Autoimmune and Immune mediated skin diseases 2 Flashcards
Autoimmune, immune mediated, allergy, management of allergic skin disease
Explain the use of tetracyclines in the treatment of CLE/DLE (modes of action)
- Inhibits neutrophil and leukocyte chemotaxis
- Inhibits degranulation and phagocytosis
- Inhibits lymphoblast formation/proliferation/antibody production
- Inhibits activation of complement C3
- Increases prostaglandin synthesis
- Inhibits lipases and collagenases
What are the treatment options for plasma cell pododermatitis?
- Resolution without therapy
- Glucocorticoids
- Gold salts
- Chlorambucil
- Surgery
- Doxycycline
- Ciclosporin, but not documented
How are glucocorticoids used in the treatment of plasma cell pododermatitis?
Prednisolone 4mg/kg/day initially, subject to change
How long until gold salts show an effect in the treatment of plasma cell pododermatitis
Can take up to 12 weeks to full effect
Outline the use of chlorambucil in the treatment of plasma cell pododermatitis
In combination with other drugs, especially steroids
Discuss the role of surgery in the treatment of plasma cell pododermatitis
- Effective in severe cases, esp. where bleeding may be a major problem
- Pad tissue regrows after the srugery
Discuss the use of doxycycline in the treatment of plasma cell pododermatitis (dose, long term use, mode of action)
- 5mg/kg BID for up to 3 weeks
- May have initial improvement allowing pulse therapy or low dose continuous therapy
- Mode of action presumed immune mediate effects
Outline the management of idiopathic symmetric lupoid onychodystrophy when the nails start to lift off
- Sedate/anaesthetise
- Remove all loose nails
- Bandage and antibacterial therapy combined with NSAIDs for pain relief
Describe the long term treatment of ILSO
- Will have recurrent bouts of nail loss
- Pentoxifylline (Trental), or tetracycline and niacinamide
- Severe cases: glucocorticoids, ciclosporin
- Keep nails short to avoid catching and ripping (main management)
Outline the treatment of vasculitis
- Remove underlying cause
- Outcome dependent on organs affected
- Glucocorticoids are mainstay of treatment using immunosuppressive doses
- Alternate therapies: pentoxifylline, sulphasalazine, dapsone
- Sulphasalazine and dapsone not commonly used
What is pentoxifylline?
Methylxanthine derivative and phosphodiesterase inhibitor
What is the key risk owners need to be aware of when usinng pentoxifylline?
Risk of kidney failure
What are the effects of pentoxifylline?
- Immunomodulatory (inhibits pro-inflammatory cytokines, upregulates anti-inflammatory IL-10)
- Stimulates wound healing by stimulating collagenase production
- interferes with adhesion of inflamm. cells to endothelial cells and keratinocytes
- Decreases blood viscosity by inhibition of platelet aggregation
What conditions is pentoxifylline used for?
- Vasculitis
- Contact allergic dermatitis
- Erythema multiforme
- Dermatomyositis
- Ulcerative dermatitis syndrome of rough collies
What are the 3 main groups of conditions that will cause pruritus?
- Infections
- Allergic skin disease
- Ectoparasites
List potential differentials for pruritus/allergic skin disease
- Ectoparasites hypersensitivities
- Environmental atopy
- Cutaneous adverse food reactions (CAFR) (dietary allergens and intolerance)
- Contact allergy
- Drug reactions
Define atopy
Inherited predisposition to develop a type I hypersensitivity reaction to environmental allergens
What is atopy-like dermatitis/intrinsic atopy?
Atopy with no IgE demonstrable (atopy usually associated with IgE)
What 2 defects are required in order for canine atopic dermatitis to develop?
- Epidermal barrier function defect, allowing entry of percutaneous allergens from the environment
- Polarisation of lymphocytes towards Th2, instead of Th1, routes
What steps are involved in the pathogenesis of canine atopic dermatitis?
- Sensitisation and epidermal barrier defect
- Re-exposure to the allergen
- Direct neuronal stimulation
- Chronicity
Explain the sensitisation and epidermal barrier defect step in the pathogenesis of canine atopic dermatitis
- Percutaneous exposure to allergen leads to allergen capture and processing by Langerhans cells -> presented to naiive T lymphocytes, production of Th2 lymphocytes
- Production of IL-4, IL-5, IL-13, activate skin immune system, stim, class switchin gin B cells = prod. of allergen specific IgE
- Tissue mast cells bind IgE, sensitised to allergen
- Additional IgE on basophils, langerhans cells and in circulation
- Period of sensitisation before allergy
What is expressed by mast cells that allows binding to the allergen specific IgE in canine atopic dermatitis?
