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Y4 SA - Dermatology > Immune mediated skin disease > Flashcards

Immune mediated skin disease Flashcards

1
Q

What is an immune mediated skin disease?

A

The immune system fails to tolerate self antigens and it mounts a response against normal skin components

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2
Q

What is a primary immune mediated skin disease?

A

No identifiable trigger factor present = idiopathic

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3
Q

What is a secondary immune mediated skin disease?

A

Exogenous trigger antigen, most commonly drug, bacteria or virus

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4
Q

How you should patients with potential immune mediated skin disease be clinically assessed?

A
  • Consider signalment (particularly breed) & key historical features
  • Look for primary lesions
  • Look at distribution of lesions
  • Make differential diagnosis list
  • Run tests according to differentials
  • Interpret results in line with clinical findings
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5
Q

List some diagnostic tests that can be used to diagnose immune mediated skin disease

A
  • Skin scrapes & trichography
  • Lesion cytology
  • Bacterial/fungal culture and susceptibility testing
  • Haematology, biochemistry: to give a general picture of the animal’s heath before treatment
  • Urinalysis
  • Diagnostic imaging: radiography, ultrasonography
  • Blood smear cytology
  • Coombs test
  • Antinuclear antibody (ANA) test
  • Skin biopsy & histopathology
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6
Q

How is cytology used to narrow down the DDX

A

Cytology to differentiate sterile from infectious disease (and rule out secondary bacterial infection)

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7
Q

How is skin biopsy and histopathy used to narrow down the DDX

A

Rule out neoplasia, atypical infectious diseases and determine skin pathology (definitive diagnosis)

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8
Q

What are the advantages of cytology

A

Easy, cheap, rapid (in house) results
Differentiate sterile from septic (infectious) disease
Determine type of inflammation
May inform management prior to histopath results

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9
Q

Mixed neutrophils and macrophages indicate what type of inflammation?

A

Sterile pyogranulomatous inflammation

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10
Q

Neutrophils with cocci bacteria indicate what type of inflammation?

A

Coccoid bacterial inflammation

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11
Q

Direct impression smears can be used for which lesion types?

A

Pustules, exudative lesions (erosions, ulcers), draining tracts

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12
Q

FNA can be used for what types of lesions?

A

Nodules, plaques, tumours, lymph nodes

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13
Q

When in the diagnostic process in skin biopsy and histopathology used?

A

Test often comes after cytology once the differential list has been narrowed down

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14
Q

Where are samples taken when doing skin biopsies?

A
  • Take multiple biopsies +3
  • Sample primary lesions
  • Sample range of lesions to represent disease process
  • Sample whole lesion where possible
  • Avoid eroded / ulcerated lesions (or sample from margin to include epidermis) - If only these lesions are present you need to sample from the lesion margins
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15
Q

Name the 4 most common primary lesions seen in immune mediated skin disease

A
  • Pustules
  • Plaques/nodules
  • Erythematous macules/patches
  • Hypopigmented macules/patches
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16
Q

List some other lesions seen in immune mediated skin disease

A

Alopecia
Vesicles
Erosions/ulcers
Crusts
Purpura
Scale

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17
Q

Define an erosion

A

Loss of the surface layer of the epidermis

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18
Q

Define an ulcer

A

Loss of full thickness of the epidermis

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19
Q

Are ulcers and erosions primary or secondary lesions?

A

Secondary
- less helpful in making DDx

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20
Q

What are the most common causes of ulcers and erosions?

A

Keratinocyte death, loss of KC adhesion, self trauma (pruritus), secondary bacterial infections

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21
Q

What are crusts?

A

Dried exudate on skin surface
- Pus from pustules
- Exudate from erosions/ulcers
- Blood

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22
Q

Define a pustule

A

A circumscribed elevation of skin containing pus
Pus is formed from infiltrating neutrophils

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23
Q

Case 1:
- Physical examination = General WNL except pyrexia 40oC and mild peripheral lymphadenomegaly
- Lesion morphology = Rare pustule, thick, adherent crusts, pus, erosions
- Lesion distribution = Multifocal - Dorsal muzzle, periocular, medial pinnae, footpads

What are the 4 DDx?

