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3. small Anim. Pract. (1971) 12, 445-452. Intradermal tests as an aid to the diagnosis of skin disease in dogs* K. P. BAKER Department of Clinical Veterinary Practices, School of Veterinary Medicine, University of Dublin, Ballsbridge, Duhlin, 4 ABSTRACT The diagnosis and treatment of skin disease form a major part of the small animal practitioner’s work. A significant number of cases will be allergic in nature and may present difficulties in diagnosis. In man, skin testing for allergy is an established aid to diagnosis, but has been little used by the small animal veterinarian; published results are few. This paper is a pre- liminary report of the results of skin tests using allergens on normal and allergic dogs. It is considered that the method is of value as an aid to the diagnosis of flea hypersensitivity, but that the preliminary results using other allergens are inconclusive. INTRODUCTION A proportion of cases of canine skin disease will prove difficult to diagnose. Many of these will show pruritus without visible cause. The practitioner may be able to eliminate common causes-such as mites, lice, fleas and ringworm but still be left with a pruritic animal which may or may not show skin lesions of an appar- ently non-specific type. He may then feel a need for further diagnostic aids to en- able him to proceed further to a diagnosis. However, it is all too easy at this stage to prescribe corticosteroids to allay the patient’s irritation and thus to satisfy the client-for a time. Probably a significant number of such dermatoses are allergic in nature. Allergic reactions result from secondary exposure of a host to allergens. They are, therefore, to be differentiated from certain idiosyncratic reactions of certain individuals to some substances to which they have not been previously exposed. Walton (1966) lists four * Presented to a symposium on Canine Dermatology, 14th B.S.A.V.A. Congress, London, 1971. 445

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Page 1: Intradermal tests as an aid to the diagnosis of skin disease in dogs

3. small Anim. Pract. (1971) 12, 445-452.

Intradermal tests as an aid to the diagnosis of skin disease in dogs*

K . P. B A K E R

Department of Clinical Veterinary Practices, School of Veterinary Medicine, University of Dublin, Ballsbridge, Duhlin, 4

A B S T R A C T

The diagnosis and treatment of skin disease form a major part of the small animal practitioner’s work. A significant number of cases will be allergic in nature and may present difficulties in diagnosis. In man, skin testing for allergy is an established aid to diagnosis, but has been little used by the small animal veterinarian; published results are few. This paper is a pre- liminary report of the results of skin tests using allergens on normal and allergic dogs. I t is considered that the method is of value as an aid to the diagnosis of flea hypersensitivity, but that the preliminary results using other allergens are inconclusive.

I N T R O D U C T I O N

A proportion of cases of canine skin disease will prove difficult to diagnose. Many of these will show pruritus without visible cause. The practitioner may be able to eliminate common causes-such as mites, lice, fleas and ringworm but still be left with a pruritic animal which may or may not show skin lesions of an appar- ently non-specific type. He may then feel a need for further diagnostic aids to en- able him to proceed further to a diagnosis. However, it is all too easy at this stage to prescribe corticosteroids to allay the patient’s irritation and thus to satisfy the client-for a time.

Probably a significant number of such dermatoses are allergic in nature. Allergic reactions result from secondary exposure of a host to allergens. They are, therefore, to be differentiated from certain idiosyncratic reactions of certain individuals to some substances to which they have not been previously exposed. Walton (1966) lists four

* Presented to a symposium on Canine Dermatology, 14th B.S.A.V.A. Congress, London, 1971.

445

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446 K. P. B A K E R

types of agents which can induce allergic reactions in the skin of dogs and cats: (1) Ectoparasites (fleas, biting-flies). (2) Contact allergens (rubber, soft furnishings). (3) Ingested, injected and inhaled allergens (foods, drugs, pollen). (4) Internal allergens (parasitic intestinal helminths) .

Of these, ectoparasites are probably the most common cause of allergic dermatitis. Walton (1967) considers that in dogs and cats with skin disease entering a general clinic, ingested allergens are responsible for only 1 % of cases. No figures are avail- able for the incidence of allergy in dogs associated with inhaled allergens.

Diagnosis of allergy may be attempted in several ways. I t may be undertaken by in uiuo tests which involve the exposure of the skinof the host tospeciiic allergens, as in intradermal tests. I t may also be attempted by in uitro tests; degranulation of basophils by the patient’s serum and suspect allergen is an example.

