Immune mediated skin disease Flashcards
What are immune mediated skin disease?
- Immune system fails to tolerate self-antigens
- Mounts response against normal skin component
What’s the difference between primary + secondary IMSD
- Primary IMSD = No external trigger identified (idiopathic)
- Secondary IMSD = Exogenous triggering antigen, most commonly drug, bacteria or virus
What clinical assessment should be done with IMSD?
- Consider signalment (particularly breed) & key historical features
- ID primary lesions
- Consider lesion distribution
- Make differential diagnosis list
- Run tests according to differentials
- Interpret results in line with clinical findings
What are IMSD lesions?
- Pustules - common
- Plaques/nodules - common
- Erythematous macules/patches - common
- Hypopigmented macules/patches - common
- Alopecia
- Vesicles
- Erosions/ulcers - secondary - loss of blood supply, adhesion, self trauma
- Crusts - secondary - pus. exudate, blood (dried)
- Purpura (haemorrhage/bruise)
- Scale
How can you diagnose IMSD?
- Lesion cytology
- Skin biopsy & histopathology
- Haematology, biochemistry, urinalysis
- Diagnostic imaging = radiography, ultrasonography
What are advantages of cytology?
- Easy, cheap, rapid (in house) results - direct impression / FNA
- Differentiate sterile from septic (infectious) disease
- Determine type of inflammation
- May inform management prior to histopath results
What are benefits of skin biopsy + histopath?
- Definitive diagnosis - rule out differentials, determine skin pathology
Case 1 =
Betty = 7yr FN springer spaniel
* Hx = 10wk non-pruritic progressive crusting dermatosis
- reduced appetite last 3 days
* Physical examination =
- General WNL except pyrexia 40oC and
- mild peripheral lymphadenomegaly
* Lesion morphology =
- Thick, yellow adherent crusts, pus under crusts
* Lesion distribution =
- Multifocal
- Dorsal muzzle, periocular, medial pinnae, footpads
What are differentials for pustules?
- Bacterial infection (pyoderma/folliculitis)
- Pemphigus foliaceus
- Superficial pustular drug reaction (rare) - ruled out as not had drugs
- Superficial pustular dermatophytosis (rare)
Betty’s cytology =
- Direct impression smear =
- Needle rupture of intact pustule or
- Below crust after gentle removal
- Microscopy =
- Sterile neutrophilic inflammation and acantholytic keratinocytes +/- eosinophils
- what does this indicate from the differentials?
= Consistent with pemphigus foliaceus
How do acantholytic keratinocytes form with pemphigus foliaceus?
- 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
What are signalment + history indications of pemphigus foliaceus?
- Signalment =
- middle aged (any), predisposed breeds = akita, chow chow, cocker spaniel, dachshund, LR, BBD & SSD (affects many breeds)
- History = variable pruritus, possible drug-trigger (including topical and oral ectoparaciticides)
- Often UV exacerbation
Case 2
Bernie
* Signalment = 6 yr FN Basset hound
* History = 4 yr CAD & Malassezia dermatitis
- ASIT, itraconazole (5-10mg/kg), topical chlorhexidine & miconazole
- Acute onset non-pruritic lumps and discharging tracts
* Physical examination = General WNL
* Lesion morphology =
- 3-8 cm (huge) soft nodules (fixed to dermis)
- Overlying skin normal or erythematous and ulcerated, draining serosanguinous fatty fluid
* Lesion distribution = Trunk and proximal limbs
- What are differentials for plaques + nodules?
- Immune mediated =
- Juvenile sterile granulomatous dermatitis and lymphadenitis (juvenile cellulitis)
- Sterile pyogranulomatous dermatitis and panniculitis
- Feline plasma cell pododermatitis (not a cat)
- Canine eosinophilic furunculosis of the face
- Reactive histiocytosis
- Canine eosinophilic granuloma
- Metatarsal fistulation (of GSD)
- Canine sterile neutrophilic dermatosis (Sweet’s syndrome)
- Canine acute eosinophilic dermatitis
- Cutaneous xanthoma
- Other =
- Neoplasia
- Callus
- Acral lick dermatitis
- Deep infections: mycobacterial, fungal, protozoal
- Arthropod/spider bites
- Foreign body reaction
- Feline eosinophilic plaque or granuloma - not a cat
- Calcinosis cutis/circumscripta
- Sterile pyogranulomatous
- pododermatitis (interdigital furunculosis/interdigital cysts)
What is seen with eosinophilic furunculosis of the face?
- Signalment = young adults
- History = rapid onset, intense pruritus
- Lesion morphology = eroded/ulcerated plaques and nodules
- Distribution = face
- Cytology = eosinophilic inflammation
- Histopathology = eosinophilic folliculitis & furunculosis
What is seen with sterile granulomatous dermatitis + lymphadenitis (juvenile cellulitis)?
- Signalment = puppies (sporadic cases in adults)
- 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
- FNA cytology = sterile pyogranulomatous inflammation
- Histopath = sterile perifollicular granulomatous- pyogranulomatous inflammation & furunculosis
What can be done to rule out Ddx?
- FNA cytology - deep infections - mycobacterial, fungal, protozoal
- Skin biopsy + histopath (take extra biopsy + freeze)
