
follicular control mechanisms is considered. Some of            the wild type. Crossbreeding with the Devon
these conditions, such as pattern alopecia or post-             Rex has led to serious dental or nervous system
inflammatory defluxion, are common, but most are                problems in the past.
comparatively rare. Some are confined to a specific
breed or are associated with specific diseases.

Broadly speaking, this group of alopecias fall into
several distinct categories:
1. Congenital and hereditary alopecias
2. Alopecia associated with acquired follicular
    pathology (intrinsic factors)
3. Alopecia arising from non-follicular pathology
    (extrinsic factors)

Ectodermal dysplasia
Rarely, areas of ectoderm fail to develop normally
during foetal development, which may lead to a
variety of clinical patterns affecting the follicles and
adnexae and skin.The prognosis depends entirely on
the extent and severity of the original lesion. Mild
cases may result in no more than areas of permanent
alopecia whilst more extensive lesions may heal by
secondary intention and produce extensive scarring.
The most severe cases are incompatible with survival.

Follicular dystrophy
Abnormalities in morphogens or structural proteins
result in hair shaft distortion or follicles that are so
                                                            Fig. 1: Devon Rex showing extensive congenital hypotrichosis. Note also the
malformed that hair growth is abnormal or                   marked pattern alopecia affecting the preauricular skin. This is normal in the
impossible. However, in general the follicular cycle is     breed.
maintained. As most of these conditions give rise to
abnormalities in hair shaft morphology, any alopecic
disease with no apparent follicular abnormality is
probably not a follicular dystrophy.

Hair shaft abnormalities
A variety of conditions affecting the shape,

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composition and strength of the hair shaft are
recognised in the cat:

1. Extensive congenital hypotrichosis may be seen
    in breeds such as the Cornish and Devon Rex
    (Fig. 1), Burmese, Birman, and Siamese. In the
    latter two breeds the condition is due to an

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    2. Trichorrhexis nodosa - nodular mid-shaft hair             alopecia may present as a transient, idiopathic
       fracture, usually an acquired defect and may be           condition in the Siamese.The cause is unknown and
       associated with infections (Fig. 2) or the                regrowth usually occurs spontaneously after several
       excessive use of shampoos. Overgrooming can               months.
       also produce similar hair shaft lesions and it is
       therefore imperative to rule out hypersensitivity         2. ALOPECIA ASSOCIATED WITH ACQUIRED
       and pruritus.                                             FOLLICULAR PATHOLOGY
                                                                 Traction alopecia
                                                                 Traction alopecia has been described in animals that
                                                                 have had elastic bands or other devices used to tie
                                                                 back the hair, usually on the head. If the device is
                                                                 applied too tightly or for too long, an atrophic
                                                                 alopecia may develop. Early lesions show a
                                                                 mononuclear infiltrate, oedema and vasodilation
                                                                 whilst chronic lesions progressively fibrose and show
                                                                 pilosebaceous atrophy.