Skin-testing of dogs to detect allergic response was first undertaken by Burns (1933). Since that time the method has received some popularity among veterinar- ians in the United States as an aid to the diagnosis. Published results, however, are very few. In man, skin-testing for allergy is widely used for the identification of the allergens associated with, for example, asthma, hay fever, allergic migraine : even so, it is considered unreliable by some authorities (Rook, Wilkinson & Ebling, 1970).

In an attempt to determine the value of intradermal testing for the diagnosis of allergy in dogs the work reported here was undertaken. I t is an interim report and it is hoped later to record the results of further tests.

MATERIALS AND M E T H O D S

In man tests for pollen and food allergens are normally made by the prick method, the intradermal test being preferred for testing inhalant allergens. Because of this, the former method was initially used by the author.

For cosmetic reasons, the site chosen for the skin tests was the ventral abdomen; also in many dogs the abdominal skin is relatively devoid of hair and only slight clipping is required. The animals were restrained in dorsal recumbency and most of them lay quietly for the procedure. An area of the skin of the abdomen approxi- mately 15 cm x 12 cm was clipped. When severe skin reactions were present there was little normal skin available on which to perform skin tests. In such cases it was possible to undertake only two or three tests at a time. Tranquillization was never used because of the reported interference with test readings. The skin was not shaved after clipping because this procedure may cause a marked skin reaction and consequently interfere with the reading of the tests. Where necessary the skin was-cleaned’;vith 0.5 % phenol saline. Bencard-prick and intradermal test solutions were used-for skin tests; for each prick-test one drop of the test solution (for prick testing, 0.5%) was placed on the skin and the skin lightly pricked through the drop with a Bencard prick test instrument. *

* Bencard-Brentford, England.

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D I A G N O S I S O F S K I N D I S E A S E 447

Intradermal tests were made with Bencard 2% solutions except when the flea allergen was used. A small bleb (3 mm in diameter) of each allergen was intro- duced at sites 3 cm apart using a in. No. 25 needle attached to a 2.5 ml disposable syringe. The needle was introduced into the superficial dermis with the bevel up, care being taken to avoid introducing the test solutions subcutaneously. Test solutions chosen represented examples of the various allergens to which dogs might be expected to have been exposed. Inhalant allergens were represented by house dust, kapok, sheep wool, pollens, mould mix; ingested allergens by meat, milk, fish, wheat and cabbage. For each technique a control injection of normal saline was made into the skin.

Initially, an American commercial flea allergen was used but this proved un- satisfactory and subsequently an extract was made from crushed whole fleas, obtained from dogs. This was prepared by grinding in a mortar a weighed mass of killed fleas with a little phenol saline and making up to a concentration of 1 : 1000 with phenol saline; the fluid was filtered through a Seitz filter and finally placed in an incubator at 65°C for 1 hr.

Tree pollen, grass pollen, mixed weed pollen, house dust, kapok, sheep wool, milk, meat, fish were the prick solutions used.

Readings were recorded as follows :

Prick tests Intradermal tests

- No wheal + No wheal, but slight

- No increase in size of bIeb + Wheal up to 5 mm diameter

erythema, up to 3 mm in diameter Wheal up to 3 mm diameter

+ + + Wheal of 5-8 mm diameter

+ + + Wheal of 8-12 mm diameter

I n each case the injection sites were compared with the control sites: reactions to allergen were only regarded as positive if they exceeded, by the above figures, any reaction at the control site. Adrenaline injection B.P. was available to counter- act the effects of an anaphylactic reaction, but no such reaction was observed in the present series.

Both normal and suspected allergic dogs were tested in this study. Results are shown in Tables 1-4. As there are very few published reports of the effects of intra- dermal tests with allergens on normal dogs, it was thought necessary to examine their effect on the normal so that comparison could be made with the abnormal. Allergic dogs were submitted for examination at a general veterinary clinic in Dublin, the diagnosis of allergy being made on the clinical history and by the elimination of other causes.

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448 K . P. B A K E R

To determine the effect of corticosteroids on skin tests the following experiment was undertaken :

Two normal dogs received the following injections: Dog (1) received 2 mg Betsolan* intramuscularly, Dog (2) received 40 mg Depomedrone t intramuscularly, a third normal dog acted as control and was not injected with a corticosteroid. Twenty-four hours later a sufficient volume of 1 : 1000 histamine solution to raise a bleb 0-3 cm diameter was injected into the dermis of the ventral abdomen of each animal. The sites were examined after 15 min and any reaction measured. Using different sites, injection of histamine was repeated 8 and 30 days after the injection of corticosteroids. Results are shown in Table 5.