High-affinity Fc Epsilon receptors
Describe the re-exposure to allergen step in the pathogenesis of canine atopic dermatitis
- Cross linking of mast cell surface IgE by allergen -> degran. of MCs -> released of preformed mediators and new synthesis -> cytokines from keratinocytes, activated T cells
- Recruitment of inflamm. cells to dermis
- Inflamm cells activate and proliferate via Janus Kinase (JAK) pathways on cell surface
- Leads to inflammation, itch and scratch, worsen epidermal barrier, epidermal hyperplasia, worsening of epidermal barrier function
Explain the direct neuronal stimulation step in the pathogenesis of canine atopic dermatitis
- On re-exposure, LC recognises allergen, migrates to dermis, presents allergen to primed Th2 cells
- Pro-inflamm cytokines e.g. IL-31 released, bind to receptors on surface of neurons, trigger activation of JAK enzymes, stimulate nerve
- Leads to itch then scratch
Explain the role of chronicity in the pathogenesis of canine atopic dermatitis
- Scratching, toxins from secondary microbial infections, continued exposure to allergens all lead to progression of atopy
- Activate keratinocytes and other immune cells e.g. macrophages
- IL-12 released
- Polarisation to ?Th1 phenotype => release of IFN-y increases monocyte/macrophage recruitment and activation
- Leads to thickening of epidermis, stratum corneum etc.
- Further worsening of epidermal barrier function
What are the 3 phases of inflammation seen in canine atopic dermatitis?
- Acute phase
- Late phase
- Chronic phase
Describe the acute phase of inflammation in canine atopic dermatitis
- Th2 cytokine profile
- 15-20 mins after initiation
- Inflammatory mediators released from mast cells (e.g. histamine, serotonin, PGs)
- Effect is local vasodilation, tissue oedema, influc of inflammatory cells
- Often pruritus
Describe the late phase of inflammation in canine atopic dermatitis
Eosinophil dominated, seen after 6-12 hours
Describe the chronic phase of inflammation in canine atopic dermatitis
- Subsequent infiltration of lymphocytes
- Th1 dominated or unpolarised cytokine profile
Compare feline and canine atopic dermatitis
- Poorly defined in cats
- Not simple Th2 bias in lesional skin in cats
- Cats referred to as “non-flea, non-food induced hypersensitivity dermatitis” i.e. hypersensitivity proven to not be food or fleas and therefore assume environmental
Describe the typical presentation for feline atopic dermatitis
- Chronic, relapsing disease
- May be seasonal or perennial
- Hypersensitivity proven to not be food or fleas
- May present at young age (6mo-3yr)
- Genetic predilection recognised by some reports, esp. purebreds
What is allergic respiratory and cutaneous disease recognised for in horses?
Culicoides/insect bite hypersensitivity and atopic dermatitis
Give examples of allergens implicated in equine atopic dermatitis
- Dust mites, forage mites (>90%)
- Dust extracts, epidermals, feathers
- Mould spores
- Tree, grassweed pollens
- Concurrent insect-bite hypersensitivity
What is meant by cutaneous adverse food reaction?
Inappropriate reactions to elements of diet
Compare food intolerance and dietary hypersensitivity
- Intolerance: non-immunological mechansism
- Hypersensitivity: immunological mechanisms, not just type I hypersensitivity
What are the potential manifestations of CAFR?
- GI disease
- GI + cutaneous disease
- Cutaneous disease alone
Compare the prevalence of atopic dermatitis and CAFR in dogs and cats
- CAFR uncommon in dogs, whereas AD is common
- CAFR may be as common as AD in cats
Compare the clinical appearance of atopic dermatitis and CAFR
Are clinically indistinguishable
Outline the development of CAFR
- Require sensitisation, generally over long period of time
- Must be exposed to diet before
- Clinical signs generally when diet has been eaten long term
- Allergens poorly characterised and geographical differences likely
- May react more to one protein
Describe the onset of clinical signs of CAFR
- Can be within minutes of exposure
- More often 4-24 hours after ingestion