Derm 9 - more allergies Flashcards
How to identify an allergic cat - Hypersensitivity Reaction Patterns
> what are they?
> common patterns?
- cats “like” to do the same thing differently! Feline cutaneous hypersensitivity reaction patterns are various presentations that cats have when they are exhibiting a hypersensitivity reaction.
- Head and neck pruritus,
- miliary dermatitis,
- eosinophilic granuloma complex (eosinophilic granuloma, eosinophilic ulcer, eosinophilic plaque)
- and feline self trauma
> are all variations of the same theme
Head and neck pruritus - when to we see it in cats? Ddx?
- “Head and neck pruritus” is a common hypersensitivity presentation of a patient with an adverse food reaction.
- However, other differentials will include herpes viral dermatitis
Miliary dermatitis in cats - what does it look like, what should we consider?
- If a patient presents with miliary dermatitis, a crusted papular eruption, one should consider flea allergies as it is one of the most common underlying causes.
- However, there are many other causes that should be considered including food allergies, atopic dermatitis and even dermatophytosis.
Eosinophilic granuloma complex - what is this?
- what is included? what do they look like?
a group of hypersensitivity reaction patterns that can present as eosinophilic granulomas, indolent ulcers or eosinophilic plaques
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Eosinophilic granuloma can present in a number of ways, eg:
- “pouty lip”
- linear plaque on the caudal aspect of the hind legs
- plaque-like lesions on the soft palate and tumours under the tongue
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Indolent ulcers (also known as eosinophilic ulcers or rodent ulcers)
- often on lips, Ddx SCC
- may respond to antibiotic therapy
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Eosinophilic plaques
- erythematous, oozing, raised lesions that typically are found on the inner thigh or ventral abdomen
- secondary infection common
- may respond to antibiotic therapy
is feline self-trauma generally a behavioural issue? relationship to allergies, other conditions?
In one study:
- 76% had a purely medical etiology
- 57% of the cases in that study adverse food reactions played a role
- 52% were multifactorial
- In 14.3% of the cases, psychogenic alopecia played a role
- Only 9.5% of the cases were purely behavioural in origin.
how to differrentiate flea from non-flea hypersensitivity disease
- Widespread lesions are less supportive of food or fleas
- multiple reaction patterns make fleas less likely to be the sole cause
- miliary dermatitis in dorsal distribution more likely flea allergy , but less likely flea related when not in dorsal distribution
Criteria set for the diagnosis of feline NFHD ((NFHD = Non-Flea Hypersensitivity Dermatitides)
- Presence of at least two body sites affected
- Presence of at least two of the four following clinical patterns:
a) Symmetrical alopecia
b) Miliary dermatitis
c) Eosinophilic dermatitis
d) Head and neck erosions ⁄ ulcerations - Presence of symmetrical alopecia
- Presence of any lesion on the lips
- Presence of erosions or ulcerations on the chin or neck
- Absence of lesions on the rump
- Absence of nonsymmetrical alopecia on the rump or tail
- Absence of nodules or tumours
is feline self trauma all about allergies? how many cases have non-allergic etiology?
In one study (Hobi et al) 24% had a non-
allergic etiology
> Numerous conditions (parasitic, viral, fungal, autoimmune and neoplastic) must be ruled out before a diagnosis of hypersensitivity disease can be confirmed
non-allergic medical causes of feline self trauma
- ectoparasites
- infectious (dermatophytosis, Malassezia, Herpes
viral dermatitis, bacterial (rare)) - Localized: neuropathic pain / idiopathic ulcerative dermatitis
- utricaria pigmentosa (cutaneous mastocytosis)
- Cutaneous T-cell lymphoma -
Mycosis fungoides (exfoliative erythroderma)
viral disease of cat often misdiagnosed as allergy? why?
- Herpes viral dermatitis can easily be misdiagnosed as allergic skin disease
- It presents as crusted skin lesions, often at the nose and periocular skin. When the crusts are removed, the exposed skin is inflamed and ulcerated
- On histopathology, the dermis is intensely and diffusely inflamed, usually with eosinophils predominating
(environmental) atopic dermatitis pathogenesis
- Epidermal barrier defects play a significant role but it is unclear in dogs whether there is a primary defect or the defect is secondary to the release of various mediators of inflammation.
> Regardless, these defects are thought to facilitate percutaneous absorption of environmental allergens - The allergens are processed by antigen presenting cells
- These cells then travel into lymph nodes where they trigger the activation of T-cells and the release of
cytokines such as IL-4 and IL-13 and subsequent production of allergen specific IgE - The activated T cells migrate back to the skin
- Following sensitization, when Langerhans cells with allergen specific IgE are exposed to the same allergen it can rapidly trigger the activation of T-cells, which in turn release pruritogenic cytokines
- One of these cytokines, IL-31, has recently become the focus of much research and discussion in the veterinary dermatology community
how are environmental allergies diagnosed?
Diagnosis of exclusion
Control for parasites, infection, food….
what does a positive allergy test mean? can we make a diagnosis?
A positive allergy test, whether performed as an in vivo test or in-vitro test, means that the test was positive; it does NOT mean that allergies are the cause of the itchiness. These tests should never be performed to make a diagnosis
Intradermal skin testing - use
- Intradermal skin tests (IDT) are still considered by most dermatologists to be the gold standard in
veterinary medicine as it tests the target organ. - However, there are cases where in vitro allergy
testing (IVAT) is indicated. - injections of allergens in grid pattern
in vitro allergy testing methodology
- serum is allowed to interact with allergen extract
- unbound antibodies are washed away
- allergen bound IgE is detected using a reagent specific for IgE
- Amount of IgE is quantified