                                                                 Demodicosis in the cat is caused by Demodex cati, D.
       Fig. 2: Trichorrhexis nodosa affecting the vibrissae of   gatoi and a third, still unnamed Demodex species. D.
       a Persian caused by focal bacterial infections.           cati inhabits the follicle and is morphologically
                                                                 similar to D. canis, although eggs and all immature
    3. Pili torti - flattening, rotation and exaggerated         stages are slightly slimmer. Demodicosis is a rare
       curvature of the hair shaft. Usually has a                condition in the cat usually presenting as patchy
       hereditary basis and may show other cutaneous             erythema, alopecia, scaling and crusting. Lesions are
       abnormalities. May selectively affect secondary           typically localised to the face, head and neck and the
       hairs. Localised pili torti can arise from                condition is usually self-limiting. It may occur as a
       folliculitis.                                             ceruminous otitis. Generalised demodicosis due to
    4. Shaft disorder of Abyssinian cats - rare. Only the        D. cati is rare and although not as severe as the canine
       vibrissae and primary hairs are affected.The hairs        form, many cases are associated with underlying
       are rough, dull and show bulbous swellings, often         disease such as diabetes mellitus, lupus erythematosus
       at the tip. An inherited disorder restricted to           or hyperadrenocorticism or immunocompromise
       Abyssinian cats, there is no effective treatment.         arising from feline leukaemia virus or feline
                                                                 immunodeficiency virus infection. Purebred Siamese
    Bulb matrix and melanocytes abnormalities                    and Burmese may be predisposed. D. gatoi inhabits
    1. A form of follicular dysplasia has been reported          the superficial interfollicular stratum corneum and
       in the Cornish Rex associated with the presence           can be associated with severe disease suggestive of
       of abnormal clumped macromelanosomes                      scabies or hypersensitivity. Common lesions include
       distorting hair shaft anatomy. This condition is          scaling, excoriations, crusting, multifocal erythema
       slowly progressive resulting in symmetrical               and hyperpigmentation with secondary self-inflicted
       truncal alopecia.                                         alopecia. It is contagious and all in-contact animals
                                                                 should be treated.
    2. Cats with blue or cream coloured coats carry the
       Maltese dilution gene resulting in clumping of            Amitraz rinses and ivermectin have been used
       melanosomes in the hair shafts and follicular             successfully to treat both forms of demodicosis.A full
       epithelium. However, hair shaft pathology and             discussion of treatment options lies beyond the scope
       dysplastic changes in the follicle are rare.              of this article and more detailed information should
                                                                 be sought before embarking on treatment. These
    Pattern alopecia                                             products are not licensed for use in cats; there are at
    Pattern alopecia occurs as a symmetrical diffuse             present no products with such a licence.
    thinning of the hair coat in specific regions of the
    body. One example, seen in most cats, is preauricular        Dermatophytosis
    pattern alopecia. Vellous transformation or                  Feline dermatophytosis most commonly presents as
    miniaturisation of the follicles may be seen. Pinnal         one or more irregular patches of alopecia.The hairs
                                                                 in affected areas are broken and frayed and the skin
                                                                 may show a variable degree of scaling. Follicular
                                                                 hyperkeratosis gives rise to follicular plugging and

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                                                                 comedo formation. There may be minimal

                                                                 inflammation whilst other cases may show areas of
                                                                 folliculitis, erythema, scale, crust and follicular
                                                                 papules. Recurrent folliculitis resembling feline acne or
                                                                 stud tail can be seen. Widespread, pruritic, exfoliative

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erythroderma with extensive secondary self-inflicted           destruction of the follicles with haemorrhage and
alopecia may be observed. Dermatophyte kerions                 oedema. Arthropod bites are the most common
occurs occasionally whilst dermatophytic pseudo-               triggers with mosquito bite hyper-sensitivity
mycetomas have been reported only in Persians.                 being a good example. Rarely, cutaneous drug
                                                               reactions, feline herpes virus dermatitis and
Fungal culture is required to speciate dermatophyte            ischaemia produce a cell-poor or neutrophil
infections, as this cannot reliably be inferred from the       dominated necrotising mural folliculitis.
clinical lesions.                                          G   Pustular mural folliculitis describes the
                                                               formation of microabscesses and pustules within
Folliculitis                                                   the wall of the outer root sheath. Examples of
A number of distinct pathological patterns are                 this pattern are seen in follicular pemphigus
recognised though not all have been specifically               foliaceus and pemphigus erythematosus or
described in the cat. All patterns lead to varying             panepidermal pemphigus.
degrees of alopecia, often with other accompanying
clinical signs which may help the clinician                3. Luminal folliculitis
differentiate between these conditions:                    This is the most widely recognised histological
1. Perifolliculitis                                        pattern of folliculitis. It is usually associated with
Describes an inflammatory reaction surrounding, but        invasion of the follicle by infectious agents.
not infiltrating, the outer root sheath of the follicle    Inflammatory cells, normally neutrophils, migrate
which does not cause basal cell destruction. Where         into the follicular lumen before releasing their
only the follicular ostia is involved, this is more        inflammatory mediators. As a result, mural destruction
properly described as a spongiotic dermatitis.             starts from the inside of the follicle rather than the
Examples in the cat would include acute                    outside, as in the mural folliculitides. Bacterial
hypersensitivity triggered dermatitis, leishmaniasis       folliculitis, dermatophytosis and demodicosis typically
and some forms of sebaceous adenitis.                      produce this pattern.

