INFORMATION FOR VETS
Dear Colleague,
Not all skin cases are difficult. Some respond well to rational treatments. However, because allergy is incurable, many on-going cases of pruritus need further workup to establish the cause of the hypersensitivity. Intradermal testing is still considered the “gold standard” diagnostic test in the work up for canine atopic dermatosis. Other skin cases just don’t go according to plan, not all animals have “read the book” so they don’t present in a typical fashion. For these atypical cases, or ones which don’t seem to make any sense, it is almost always worthwhile having another brain on the case, even if it is just to bounce ideas off.
If you feel that a dermatological case isn’t going well, or if you have a presumed hypersensitivity case that needs further work up, I am very happy to be involved. The referral system is easy. You simply send us the clinical notes and the client email and we will do the rest. Although I appreciate referral letters, they are a job that you can probably do without, and the clinical notes are more important. Highlighting the important or relevant appointments is helpful.
We will send out an confirming the animal’s appointment time, giving directions on how to find the hosting clinic, and a history form for the client to fill out before the referral consultation, giving their version of the case.
After the initial or follow-up consultations, I usually have a referral letter to your practice within a week. If you can supply a contact email address and the name of the veterinarian to whom the letter should go, so much the better. It is not always possible to get the animal off corticosteroids before they see me. That is fine. I would rather see them and judge at the consultation the best way to reduce and then stop the corticosteroids. Obviously now that we have both Oclacitinib and Lokivetmab available, corticosteroids are much less of a problem.
The chart below gives the withdrawal times for various medications before intradermal testing.
Not all skin cases are difficult. Some respond well to rational treatments. However, because allergy is incurable, many on-going cases of pruritus need further workup to establish the cause of the hypersensitivity. Intradermal testing is still considered the “gold standard” diagnostic test in the work up for canine atopic dermatosis. Other skin cases just don’t go according to plan, not all animals have “read the book” so they don’t present in a typical fashion. For these atypical cases, or ones which don’t seem to make any sense, it is almost always worthwhile having another brain on the case, even if it is just to bounce ideas off.
If you feel that a dermatological case isn’t going well, or if you have a presumed hypersensitivity case that needs further work up, I am very happy to be involved. The referral system is easy. You simply send us the clinical notes and the client email and we will do the rest. Although I appreciate referral letters, they are a job that you can probably do without, and the clinical notes are more important. Highlighting the important or relevant appointments is helpful.
We will send out an confirming the animal’s appointment time, giving directions on how to find the hosting clinic, and a history form for the client to fill out before the referral consultation, giving their version of the case.
After the initial or follow-up consultations, I usually have a referral letter to your practice within a week. If you can supply a contact email address and the name of the veterinarian to whom the letter should go, so much the better. It is not always possible to get the animal off corticosteroids before they see me. That is fine. I would rather see them and judge at the consultation the best way to reduce and then stop the corticosteroids. Obviously now that we have both Oclacitinib and Lokivetmab available, corticosteroids are much less of a problem.
The chart below gives the withdrawal times for various medications before intradermal testing.
GUIDE FOR INTRADERMAL SKIN TEST PREPARATION
1. Discontinue all drugs which interfere with intradermal skin testing.
Drug
Tranquilizers Topical steroids – ear, eye or skin Antihistamines Prednisone Triamcinolone/Depredone/Vetacortyl Cortavance Cyclosporine Apoquel Cytopoint |
Withdrawal Time
2 days 10 days 10 days 4 weeks 10 weeks 10 days No withdrawal Prefer 2 days No withdrawal |
2. Control Pyoderma
3. Pursue Food Allergy with an elimination diet
1. Royal Canin Hypoallergenic or Anallergenic, or Hills Z/D Ultra.
2. A Fish and rice, fish and potatoes or horsemeat and rice. Home cooked diets are less
desirable. NB animals may lose weight so you may need to feed more.
4. Ruleout Sarcoptes
1.A. 5% Lime Sulphur dips at 5-7 day intervals for three weeks.