A dog which had clinical signs of flea hypersensitivity was injected intra- muscularly with 10 mg Vecortenolf. One day and 35 days later it was challenged with flea allergen. The results which were observed immediately subsequent to intradermal injection, and at 15 min later are shown in Table 6.

R E S U L T S

TABLE 1. Skin tests-normal dogs

No. of dogs Prick tests Intradermal test

17

10

Control, fish, meat, milk, house dust. No dog reacted positively

Control, flea. One positive reaction in a dog harbouring fleas Control, cabbage, meat, milk, house dust. No dogs reacted positively

TABLE 2. Skin reactions in dogs with allergic dermatitis (other than flea hypersensitivity) to

various allergens

No. tested AIlergen used Reason

Prick test 10 Fish 10 -ve 8 Meat 8 -ve

14 Milk 2 +ve 4 Weed pollen 1 +ve

14 Grass pollen 2 +ve 4 Tree pollen 4 -ve 6 Moulds 6 -ve

* Betsolan-betamethasone (Glaxo). t Depomedrone-methylprednisolone acetate (Upjohn). 1 Vecortenol-prednisolone (Ciba).

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D I A G N O S I S O F S K I N D I S E A S E

Table 2. Cont.

449

No. tested Allergen used Reason

Intradermal tests 15 11 3 5 5 5 2

House dust 5 +ve Kapok 4 +ve Sheep wool 3 -ve Milk 5 -ve Meat 5 -ve Cabbage 2 +ve Mould mix 2 +ve

TABLE 3. Flea hypersensitivity. Skin reactions to intradermal flea extracts in dogs with clinical flea hypersensitivity

Reactions ~~ ~

No. tested +ve - ve % +ve

34 25 9 73.5

Four dogs showed + + reactions to flea extracts but also a similar reaction to the control injection and are therefore not included.

TABLE 4. Type of positive reaction of flea allergen

Immediate 15 min 1 h r 1 day

Number reacting 0 24 24 24

Sixty-nine per cent ofpositive reactions were of + + + or more, the reaction being quite obvious by 5 min, reaching a maximum diameter by 15 min and remaining apparent for up to 24 hr. No positive reactions were delayed longer than 15 min.

TABLE 5. Effect of corticosteroid on the reaction to intradermal histamine. Increase in size of bleb

after 15 min

Day Control Dog I * Dog 2 t

1 0.4 mm 0 1 mm 8 0.4 mm 0 2 mm

30 0.2 mm 0 0 mm

* 2 mg betamethasone. t 40 mg methylprednisolone acetate.

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450 K. P. B A K E R

TABLE 6. Effect of corticosteroid on the reactivity of the skin to flea allergen in a dog with flea hypersensitivity

Day 1 Day 35

Omin 15 min Omin 15min

Control -ve -ve -ve -ve Flea allergen -ve -ve -ve + + + + v e

D I S C U S S I O N

The results so far obtained are insufficient for conclusions to be drawn, but observations made in respect of the flea extract can be commented on. Although the extract used was very crude, yet over 73% of dogs with clinical flea hyper- sensitivity submitted for examination reacted positively. Further, of seventeen apparently normal dogs tested with flea extract only one gave a positive skin reac- tion: this and several others in the group harboured fleas. Close examination of the dorsal shoulder region of the reacting dog revealed the typical papules associated with early flea hypersensitivity. I t would appear, therefore, that the test is capable of distinguishing between non-sensitized and sensitized dogs.

I t is known that the allergen involved in flea hypersensitivity is present in flea saliva and that it has common characteritics for the three most important species infesting dogs (dog, cat and human fleas). I t is also known to be an incomplete allergen and to require conjugation with dermal collagen before being capable of stimulating an antibody response.

I t is suggested that the results from the series reported here warrant further research using a pure extract to determine skin sensitivity in flea hypersensitivity. A positive skin reaction is a useful sign to an owner of the involvement of fleas with his animal’s condition. Difficulty is often experienced in convincing an owner that fleas cause dermatitis; in fact they are the most common cause of allergic derma- titis.

Using both prick and intradermal tests, little reaction was observed in normal dog skin to a wide range of allergens. This is in marked contrast to the finding of Pomeroy (1934). However, the present author used standard modern intradermal test solutions which were considerably more dilute than the solutions used by Pomeroy .

