Allergies – the clinical picture, diagnosis, and treatments
1. What is an allergy? 什么是过敏？
An allergy is an immunologic response to foreign substances in foods or in the environment. These substances, allergens, are usually tolerated by normal individuals. The clinical manifestations of allergies are the visible end results of the body’s response to allergens. This response is considered a form of hypersensitivity, which can cause profound discomfort for animals and serious angst for owners. 过敏是一种对食物中或环境中外来物质的免疫反应。这些物质，过敏原通常可以被正常动物耐受。临床上所见的过敏是可见的身体对过敏原反映的最终结果。这种反映被认为是一种超敏反应，这种反应能造成动物的严重不适以及宠物主人的严重焦虑。
2. What are the signs of an allergy? 过敏的症状有哪些？
- Itching (pruritus—not spelled “pruritis”… there is no “–itis” of the “pru”.) Recognize that licking, scratching, and chewing are all possible signs of itching.
- Redness (erythema)- commonly of the skin of ears, axillae, groin, belly, and feet.
- Infections- either of the skin or the ears. Infections are commonly thought to be secondary to skin inflammation and self-trauma. In fact, allergic dogs often have a poor skin barrier to protect them from elements and commensal (normal resident) bacteria and yeast. Increased trans-epidermal water loss is a manifestation of this inadequate skin barrier function. In animals with recurrent infections, one must consider an underlying allergy as a potential cause.
- Fur mowing: The symmetrical barbering of the fur on belly, flanks, or limbs. Usually, these cats do not traumatize the skin itself.
- Eosinophilic granuloma complex: This category includes eosinophilic (often linear) granulomas, plaques, and indolent ulcers.
- Miliary dermatitis: A term applied to a “cutaneous reaction pattern” that has many possible causes including flea-bite hypersensitivity, ringworm, staphylococcal folliculitis, and allergies. The term describes multiple small crusted papules that spontaneously develop on the skin. These are often felt as the client pets the cat. Early on, without secondary infections or other trauma, these lesions are impossible for the cat to create itself. Cytology (which is often difficult to achieve) often reveals numerous eosinophils.
- Symmetrical pruritus: This is often seen as the cat that creates significant lesions on the face and neck. Secondary infection is common in this form of allergies.
- Atopics usually start off with a seasonal pruritus, but 80% of atopics develop a year round disease. This makes sense since they are pre-programmed to become allergic to their environment.
- Atopy gets worse in time, and dogs/cats do not outgrow their allergies. 遗传性过敏会随着时间变得更加严重，并且狗/猫无法压制过敏。
- Common dog breeds: Labs, Goldens, Pitbulls, Bichons, Shih-Tzus, Jack Russells, Westies, Shar-Peis, Shepherds, Spaniels, etc… And, mongrel dogs too.
- Age of onset: Dogs usually 1-3 years of age. Generally, signs start no later than 6 years old in dogs. Cats can “start” with signs a little later in life-- 1-8 years old.
- Atopics will respond to appropriate steroid dosages (dogs: 1 mg/kg prednisolone daily) if there is not concurrent infection, food allergy, or ectoparasitism (fleas, scabies, cheyletiellosis).
- Atopy is often strongly suggested by a history with a seasonal pruritus. However, it should be a diagnosis of exclusion and we only allergy test once we know the diagnosis of atopy.
- Allergens incite atopic dermatitis transdermally, orally, and maybe via inhalation. The transdermal component is important as dogs and cats live on the ground and do not wear shoes, etc…
- Food allergens are usually proteins or glycoproteins in foods. Common allergens are meats, wheat, corn, soy, dairy. However, theoretically anything ingested can be a food allergen.
- An animal must eat the inciting allergen for some time before developing an allergy. Many clients say “he has eaten the same food for years, he can’t be allergic to it”. This is actually a necessary scenario and dogs/cats can develop food allergens at any point in life for no apparent reason.
- Food allergens must be considered in a year-round itchy dog/cat that develops signs later in life. As previously mentioned, atopy is a genetic condition and the signs start in relatively young adults. Atopy does not start late in life.
- Food allergies may or may not respond to appropriate dosages of steroids. Since uncomplicated atopy will respond to steroids, we must consider a food allergy in a dog that does not respond.
- There are no reliable blood tests for food allergies. Serologic tests looking for IgE against food allergens are inaccurate and even misleading.
- A properly performed home cooked elimination diet trial is the only 100% accurate “test”. These are designed once we know the current or previously eaten ingredients. Food allergics should improve within 4 weeks of removing the inciting ingredient. However, it may take 12 weeks to see maximal benefit since the allergic immune system takes time to normalize.
- Commercially available “novel protein” or “hydrolyzed” (chemically chopped up into smaller pieces) diets have a 10-15% failure rate. This is true even if the bagged diet is chosen based on current/previous ingredients. Ingredients get pretty similar as you look down the list (fish oil, pork fat, etc…).
- Watch out for terms like “animal digest” or “meat-by-product” or “fish-meal.”