1.B Revolution (selamectin) applied fortnightly for 3 times.
1.C. Trial with NexGard (afoxolaner), Bravecto (fluralaner) or Simparica (sarolaner).
5. Symptomatic therapy
1.A Cool Water Bathing
-Colloidal Oatmeal Rinse
1. B Barrier methods
-Elizabethan collars
-Foot Wraps/socks
-Hobbles
-T-shirts
- Appropriate “skin antibiotics” for example Cephalosporins
- Antibacterial shampooing weekly
3. Pursue Food Allergy with an elimination diet
1. Royal Canin Hypoallergenic or Anallergenic, or Hills Z/D Ultra.
2. A Fish and rice, fish and potatoes or horsemeat and rice. Home cooked diets are less
desirable. NB animals may lose weight so you may need to feed more.
4. Ruleout Sarcoptes
1.A. 5% Lime Sulphur dips at 5-7 day intervals for three weeks.
1.B Revolution (selamectin) applied fortnightly for 3 times.
1.C. Trial with NexGard (afoxolaner), Bravecto (fluralaner) or Simparica (sarolaner).
5. Symptomatic therapy
1.A Cool Water Bathing
-Colloidal Oatmeal Rinse
1. B Barrier methods
-Elizabethan collars
-Foot Wraps/socks
-Hobbles
-T-shirts
Testing Day
The owner will withhold food from 10pm the night before unless the appointment is late in the day. In that case, an early light breakfast is appropriate. There is no need to restrict water except for the last several hours before the appointment.
Testing procedure
The animal will be sedated and a patch (approximately 15 x 10 cm) shaved on the lateral left chest. Approximately 40 – 50 intradermal injections will be administered and “read” 15 minutes later. A Tradescantia fluminensis (Wandering Jew or Wandering Willie) patch test may be performed in the inguinal area. Hypersensitivity to Tradescantia is a type 4 delayed reaction, so this test will be read at home, by the owner.
Reading the intradermal test
Saline is the negative control, this reaction is assigned a “0” value. Histamine is the positive control with an assigned value of “4”. All reactions area assigned values ranging from 0-4. Antigen reactions of 2+ or greater are considered significant.
D. pteronyssinus and D. farinae – These two house dust mite allergens are tested at two strengths (100 and 25 pnu) and both reactions are reported. For example if D.farinae is reported to be 4/4, then that means that it had strong positives at both concentrations. If the reaction is reported as 3+/1, it had a moderately strong reaction at the higher concentration, but a weak reaction at the diluted strength.
Acarus siro and Tyrophagus putrescentiae are free living storage mites that are commonly found in dry pet food.
Note: this is an idealized protocol. It is not necessary to ruleout all of the above. Some owners really appreciate being referred early and since I have to do many of the tests for myself, there is a certain amount of doubling up which early referral avoids. If you have a case that completely satisfies the criteria for canine atopic dermatitis, using Favrot’s criteria: as discussed in Canine Atopic Dermatitis: An Overview and Historical Perspective Richard E.W. Halliwell, 2012 Symposium Proceedings • Allergic Skin Disease:
The owner will withhold food from 10pm the night before unless the appointment is late in the day. In that case, an early light breakfast is appropriate. There is no need to restrict water except for the last several hours before the appointment.
Testing procedure
The animal will be sedated and a patch (approximately 15 x 10 cm) shaved on the lateral left chest. Approximately 40 – 50 intradermal injections will be administered and “read” 15 minutes later. A Tradescantia fluminensis (Wandering Jew or Wandering Willie) patch test may be performed in the inguinal area. Hypersensitivity to Tradescantia is a type 4 delayed reaction, so this test will be read at home, by the owner.
Reading the intradermal test
Saline is the negative control, this reaction is assigned a “0” value. Histamine is the positive control with an assigned value of “4”. All reactions area assigned values ranging from 0-4. Antigen reactions of 2+ or greater are considered significant.