The number of dogs with atopic dermatitis used in this series was small. Positive reactions were obtained predominantly to inhalant allergens, though two dogs -

were positive to milk. However, neither showed systemic reactions when placed on a milk-fi-ee diet for 1 week, then fed milk. Of nine dogs giving positive reactions to inhalants (house dust and kapok) four showed marked improvement on being

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D I A G N O S I S O F S K I N D I S E A S E 451

housed in kennels, but three of them showed exacerbation of hypersensitivity on being returned home and fed on the same kennel diet. This possibly indicated that their clinical signs, non-seasonal lachrymation, nasal discharge and erythema of the skin, were a result of sensitivity to inhaled allergens to which they were no longer exposed in kennels. I t is considered however that the results are insufficient numerically for other conclusions to be drawn.

Collins (1966) considers that skin testing in dogs is more applicable to the diagnosis of inhalant allergy than to ingestion allergy; his view is apparently based on the findings of Pomeroy who used very concentrated food extracts, and on the undocumented observations of others. Among twenty-two dogs with atopic dermatitis in North America, Baker (1966) examined their reactions to dust and pollens and found a high proportion of reactors: he concluded that the tests were of value in determining in which season an animal is most likely to be most severely affected.

The virtual absence of skin reaction to foods in the present small series was not surprising in view of Walton’s (1967) estimate that only 1 % of cases of canine dermatitis presented for examination showed reaction to ingested allergens.

Non-reactivity of the skin to histamine after corticosteroid therapy merely indicates the need to withdraw such therapy for some time prior to skin testing and this is especially to be remembered when the depot long-acting corticosteroids are being used. The importance of this observation is further shown by the non- reactivity of the skin, for some considerable time after corticosteroid therapy, of a flea hypersensitive dog to an intradermal flea extract.

REFERENCES BAKER, E. (1966) J . Am. vet. med. Ass. 148, 1160. BURNS, P.W. (1933) 3. Am. vet. m d . Ass. 83, 627. COLLINS, D.R. (1966) Med. Vet. 61, 679. POMEROY, B.S. (1934) Cornell Vet. 24, 335. ROOK, A., WILKINSON, D.S., EBLING, F. J. (1968) Textbook of Dermatology. Blackwell Scientific

WALTON, G.S. (1966) 3. small Anim. Pract. 7, 749. WALTON, G.S. (1967) Vet. Rec. 81, 709.

Publications, Oxford.

RCsumC. Le diagnostic et le traitement de dermatoses constituent une partie importante du travail du vtttrinaire sptcialist dans le traitement d’animaux domestiques. De par la nature allergique d’un nombre considtrable de cas, leur diagnostic peut poser des problkmes. Chez l’homme, les essais dermiques pour dtterminer l’allergie sont reconnus comme facilitant le diagnostic; les vtttrinaires, toutefois, n’y ont pas souvent recours et rares sont les rbultats publits dans ce domaine. Cette communication est un rapport prCliminaire des rbultats qu’ont fournis les essais dermiques en usant des allerghes chez des chiens normaux et ailergiques. On estime que la mtthode a de la valeur en ce sens qu’elle aide B ttablir le diagnostic de l’hypersensibilitt aux puce, mais que les rbultats prCliminaires avec d’autres allergknes sont peu concluants.

Zusammenfassung. Die Diagnose und die Behandlung von Hautkrankheiten stellen einen

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452 K . P. B A K E R

grossen Teil der Arbeit des praktkchen Tierarztes dar. Eine nicht unbedeutende Zahl von Fallen wird allergischer Natur sein und kann diagnostische Schwierigkeiten bieten. Beim Menschen ist die Priifung der allergischen Reaktion der Haut ein anerkanntes Mittel der Diag- nose, das jedoch in der tierarztlichen Praxis wenig angewendet wurde, und auch Veroffentli- chungen uber die Ergebnisse sind selten. Die vorliegende Arbeit ist ein vorlaufiger Bericht uber die Ergebnisse von Hauttests unter Verwendung von Allergenen an normalen und allergischen Hunden. Man darf annehmen, dass die Methode einen Wert als diagnostisches Hilfsmittel im Falle der Uberempfindlichkeit gegen Flohe besitzt, dass die vorlaufigen Ergebnisse der Verwen- dung anderer Allergene aber nicht eindeutig sind.