- Thankfully, dogs and cats very rarely develop allergies against an effective novel protein diet.
- Shampoos: Appropriate high quality shampoos increase the hydration of the stratum corneum (outer skin layer) and improve the skin barrier. Shampoos are a very effective vehicle for antimicrobial agents. Shampoos can contain anti-pruritic agents (colloidal oatmeal, hydrocortisone, pramoxine, etc…). Shampoos also help remove topical allergens through a simple cleaning action. Shampoos are obviously not a great option for cats.
- Antihistamines (and other nonsteroidal agents): Antihistamines can reduce the action of histamine on a receptor level (H1) and reduce the release the histamine. They are better at preventing pruritus and are not good at removing pruritus. As such, we commonly use steroids to “put out the fire” and then we can see if the antihistamine can keep the animal comfortable. If they help, then they are given routinely at the appropriate dosage interval. Antihistamines can have a steroid sparing effect and they are often used together. Nonsedating antihistamines (Claritin, Seldane, etc…) are not as effective as the sedating types (deiphenhydramine, chlorpheniramine, hydroyzine, clemastine). Amitriptylline (a Tri-Cyclic Antidepressant) has potent antihistaminic properties, is cheap, administered twice daily, and may help dogs with anxiety. Pentoxifyline ( a methylxanthine derivative) works in a different manner but helps up to 30% of atopics. Antihistamines can be very effective in cats.
- Omega Fatty Acids: Certain omega fatty acids can lead to anti-inflammatory prostaglandins and leukotrienes. To achieve this result, the ratio of Omega 6’s (e.g. certain vegetable oils) to Omega 3’s (e.g. fish oils) is very important and should be between 10:1 or 5:1. Supplements (DermCaps®, etc…)can help to achieve this goal, but it is easier/cheaper to have a diet with the ideal types/quantity/ratio of omega FA’s. Eukanuba® dog foods have been studied repeatedly and have consistent and high quality omega FA’s.
- Steroids: We use short acting steroids (pred family) when necessary to control itching. Prednisolone is ideal for cats and we often use this over plain prednisone in dogs too. We do not want to use more than 0.5 mg/kg prednisolone every other day long term as it has many side effects (Cushings, elevated liver enzymes, immunosuppression, polyuria/polydipsia). Methylprednisolone is 20% more potent than prednisolone, but has minimal mineralocorticoid properties and is well tolerated by older patients. DepoMedrol (methylprednisolone acetate) is a reasonable option for cats that are difficult to pill. The shots can last over 2 months, but should not be used as a sole treatment for atopy if more than 2-3 shots are needed annually.
- Cyclosporine (Atopica®): A very expensive option when needed every day (about $8-9 for the average Labrador!). Perhaps 70% of animals improve when dosed daily. This 70% is not completely “cured” and may only have less erythema or partial improvement in pruritus. If daily therapy works, then we try to go to every other or even every third day. With each drop in frequency, you can expect to lose control in ½ the animals that improved. It is a good option for cats (due to efficacy and cost reasons), BUT… they must be Toxoplasma gondii titer negative or they may develop fulminant toxoplasmosis and die.
- What about allergy shots?.... 那么脱敏针呢？
- Allergy testing is available as serologic and intradermal skin test (IDST) options. Both have pro’s and con’s. (No steroids allowed for either testing scheme. Sedation only needed with IDST. Antihistamines and omega fatty acids ok for serology).
- Serologic allergy testing (VARL, HESKA, Greer) looks at species specific IgE’s against environmental allergens. False positives or negatives are possible as blood antibodies may not correlate with the antibodies in the skin. Allergy shots based on serology can work in 2/3 of dogs, and this is about the same success rate as allergy shots based on skin testing.
- IDST should not have false positive results, but can have false negative results. Only well trained/experienced clinicians should perform/interpret IDST.
- Either serology or IDST alone can explain the itching pattern in 75% of cases. We often need to use both tests to best explain an animal’s seasonality or lack thereof. ASIT based on both tests combined may have the best results.
- ASIT is giving purified, sterile (but fairly crude) allergen extracts subcutaneously. We are giving way more of an allergen than they would normally encounter, but it is via a different route (SQ). Theoretically, this exposure should drive the Th2 response (hypersensitivity) toward a Th1 response (tolerance).
- Initially, a dilute and small quantity is given, and then shot gradually build up to more concentrated and more volume of shot.
- The most common side effect is increased itching, and this usually indicates that we are giving too much allergen (at least once at a maintenance dosage).
- A common scenario is that the shots provide a palliative effect, but this wears off before the next shot is due. This indicates that the interval may need to be shorter.
- Shots make 1/3 dogs great on shots alone, 1/3 dogs better (still need medicines, but generally need less steroids), and just do not work in 1/3 of dogs.
- It takes a full year to see maximal benefit from the shots.
NOTE: The hallmarks of allergic dogs are the above signs without primary skin lesions. In other words, by definition, they commonly have an “itch that rashes” and not a “rash that itches”. However, the latter scenario must be ruled out and addressed as skin infections (yeast or bacterial) often exacerbate pruritus.