D. pteronyssinus and D. farinae – These two house dust mite allergens are tested at two strengths (100 and 25 pnu) and both reactions are reported. For example if D.farinae is reported to be 4/4, then that means that it had strong positives at both concentrations. If the reaction is reported as 3+/1, it had a moderately strong reaction at the higher concentration, but a weak reaction at the diluted strength.
Acarus siro and Tyrophagus putrescentiae are free living storage mites that are commonly found in dry pet food.
Note: this is an idealized protocol. It is not necessary to ruleout all of the above. Some owners really appreciate being referred early and since I have to do many of the tests for myself, there is a certain amount of doubling up which early referral avoids. If you have a case that completely satisfies the criteria for canine atopic dermatitis, using Favrot’s criteria: as discussed in Canine Atopic Dermatitis: An Overview and Historical Perspective Richard E.W. Halliwell, 2012 Symposium Proceedings • Allergic Skin Disease:
Set 1
Age at onset < 3 years Mostly indoor Corticosteroid responsive pruritus Chronic or recurrent yeast infections Affected front feet Affected ear pinnae Non-affected ear margins Non-affected dorso-lumbar area |
Set 2
Age at onset < 3 years Mostly indoor Pruritus sine materia at onset Affected front feet Affected ear pinnae Non-affected ear margins Non-affected dorso-lumbar area |
Using the first set of criteria, when five were satisfied, the sensitivity was 0.854 and the specificity was 0.791, and with six satisfied the corresponding data were 0.582 and 0.885. Using Set 2, with five criteria the sensitivity was 0.772 and the specificity 0.83, and with six satisfied the data were 0.42 and 0.937. Obviously, whichever parameters are used, the results are far from perfect. One must also bear in mind that the development of diagnostic criteria is a somewhat circular exercise, in that it employs clinical cases upon which a diagnosis has been made by a wide range of clinicians employing varying techniques. Suffice it to say that a very many experienced clinical veterinary dermatologists make the diagnosis by 1) observation of compatible clinical signs and 2) failure to document any other explanation for these clinical signs.
And if the animal is a breed that is predisposed:
Breed Predilections
Breed predilections have long been recognized, and the mode of inheritance is currently under investigation. Those breeds shown to be significantly predisposed in two recent studies were Labrador retriever, Golden retriever, West Highland White terrier, Chinese shar-pei, Bull terrier, Bichon frisé, Tibetan terrier, English springer, Boxer, French bulldog, Dalmatian, Hungarian Vizsla, and Basset hound.
Then you may want to give the owner the option of early referral. In my experience, many owners appreciate being given the option early rather than at the end of a long and tedious work up.
And if the animal is a breed that is predisposed:
Breed Predilections
Breed predilections have long been recognized, and the mode of inheritance is currently under investigation. Those breeds shown to be significantly predisposed in two recent studies were Labrador retriever, Golden retriever, West Highland White terrier, Chinese shar-pei, Bull terrier, Bichon frisé, Tibetan terrier, English springer, Boxer, French bulldog, Dalmatian, Hungarian Vizsla, and Basset hound.
Then you may want to give the owner the option of early referral. In my experience, many owners appreciate being given the option early rather than at the end of a long and tedious work up.
This German shepherd had a very positive intradermal test to most
tree, grass and weed pollens. We number left to right, starting in the upper left hand corner with number 1 which is saline, number 2 and 47 are saline. Interestingly this dog had no reactions to 38 (flea), 39, 40 (2 dilutions of D. pteronyssinus), 41 or 42 (2 dilutions of D. farinae). |
This three year old female Labrador with ear and pedal pruritus had
an intradermal with good positive controls (histamine 2 and 47) and very positive reactions to D.farinae, 4 at both dilutions of the antigen (41 & 42), both storage mites Acarus siro and Tyrophagus putrescentiae (45 7 46) and Malassezia (44). Intradermal tests that are strongly positive for D.farinae and both storage mites are the most common of the tests. |
The Clinician’s Guide to Interpreting Dermatology Referral Letters
A number of colleagues have found the dermatological referral letters too terse, or too technical to be completely useful. Often, given time constraints, it is not possible to go into full detail about a case. I have prepared the following guide in an effort to rectify those problems and to make referral letters more understandable.