2. Mural folliculitis                                      4. Bulbitis
Occurs when the inflammatory process targets the           In this pattern, a lymphocytic inflammatory pattern
wall, or outer root sheath, of the follicle and the        is targeted at the inferior portion of the follicle.This
lumen is spared. Four main subdivisions are                occurs in alopecia areata - since the follicular stem
recognised:                                                cells reside higher up the follicle and are not placed
G   Interface mural folliculitis is a relatively non-      at risk by any mural involvement, spontaneous
    specific pattern often seen with perifolliculitis.     recovery usually occurs over time.
    The basal cell layer may be targeted with varying
    severity, resulting in hydropic change, and            3. ALOPECIA ARISING FROM NON-FOLLICULAR
    keratinocyte apoptosis. Conditions where this          PATHOLOGY
    pattern is seen include lupus erythematosus,           Hair cycle abnormalities
    erythema multiforme, cutaneous adverse drug            1. Alopecias associated with systemic disease
    reactions, thymoma-associated exfoliative              In the dog, alopecia is a common feature of
    dermatitis and various vasculitides and                endocrine disease whereas in the cat, it is much less
    vasculopathies, such as rabies vaccination             commonly encountered. Hyperadrenocorticism
    reactions where a scarring alopecia resulting          occurs typically in middle-aged to older cats.
    from follicular destruction and secondary fibrosis     Females are more commonly affected but there is
    occurs.                                                no breed predisposition. Clinical signs include
G   Infiltrative mural folliculitis occurs when there is   polyuria/polydipsia, weight loss, muscle wasting, skin
    infiltration of the follicle wall by lymphocytes       fragility, comedone formation and seborrhoea.
    and histiocytes without accompanying hydropic          Medial curling of the ear tips is seen in iatrogenic
    degeneration and apoptosis. A variable degree of       hyperglucocorticism but has not been reported in
    mural destruction may be seen. In feline               naturally occurring hyperadrenocorticism. Skin
    idiopathic lymphocytic mural folliculitis and          changes, including alopecia, only occur in
    primary sebaceous adenitis; mural damage does          approximately 50% of cases. Ninety per cent of
    not occur whereas in secondary sebaceous               affected cats are prediabetic or overtly diabetic due
    adenitis, the outer root sheath is destroyed in a      to the insulin antagonistic activity of cortisol. The
    number of patterns. Other conditions showing           diabetes frequently becomes subclinical after
    this infiltrative pattern include pseudopelade,        successful management of the hyperadrenocorticism.
    early epitheliotrophic lymphoma and alopecia           Cats often present late in the course of the disease,
    mucinosa where accompanying mucinosis of the           which then carries a poorer prognosis due to the
    outer root sheath is seen.                             advanced development of degenerative changes and
G   Necrotising mural folliculitis may be considered       diabetes mellitus.
    as a distinct pattern of infiltrative mural
    folliculitis. The inflammatory infiltrate is usually   Biochemical and haematological changes are of
    eosinophil-dominated and may cause explosive           limited diagnostic specificity. More than 20% of cats