A
  • Bacterial infection (pyoderma/folliculitis)
  • Pemphigus foliaceus
  • Superficial pustular drug reaction (rare)
  • Superficial pustular dermatophytosis (rare)
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24
Q

What are acantholytic keratinocytes?

A

Large epithelial cells (larger than neutrophils) – rounded (normal keratinocytes are normally anuclear and angular)

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25
Q

Describe the pathophysiology of canine pemphigus foliaceous

A
  • Auto-antibodies (mainly IgG) target components of desmosomes that link keratinocytes in superficial epidermis
  • Separation of KCs > acantholytic ‘rounded up’ KCs
  • Neutrophilic inflammatory response > superficial pustules with free floating acantholytic KCs
26
Q

Describe the appearance of pemphigus foliaceous on histopathology

A

Subcorneal (superficial) pustular dermatitis with acantholytic keratinocytes

27
Q

Name the most common autoimmune skin disease of dogs

A

Pemphigus foliaceus

28
Q

Describe the signalment of pemphigus foliaceus

A

Middle aged (any), predisposed breeds akita, chow chow, cocker spaniel, dachshund, Labrador retriever, British bulldog & Shetland sheep dog (affects many breeds)

29
Q

Describe feline pemphigus foliaceous

A
  • Less common than dog PF
  • Signalment: X
  • Lesion distribution: face, claw fold (paronychia) and nipples
  • Prognosis fair
30
Q

Define a plaque

A

Flat elevation of skin more than 1cm in diameter. Cause by infiltration of cells of coalition of papules

31
Q

Define a nodule

A

Circumscribed solid elevation > 1cm diameter, usually extending into deeper skin layers. Caused by massive infiltration of cells

32
Q

Describe the signalment of Eosinophilic furunculosis of the face

A

Young adults

33
Q

How does Eosinophilic furunculosis of the face present?

A

History: rapid onset, intense pruritus
Lesion morphology: eroded/ulcerated plaques and nodules
Distribution: face
Cytology: eosinophilic inflammation
Histopathology: eosinophilic folliculitis & furunculosis

34
Q

Describe the signalment of Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis)

A

Puppies (sporadic cases in adults)

35
Q

How does Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis) present?

A

History: acute onset, non-pruritic (painful), pyrexia, lethargy
Lesion morphology: follicular nodules (furuncules) & plaques (often eroded & crusted), diffuse swelling, alopecia (check for Demodex), lymphadenomegaly
Distribution: face (muzzle, periocular, pinnae), lymph nodes

36
Q

Describe the cytology and histology of Sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis)

A

FNA cytology: sterile pyogranulomatous inflammation
Histopath: sterile perifollicular granulomatous-pyogranulomatous inflammation & furunculosis

37
Q

Define a macule

A

flat area of skin discolouration < 1cm diameter

38
Q

Define a patch

A

flat area of discolouration > 1cm diameter

39
Q

List 3 DDx of Hypopigmented or erythematous macules & patches

A

Hypopigmentation, erythematous macules/patches, erosions/ulcers

40
Q

Describe the clinical presentation of facial discoid lupus erythematous

A
  • Loss of cobblestone surface
  • Hypopigmented macules and patches
  • Erosions, ulcers and crusting
  • Black to blue to pink pigmentary change
  • Note biopsies taken from blue pigmentary change rather than ulcers or crusting
  • Hypopigmentation, erosion, crusting periocular skin and lips
  • Severe ulceration and crusting
41
Q

Describe the history of an animal with Erythema multiforme (major/minor)

A

Acute onset, non-pruritic, +/- systemic signs (pyrexia, lethargy, inappetence)
Trigger: virus, drug, vaccine, microbial infection, neoplasia, systemic disease, food (can be idiopathic)

42
Q

Describe the lesions seen in cases of Erythema multiforme (major/minor)