Chief complaint: At the first visit this is usually a summary of what the client sees to be the main reason for the visit. At the revisit, it may be the client’s summary or it may be the established diagnosis.
History: I try to follow the normal dermatological history taking ideal by finding out the time of onset, whether the condition is seasonal, how pruritic or not it is, whether flea control is used, what other pets are in the household, and whether the animal is mainly inside or outside. I try to establish what drugs were used, whether the animal responded or not, and try to establish if the dose rates were optimal. In your summaries if you could include the animal’s weight and the actual mg. of medication prescribed it would be useful. A good response to antibiotics indicates a pyoderma. A good response to corticosteroids alone is suggestive of hypersensitivity. A good response to an anti-fungal (usually itraconazole, terbinafine or fluconazole) alone is suggestive that Malassezial overgrowth is an important component You can see why it is important to use one medication at a time, so that each response or non-response tells you something about the aetiology of the skin condition.
Physical examination: most of this is self evident.
Assessment: this is equivalent to the differential diagnoses. Rule outs are differentials that we need to disprove by further testing.
Diagnostic Plan: Cytology is nearly always done, usually by direct skin impression smear and then stained with diff quik. In dry or hard to get at areas, I will do a cello tape impression smear. Cytology is read on the spot.
The intradermal test (IDT) used to be called the intradermal skin test (IDST). I am now using 45 antigens from Greer Labs in the USA. My most recent introductions are Malassezia (yeast) and the free living storage mites, Acarus siro and Tyrophagus putrescentiae. The negative control is diluent or saline and is arbitrarily called a 0. The positive control is histamine at 1: 100,000 and is arbitrarily termed 4. All reactions are graded at 15 minutes in relation to the controls, using a scale of 0 to 4. Dermatophagoides farinae (D.farinae) and to a lesser extent Dermatophagoides pteronyssinus (D. pteronyssinus) are the two most common reactions in dogs and cats (and NZ humans). These house dust mites are tested at two differing concentrations, 100 pnu and 25 pnu, and I used to report their positive reactions as 4/4 if there was a very strong reaction. I now report them separately. We generally regard reactions >2 to be significant. Thus if I report a skin test to be macrocarpa 4, plantain as -3, and D.farinae as 3/1 (or now 100pnu 3, 25pnu 1 in the new system) the interpretation would be a very strong reaction to macrocarpa, a less strong but still significant reaction to plantain, and a wishy washy response to a house dust mite. I would then use the clinical history to interpret this response. If there was year round pruritus, and I had ruled out other causes, I might consider the D.farinae to be significant. I would be happy to email a copy of my intradermal testing sheet to anyone interested.
Elimination diet: In one retrospective study, of food allergic animals, 36% had concurrent food and flea hypersensitivity, 26% had food and inhaled, and 22% had food, flea and inhaled. Working the other way, just because a dog has a positive skin test, it doesn’t mean he can’t be food allergic.
Patch testing for Tradescantia fluminensis (Wandering Willie) hypersensitivity is often done in conjunction with the intradermal test. Because it is a delayed type IV hypersensitivity, the results of the test must be read at home by the owner at three hourly intervals. Most reactions take place by 6 to 12 hours.
Treatment Plan: The hosting clinic usually supplies the initial medications that I prescribe, and then either the future prescriptions are provided by their normal general practice veterinary centre or if my input is needed on an on-going basis, I provide the medications. The medications should never be supplied by the hosting clinic on an on-going basis.
Management Plan: When a dog is house dust allergic, I often suggest lifestyle number of changes – staying out of bedrooms, off beds and couches- that can be done easily, and others that are more difficult such as staying outside more. If these life style changes give only minimal relief, the next rational step would be immunotherapy. Although it is not always successful (see the hand out on immunotherapy on the Advice sheets pick list), immunotherapy offers the best way of managing atopic dogs.