CATS: Four common presentations of cat allergies.
1. What is atopy? 什么是遗传性过敏？
Atopy is generally defined as a genetically pre-programmed condition that promotes the development of antibodies (IgE, IgGd) against normally innocuous environmental allergens (pollens, dusts, danders, mites), and the subsequent cutaneous signs (redness, itching) upon exposure to those allergens.
T-lymphocytes are essential in the regulation of the immune system. Helper-T cells have different roles and produce different cytokines. Th-1 cells generally promote tolerance, whereas Th-2 cells are thought to promote hypersensitivity reactions (typified by production of IgE). Atopic animals have an imbalance in this system, and this is a hotbed of current research.
2. Food allergies? What’s the deal? 食物过敏? 是什么?
The signs of food allergies or atopy can be very similar. Also, both conditions can be present in probably 10-20% of allergic pets. As such, if an animal has signs of an allergy that is at least partially present at all times of the year, then a food allergy should be ruled out. Food allergies must be considered in an animal that is itchy very young in life (< 4-6 months). This makes sense since the immune system of an atopic takes some time before it can develop an allergy to the environment—at least 6 months, but usually 1-2 years. Young animals often have internal parasites or viral GI diseases that promote a “leaky” gut mucosal barrier.
食物过敏或遗传性过敏的症状可能非常相似。并且，在10-20%的过敏的猫中，两种情况都可能表现。这样，如果动物过敏的症状在全年至少有部分表现，那么可以排除食物过敏。对于动物在年轻时（<4-6个月）开始发痒， 那么食物过敏应給予认真考虑。这是有道理的，因为遗传性过敏的免疫系统需要一些时间去对环境产生过敏反应—至少6个月， 但通常1-2年。年轻的动物通常有体内寄生虫或病毒性肠胃疾病促进“渗漏”的肠子产生一层粘液性的屏障。
3. Atopy Treatment Options: 遗传性过敏治疗选择：
Treating atopic animals often requires a multi-faceted approach. The goal of all therapies is to achieve a level of “tolerable” itch and/or reduce the secondary infections. Tolerable is a relative term and is different for certain animals and certain clients. A Bichon may have a lower threshold and more severe symptoms than a Labrador. We can remove all pruritus with higher dosages of steroids, but this is not compatible with a long healthy life. If we need to use steroids, we strive to achieve the lowest dose possible on no more than an alternate day basis. 治疗遗传性过敏动物通常需要多方面的手段。所有疗法的目标是达到一种“可忍受的”痒和/或减少后续感染的水平。可忍受的是一个相对的名词并且对以某些动物和客人会难定义。一直比熊与一只拉布拉多相比可能会对痒较不敏感但却病得更严重。我们用较大剂量的类固醇去除所有搔痒，但这对长期的身体健康不利。如果我们需要使用类固醇，我们应经可能的使用最小剂量，不多于隔日使用。
抗组胺剂（以及其他非固醇类药物）：抗组胺剂可以降低组氨酸对H1受体水平的作用并且降低组氨酸的释放。它们的优势在于预防搔痒而不是祛除瘙痒。这样，我们通常用类固醇去“灭火”，然后使用抗组胺剂看是否能让动物保持舒适。如果它们有作用，可以将它们作为常规药在适当的剂量间隔给药。抗组胺剂有对类固醇的补给作用并且它们可以被同时使用。非镇静型抗组织胺剂（克敏能,特非那丁,等等...）不如镇静型有效（deiphenhydramine, chlorpheniramine, hydroyzine, clemastine）。阿米替林（一种三环抗忧郁剂）有强抗组胺酸的性质，很便宜，每日两次，并且可能帮助狗的焦躁症。己酮可可碱（一种甲基黄嘌呤衍生物）通过一种不同的方式发挥作用但可以帮助缓解30%的遗传性过敏）。抗组胺剂对猫非常有效。
4. Allergy testing and allergen specific immunotherapy (ASIT or “allergy shots”): 过敏测试以及过敏原特异性免疫疗法（ASIT或“脱敏针”）。
血清学过敏测试（VARL, HESKA, Greer）检测物种特异性IgE所抗的环境抗原。假阳或假阴在血液抗体与皮肤抗体不符是可能出现。依据血清学结果的脱敏针对2/3的狗起作用，这个成功几率与皮试为依据的脱敏针大致相同。
- If shots work, they are given for life.
Our collective goal is to achieve a level of tolerable pruritus, while using little to know steroids. In the allergic pets that we see, we sometimes find the pet needs steroids long term. In this case, we strive to use the lowest dosage possible—meaning the least we need on an alternate day basis to keep them comfortable. 我们的总体目标是把将搔痒症控制在可忍受的程度，同时尽量少的使用类固醇。在我看过的过敏的宠物中，我们通常需要长期使用类固醇。既然这样，我们就需要尽可能降低剂量-至少我们需要在隔天的基础上以确保它们舒适。
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