A
  • Primary lesion = annular erythematous macule (may be targetoid)
  • Can see vesicles, bullae, wheals, ulceration, crusts
  • Distribution: ventral abdomen > generalised, mucosae (often oral cavity)
43
Q

Describe the ‘target lesions’ seen in erythema multiforme major/minor

A

Erythematous macules spread peripherally producing annular or arciform pattern
- Central erythema/pupura, ring of clear oedema (may be raised), ring of erythema = target lesion
- Centre may be a vesicle/bulla resulting in ulcers and crusts

44
Q

Describe the cytology and histopathology of erythema multiforme major/minor

A

Cytology: sterile non-specific inflammation (NB ulcers may be secondarily infected!)
Histopathology: keratinocyte apoptosis (death), lymphocyte satellitosis, interface (epidermis/dermis) dermatitis

45
Q

The degree of apoptosis in erythema multiforme determines?

A

Severity of epithelial loss i.e. EM vs SJS vs TEN

46
Q

Describe the main features of hyperkeratotic erythema multiforme

A

Chronic, persistent
Older dogs
Idiopathic
Lesions more exudative and crusting
Often face and ears but can be generalised

47
Q

Describe Stevens-Johnson syndrome

A

Erythema multiforme
No target lesions
More ulcerative – lose large sections of skin
Guarded prognosis

48
Q

What is the signalment of Uveodermatologic syndrome

A

young to middle aged, Akita predisposed

49
Q

Describe the history and clinical presentation of Uveodermatologic syndrome

A

History: acute bilateral uveitis, non-pruritic
Lesion morphology: hypopigmented macules > patches, erythematous macules, erosions, ulcers, crusts
Distribution: face; nose, lips, periocular skin (occasionally footpads, scrotum, perineum)

50
Q

List the DDx for immune mediated alopecia

A

Sebaceous adenitis
Alopecia areata
Dermatomyositis
Ischaemic dermatopathy
Post-injection alopecias

51
Q

Which test is used to rule out demodicosis and dermatophytosis?

A

Trichography +/- skin scrapes

52
Q

Describe the signalment of sebaceous adenitis

A

Standard poodle, Akita, vizsla, *autosomal recessive mode of inheritance

53
Q

How does sebaceous adenitis present?

A

History: non-pruritic unless SBI
Lesion morphology: partial alopecia and poor coat quality, follicular casts and scale
Distribution: generalised

54
Q

Describe the cytology and histopathology of sebaceous adenitis

A

Cytology: no significant findings unless SBI
Histopath: pyogranulomatous inflammation targeting sebaceous glands > destruction of sebaceous glands and hair follicle atrophy

55
Q

Describe how cases of alopecia areata present

A

History: non pruritic, chronic onset
Lesion morphology: focal to multifocal, partial to complete patches of alopecia +/- erythema and hyperpigmentation
Distribution: head/face

56
Q

Describe the histological appearance of alopecia areata

A

Lymphocytic destruction of hair bulbs

57
Q

Describe the signalment of Dermatomyositis/ischaemic dermatopathy

A

Young collies, SSD, Beauceron shepherd, Belgian shepherd, PWD predisposed to dermatomyositis (familial)

58
Q

Describe the clinical presentation of Dermatomyositis/ischaemic dermatopathy

A

History: non-pruritic, chronic course +/- myositis
Quite a rare disease
Lesion morphology: focal to multifocal alopecia with variable hyperpigmentation, hypopigmentation, scaling, erosion/ulceration & crusting
Distribution: face and extremities (dorsal digits, pinnae & tail tips, nails)

59
Q

Describe the histological appearance of Dermatomyositis/ischaemic dermatopathy

A

Chronic dermal & vascular inflammation > follicular atrophy (include muscle in biopsy to check myositis)

60
Q

How is immune mediated disease managed?

A
  • Removal/treatment of any external triggers e.g. Drugs, UV light: sunscreen, food
  • Control of inappropriate immune response: Immunosuppressive/immunomodulatory drugs

Y4 SA - Dermatology (6 decks)

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