A number of colleagues have found the dermatological referral letters too terse, or too technical to be completely useful. Often, given time constraints, it is not possible to go into full detail about a case. I have prepared the following guide in an effort to rectify those problems and to make referral letters more understandable.
Chief complaint: At the first visit this is usually a summary of what the client sees to be the main reason for the visit. At the revisit, it may be the client’s summary or it may be the established diagnosis.
History: I try to follow the normal dermatological history taking ideal by finding out the time of onset, whether the condition is seasonal, how pruritic or not it is, whether flea control is used, what other pets are in the household, and whether the animal is mainly inside or outside. I try to establish what drugs were used, whether the animal responded or not, and try to establish if the dose rates were optimal. In your summaries if you could include the animal’s weight and the actual mg. of medication prescribed it would be useful. A good response to antibiotics indicates a pyoderma. A good response to corticosteroids alone is suggestive of hypersensitivity. A good response to an anti-fungal (usually itraconazole, terbinafine or fluconazole) alone is suggestive that Malassezial overgrowth is an important component You can see why it is important to use one medication at a time, so that each response or non-response tells you something about the aetiology of the skin condition.
Physical examination: most of this is self evident.
Assessment: this is equivalent to the differential diagnoses. Rule outs are differentials that we need to disprove by further testing.
Diagnostic Plan: Cytology is nearly always done, usually by direct skin impression smear and then stained with diff quik. In dry or hard to get at areas, I will do a cello tape impression smear. Cytology is read on the spot.
The intradermal test (IDT) used to be called the intradermal skin test (IDST). I am now using 45 antigens from Greer Labs in the USA. My most recent introductions are Malassezia (yeast) and the free living storage mites, Acarus siro and Tyrophagus putrescentiae. The negative control is diluent or saline and is arbitrarily called a 0. The positive control is histamine at 1: 100,000 and is arbitrarily termed 4. All reactions are graded at 15 minutes in relation to the controls, using a scale of 0 to 4. Dermatophagoides farinae (D.farinae) and to a lesser extent Dermatophagoides pteronyssinus (D. pteronyssinus) are the two most common reactions in dogs and cats (and NZ humans). These house dust mites are tested at two differing concentrations, 100 pnu and 25 pnu, and I used to report their positive reactions as 4/4 if there was a very strong reaction. I now report them separately. We generally regard reactions >2 to be significant. Thus if I report a skin test to be macrocarpa 4, plantain as -3, and D.farinae as 3/1 (or now 100pnu 3, 25pnu 1 in the new system) the interpretation would be a very strong reaction to macrocarpa, a less strong but still significant reaction to plantain, and a wishy washy response to a house dust mite. I would then use the clinical history to interpret this response. If there was year round pruritus, and I had ruled out other causes, I might consider the D.farinae to be significant. I would be happy to email a copy of my intradermal testing sheet to anyone interested.
Elimination diet: In one retrospective study, of food allergic animals, 36% had concurrent food and flea hypersensitivity, 26% had food and inhaled, and 22% had food, flea and inhaled. Working the other way, just because a dog has a positive skin test, it doesn’t mean he can’t be food allergic.
Patch testing for Tradescantia fluminensis (Wandering Willie) hypersensitivity is often done in conjunction with the intradermal test. Because it is a delayed type IV hypersensitivity, the results of the test must be read at home by the owner at three hourly intervals. Most reactions take place by 6 to 12 hours.
Treatment Plan: The hosting clinic usually supplies the initial medications that I prescribe, and then either the future prescriptions are provided by their normal general practice veterinary centre or if my input is needed on an on-going basis, I provide the medications. The medications should never be supplied by the hosting clinic on an on-going basis.
Management Plan: When a dog is house dust allergic, I often suggest lifestyle number of changes – staying out of bedrooms, off beds and couches- that can be done easily, and others that are more difficult such as staying outside more. If these life style changes give only minimal relief, the next rational step would be immunotherapy. Although it is not always successful (see the hand out on immunotherapy on the Advice sheets pick list), immunotherapy offers the best way of managing atopic dogs.