Autoimmune and Immune mediated skin diseases Flashcards
Autoimmune, immune mediated,
When investigating a pruritic dog, in what order should which investigations take place?
1: Investigate cause of pruritus e.g. Malassezia dermatitis
2: Investigate potential underlying causes for this e.g. ectoparasites, environmental atopy, food atopy, endocrinopathy, immune mediated
3: If no ectoparasites found, carry out diet exclusion trial to rule in/out food atopy
4: If ineffective, and have ruled out all other causes, can diagnose as environmental atopy
5: Can investigate specific allergen or choose not to and control clinical signs
Describe the options for carrying out a food exclusion trial
- home cooked using novel proteins e.g. white fish, pork, rabbit etc., restricted to single protein source, single carbohydrate source and water. Start at 150% of original commercial diet, increase if weight loss. Minimum 3, up to 10 weeks
- OR commercial diets containing novel or hydrolysed proteins. Minimum 8 weeks. If no response try home cooked
What are the 2 methods for investigating allergens?
Intradermal allergy testing and serological tests
How does intradermal allergy testing work?
- shows type 1 hypersensitivities
- Tests capacity of skin to react to allergens
Discuss the disadvanages of intradermal allergy testing
- Time consuming
- Requires clipping and sedation
- Cannot be performed in lichenified, hyperpigmented, inflamed skin, widespread pyoderma or seborrhoea
- Allergens may be expensive to obtain
- Rare risk of anaphylaxis
- Harder in cats
Describe the method for intradermal allergy testing
- Introduce allergen into skin of animal, mark location on a sheet
- Measure degree of swelling, indicating inflammation and therefore allergic reaction to allergen to identify if reaction has occurred indicating allergy
How does serology testing for allergy work?
- Measure serum IgE alone, but may not correlate to levels in the skin
Compare the variations of serology testing for allergens
- Polyclonal: may measure trace IgG and give false positives
- Monoclonal: less sensitive, false negatives
- Mixed allergens: avoided as do not identify specific allergens
- Mast cell receptor molecule for specific IgE: better, but more expensive
What medical treatments are available for environmental atopy?
- Steroid creams
- Ciclosporin
- Glucocorticoids
- Lokivetmab
- Oclacitanib
- Immunotherapy/hyposensitisation
Identify actions an owner can take to avoid exposure of a dog to common allergens e.g. house dust mites
- Freeze bedding and any soft toys for 24 hours after washing
- Do not allow dogs in bedroom
- Hypoallergenic mattress and pillow covers for human bedding
- Wash human and dog bedding >70degressC
- Anti-dust mite sprays
- Remove carpets
- Socks for going on walks
Describe the immunotherapy/hyposensitisation protocol for an allergy
- Shots recommended if allergic to pollens, dust mites
- 17 injections at 3 day intervals, last 3 at 10, 20, 30 days intervals
- then injections every 2-3 weeks for 2-3 years
- High cost
What are the differentials for a dog with erythema, alopecia, hyperpigmentation on legs, crusting, lichenification
- Mange
- Fleas
- Bacterial skin infection
- Allergy
- Mites
In a case of environmental atopy where the owner has little money available for treatment, what actions would you advise?
- Glucocorticoids (short term)
- Anti-histamines e.g. piriton
- Good ectoparasite control
- Careful management of heat, humidity and stress
- Supplement EFAs, moisturisse
- Shampoo to remove allergens in coat
- Hypoallergenic diet may help
- Steroid cream in flare up areas
Outline an example of an immune mediated skin disease of cows
- Bovine leukocyte adhesion deficiency
- Genetic, and once gene identified was bred out
- Was due to BLAD gene, which led to a replacement of cytosine by a guanosine in the CD18 gene
Give examples of primary immunodeficiency disorders of the skin in small animals
- Severe combined immunodeficiency disease (SCID)
- Lethal acrodermatitis in English bull terriers
- Defective neutrophil function in Weimaraners
- Leukocyte adhesion deficiency in Irish setters
- Canine granulocytopathy syndrome in Irish setters with juvenile bacterial pyoderma
- Canine cyclic haematopoiesis of gray Collies
- Hypotrichosis and thymic aplasia in Birman kittens
- Chediak Higashi syndrome of cats
Identify the points in the immune system where development blocks may lead to immunodeficiencies
- Lymphoid precursor dysfunction can lead to combined immunodeficiency
- Myeloid precursor defects may lead to neutrophil defects
- Issues with “Bursal” processing may lead to agammaglobulinaemia
- Issues with B cells during development can lead to deficiencies in individual immunoglobulin classes
- Thymic aplasia leads to lack of thymic processing and T cell defects
Explain what is meant by a primary immuno-deficiency condition
A genetic defect in the immune system leading to clinical disease, rare
Explain what is meant by a secondary immuno-deficiency condition
Impairment of the immune system due to factors such as viral and other infections, endogenous hormones, drugs, age and malnutrition. Leads to the development of various uncommon conditions
Identify the general mechanisms that may cause autoimmune diseases
- Normal responses that go awry or abnormal responses
- Immune dysfunction
- Genetics
- Environmental triggers
- Inflammation
- Trauma
- Infection
- Neoplasia
Give examples of ways in which a normal immune response can go awry and lead to autoimmune disease
- Immune response to previously hidden antigens, which may appear due to tissue damage, molecular alterations, or newly synthesised antigens
- Or response to molecular mimicry as a result of microbial cross reactions
Give an overview as to how an abnormal immune response may occur, leading to autoimmune disease
- Self reactive T cells and lymphoid tumours
- Failure of apoptosis, viral infections, microchimerism
- Hormonal influences, genetic predisposition
- Failure of regulatory control
Give an example how neoplasia can lead to autoimmune disease
Thymoma in cats, develop skin diseases, mechanism poorly understood, but removal of thymoma leads to resolution of skin disease
- T cells called to skin, target follicles leading to alopecia
Name the structures that act as autoantigens in the following conditions
a: Pemphigus
b: Pemphigoig
c: Linear IgA dermatitis
d: Epidermolysis bullosa acquista
a: Desmosomes
b: Hemidesmosomes
c: Lamina lucida
d: Type VII collagen fibres below the lamina densa
Which structure of the skin is a common target of immune disease and what is the result?