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    do not show adrenal suppression with 0.01 mg/kg of           are recognised in man but such subdivision, whilst
    dexamethasone and a dose of 0.1 mg/kg is suggested           perhaps applicable, has not been undertaken in
    for suppression testing. All cats with hyper-                animals.
    adrenocorticism have failed to suppress to normal
    levels (<10 µg/l). Most affected cats will show an           2. Alopecias associated with abnormalities
    exaggerated response to ACTH but equivocal or                localised to the follicle and surrounding tissues
    normal responses can be seen. Response to medical            (paracrinopathies, autocrinopathies)
    treatment is variable and some clinicians suggest            G   Post-inflammatory alopecia
    bilateral adrenalectomy as the treatment of choice.              Following any episode of acute inflammation,
                                                                     overlying skin frequently exhibits an abrupt,
    Congenital hypothyroidism has been reported in the               complete shedding of the hair coat resulting in
    cat and leads to decreased growth rates, stunting,               total alopecia in a well-demarcated patch
    lethargy and dwarfism.The coats are full but dry and             overlying the inflamed tissue. A typical example
    lacking in primary hairs. Spontaneous hypothyroidism             would be the hair loss seen in skin surrounding
    occurs very rarely and has produced a dull dry,                  and overlying a cat bite abscess. The hairs are
    seborrhoeic coat with poor regrowth. Cats                        telogenised, easily epilated and lost in large
    undergoing radioablation of the thyroid glands                   clumps. This form of loss probably represents an
    resulting in induced hypothyroidism exhibited                    immediate telogen release (Type 4 telogen
    transient lethargy, coat matting, seborrhoea and                 defluxion) where normal telogen is shortened
    alopecia of pressure points, pinnae and dorsal and               and hair loss begins within a few days.
    lateral tail base.
                                                                     In chronic inflammatory dermatitis, diffuse
    Cutaneous abnormalities occur in approximately                   alopecia may also develop. Rather than complete
    30% of cats with hyperthyroidism and include                     alopecia, there is a progressive thinning of the
    excessive shedding and focal or symmetrical alopecia             coat and this again probably represents a variant
    associated with overgrooming. Chronic cases may                  of telogen defluxion.
    mimic hyperadrenocorticism with thin, hypotonic
    skin and extensive truncal alopecia.                         G   Topical ‘spot-on’ reactions
                                                                     The trend towards the formulation of routine
    Hyperoestrogenism and oestrogen responsive                       ectoparasiticides as topical ‘spot-on’ products has
    dermatosis will produce alopecia in the dog but are              given rise to the appearance of a novel focal
    extremely rare in the cat.                                       alopecia. This takes the form of a well-defined
                                                                     focal patch of alopecia appearing at the site of
    Diabetes mellitus is a common feline endocrinopathy              administration within a few days of treatment. It
    and may also result in changes similar to those seen             may be preceded by localised pruritus or
    in hyperthyroidism. Thin, hypotonic skin with                    irritation and mild localised crusting. It is most
    variable alopecia and generalised seborrhoea are the             likely to represent an adverse reaction to the
    more common cutaneous signs. Xanthomatosis has                   vehicle used in the formulation rather than the
    also been reported in both naturally occurring and               active agent. The alopecia and irritation are
    megestrol acetate-induced diabetes mellitus.                     transient but may recur on reapplication of the
                                                                     same product. Substitution with a different ‘spot-
    Anagen defluxion occurs when a severe insult occurs              on’ formulation is indicated.
    to the anagen follicles, resulting in abnormalities of the
    follicle and hair shaft. As anagen progresses, hair loss     Atrophic abnormalities
    occurs abruptly, within days of the insult. Examples         1. Depot glucocorticoid atrophy
    of triggers that can potentially induce anagen               Local, well demarcated patches of alopecia associated
    defluxion include therapy with anti-mitotic drugs,           with pigmentary changes and dermal, epidermal and
    infectious disease and exposure to a range of toxins.        adnexal atrophy may be seen. The injected material
                                                                 may be visible through the atrophic skin and the
    Telogen defluxion occurs 4-12 weeks after an episode         tissues are palpably thinner than surrounding skin.
    of physiological stress such as severe illness or            The changes may not be reversible. Focal alopecia
    pyrexia, shock, surgery or anaesthesia. It may also          has also been reported with the use of topical
    occur following the removal of an abnormal                   glucocorticoid preparations, typically at the base of
    telogenising influence such as an endocrinologically         the pinna following administration of otic products.
    active neoplasm, correction of a systemic
    endocrinopathy such as hyperadrenocorticism or               2. Vellous transformation
    withdrawal of glucocorticoid or progestagen therapy.         Progressive telogenisation and miniaturisation of the
    In all cases, premature cessation of the anagen phase        follicle, progressing through to atrophy. Small scaled-
    results in synchronisation of the follicles in catagen       down hairs may be produced or the follicle may be
    and then telogen. As a new wave of hairs is                  lost. This pattern is seen in paraneoplastic alopecia
    produced, the telogen hairs are shed in synchrony.           (Fig. 3) where hair is easily epilated all over the body.
    Several distinct functional types of telogen defluxion       The syndrome presents in older cats with a history

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                    of weight loss, lethargy and inappetance. The skin                  in the genital and perineal regions is the most
                    becomes characteristically smooth, shiny and alopecic.              common initial presentation. This may progress to
                    Adnexal atrophy may be severe. A diagnosis of                       thinning of the coat over the lateral thorax and flanks
                    pancreatic neoplasia of either acinar cell or pancreatic            but the dorsum is usually unaffected. Pruritus and
                    duct origin is usually made on exploratory                          skin lesions are absent.
                    laparotomy. The prognosis is usually grave although
                    early surgical intervention may be curative.                        Since overgrooming can produce an identical pattern,
                                                                                        it is essential to eliminate self-trauma as a cause. Cats
                                                                                        can be secretive about grooming, particularly if the
                                                                                        activity attracts unwelcome attention. Close
                                                                                        examination of plucked hairs will help identify those
                                                                                        animals where self-trauma is playing a role and these
                                                                                        will, in general, far outnumber those where acquired
                                                                                        symmetrical alopecia is a genuine differential.

                                                                                        Conflicting reports on the thyroid status of cats with
                                                                                        this syndrome have been published but as a group,
                                                                                        there appears to be a depressed TSH response.
                                                                                        Therapy with T3 has been recommended but
                                                                                        combined androgen-oestrogen therapy appears to be
                                                                                        more successful. Progestagens have also been used
Fig. 4: Paraneoplastic alopecia in a domestic shorthaired cat. Note the                 but bearing in mind the occasionally severe adverse
characteristic smooth, shiny, alopecic appearance of the skin. (Illustration courtesy   effects associated with all these treatments, full
of Dr Ross Bond, RVC.)
                                                                                        consideration should be given to the benign, non-
                                                                                        life-threatening and essentially cosmetic nature of
                    3. Arrested follicular cycle                                        this condition.
                    Some older cats develop thick, dense coats that
                    become dry, brittle and faded, sometimes                            In summary, when confronted by alopecia in the cat,
                    accompanied by mild diffuse scaling.This appears to                 it should be remembered that the vast majority of
                    occur because the follicular cycle becomes                          cases eventually prove to be self-inflicted. Only after
                    prolonged or arrested, remaining in telogen for an                  overgrooming has been definitively excluded,
                    extended period. Hairs are progressively damaged by                 whether by dietary trials or parasite control, on the
                    mechanical, chemical and physical insult and the                    basis of clinical history or biopsy or even through
                    melanin is gradually photodegraded, leading to                      therapeutic trials with antipruritics should
                    fading of hair shaft pigmentation. Hairs are shed but               alternative differentials be considered.
                    not replaced and over a long period, patches of
                    alopecia can develop in areas subject to rubbing or
                    overgrooming. In the absence of any recognisable
                    systemic disease, follicular senescence is the most
                    likely cause.

                    4. Scleroderma
                    Localised scleroderma (morphea) is a rare disease and
                    the cause and pathogenesis are unknown. Proposed
                    pathomechanisms include vascular injury or
                    malfunction, abnormal collagen metabolism and an
                    immunological mechanism mediated through
                    humoral and cell-mediated autoimmunity. Lesions
                    are typically well demarcated, asymptomatic, smooth,
                    shiny and alopecic. Hypopigmentation may be seen.
                    The trunk and limbs are most commonly affected
                    and diagnosis is confirmed by biopsy. Some lesions
                    recover spontaneously and in others, permanent
                    scarring results. Changes in hair colour, size and
                    texture may be seen on regrowth.

                    Feline acquired symmetrical alopecia
                    This is a rare condition seen principally in neutered
                    animals. No breed predilection is reported but
                    purebred cats are rarely affected. The mean age of
                    onset is six years but there is a wide (2-12 years)
                    range. Diffuse thinning of the hair coat, principally

                    UK Vet - Vol 13 No 1 January 2008                                                      SMALL ANIMAL G DERMATOLOGY ##            5
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     These multiple choice questions are based on the above
     text. Answers appear on page 99.
     1. Which of the following statements are INCORRECT:
        a. Demodicosis caused by D. gatoi is usually pruritic
           and may be contagious.
        b. Feline dermatophytosis may cause widespread
        c. Dermatophytic pseudomycetomas have been
           reported only in the Persian.
        d. Skin changes are present in 90% of feline
           hyperadrenocorticism cases.
        e. Pili torti is an inherited hair shaft defect seen in
           Abyssinian cats.

     2. Which of the following statements are CORRECT:
        a. Alopecia areata is a self-limiting disease caused by a
           mural folliculitis.
        b. Arthropod bites are the most common cause of
           necrotising mural folliculitis.
        c. Sebaceous adenitis typically causes a luminal
        d. Vellous transformation is seen in pattern alopecia.
        e. Cutaneous changes occur in approximately 30% of
           hyperthyroid cats.

6   SMALL ANIMAL G DERMATOLOGY ##                                   UK Vet - Vol 13 No 1 January 2008

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