Desmosomes, leads to skin falling apart
Which forms of pemphigus are more, and which are less, common in dogs?
- Vulgaris rare in animals (common in people)
- Foliaceous common in dogs
- Also erthematosus more common in dogs
- Uncertain regardin vegetans
Describe the aetiology of pemphigus
- Usually unknown
- Associated wirh abnormal immune regulation or antigenic stimulation
List the factors that are recognised as causes of pemphigus in animals
- Neoplasia
- Infectious agents
- Drugs (antibiotics, vaccines, wormers)
- Chronic skin disease
- (In people: autoimmune disorders, certain haplotypes, pregnancy)
Compare the pathogenesis of pemphigus vularis and foliaceous
- Autoantibodies bind to all suprabasal layers of stratified squamous epithlium
- Desmoglein 3 mainly in lower layers (vulgaris, split near bottom of epiderms)
- Desmoglein 1 mainly in superficial layers (foliaceous, split near top)
- Desmocollin 1 is major autoantigen in canine pemhigus foliaceous
- Desmosome break apart = pustules, ulcerations
Describe the clinical signs of canine pemphigus foliaceous
- Leaf-like pustule appearance
- Erythema around pustules intense
- Sterile pus in skin
- Crusting occurs as pustule disappears
- Pyrexia, inappetance, depressed
- Lesions on face ad feet
- Pruritus is a major feature
- No response to antibactieral therapy
What is the signalment for canine pemphigus foliaceous?
- Any breed, but Cockers predisposed
- Onset from 2-7yrs
- Disease chronic in 75% of cases
Outline feline pemphigus foliaceous
- Little understood re. pathogenesis
- Assumed some features of canine apply
- PF is most common form of auto-immune skin condition in the cat
- Drug eruption documented as underlying case, incl. antibiotics
Describe the pathogenesis of pemphigus vulgaris
- Autoimmune blistering skin disease
- Generation of autoantibodies that target transmembrane desmosomal proteins in the epithlium
- Desmoglein 3 at the bottom of the epidermis affected, leading to lifting of the entire epidermis
Describe canine discoid lupus erythematosus (DLE) (appearance, prevalence, disease process, cause)
- Long nosed dogs
- Leads to crusty nosed appearnce, erythematous
- May be as common as pemphigus foliaceous
- Photosensitive dermatosis that involves the nasal planum
- Can be related to stress
Outline the pathogenesis of plasma cell pododermatitis
- Immune mediated? Aetiology unknown
- Leads to lymphocytosis of affected tissues and positive ANA titres
Give an example of a primary vasculitis in animals
Multisystemic necrotising vasculitis of small vessels in beagles = Juvenile Polyarteritis syndrome (JPS)
Compare the prevalence of primary and secondary cutaneous vasculopathies
Usually secondary to an underlying process
List potential causes of secondary vasculities in veterinary medicine
- Infection
- Vaccination
- Drugs:
- Allergy
- Immune mediated
- Other
- Idiopathic
- Sepsis and vascular toxins
Give examples of infections that may cause vasculitis
- Bacterial (incl. endocarditis via Staphylococus intermedius)
- Mycobacterial
- Funga
- Viral (FIP, FeLV, FIV, parvo)
- Protozoa (e.g. Leishmaniasis0
- Rickettshial (RMSF, Ehrlichia, Borrelia)
- Sarcocystis
Give examples of vaccinations that may cause vasculitis
- Rabies
- Hyposensitisation
- Sera
Give examples of drugs that may cause vasculitis
- Antibiotics
- Ivermectin
- Vaccines
- Metronidazole
- Phenobarbitol
- Frusemide
- Itraconazole
- Phenylbutazone
- Enalapril
- Imodium
- Metoclopramide
- Fenbendazole