Pustules Flashcards
what is a pustule?
elevated, circumscribed, full of granulocytes (degenerate or normal)
-different from vesicles and bullae, which are fluid filled but NOT full of pus
describe superficial pyodermas
- extremely common in dogs, rare in cats, seen in horses
- canine:
-S. pseudintermedius: most common causative agent
-S. schleferi: isolated in some cases
-primary/idiopathic: no research, dx by exclusion
-secondary pyoderma: MOST COMMON FORM, almost always due to an underlying disease!! - horses:
-MRSA - assume some zoonotic risk
- staph infections usually secondary to an underlying cause:
-skin barrier defect
-dermatitis
-ectoparasites
-immunologic, endocrinologic, or metabolic disorder
what are the 3 most common underlying causes of secondary canine pyoderma?
- atopic dermatitis (food and/or environment induced)
- endocrinologic disease: Cushing’s, hypothyroid
- tumors
describe staphylococcal folliculitis
- common in dogs and horses
-folliculitis = affects infundibulum/upper part of hair follicle - lesions:
-erythematous papules that progress to pustules and eventually crusts
-pustules generally small, centered on hair follicles, and isolated
-typically do not coalesce
-areas: abdomen, groin, medial thighs, axillae
-pruritis frequent - bacterial pastern folliculitis:
-staph or D. congolensis
-lesions limited to posterior pastern and fetlock, papules and pustules
describe staphylococcal impetigo
- not very common
-impetigo = affects interfollicular epidermis (sometimes expands in large areas and engulfs hair follicles) - due to exfoliative toxins that cleave desmoglesin in desmosomes and produce superficial epidermal blisters
- lesions:
-large pustules that rupture easily, leaving large crusts
-usually isolated and enlarge slowly
-no coalesce - S. pseudintermedius is main causative agent; produces exfoliative toxins EXPA and EXPB that cleave desmosomes and produce acantholytic keratinocytes
describe staphylococcal epidermal collarettes
- common in dogs and seen in horses
- lesions:
-rapidly expanding erythematous rings with peripheral peeling/crusting
-center can be hyperpigmented or normal appearing, NO bacteria in center
-leading edge contains inflammation with neutrophils and bacteria under the crusting
-can sometimes coalesce to cover large areas with polycyclic pattern - S. pseudintermedius most common agent
describe diagnostic procedures for superficial pyoderma
- cytology (aspiration, smear, swab): KEY
-neutrophils as well as extracellular and intracellular cocci within neutrophils - bacterial culture and sensitivity
- response to antibacterial therapy
- skin biopsy (rare)
describe treatment of superficial pyodermas
FIRST: ID and address underlying disease
- ALWAYS topical antimicrobials!
-systemic reserved for those that fail topical therapy due to developing resistance
-clip lesions and remove crusts prior to application!! MOST IMPORTANT STEP OF TX PYODERMA
-2-3x weekly antiseptic shampoos (chlorhexidine based, min contact time of 10-15 min, more contact time = better)
-once to twice daily topical antimicrobials (sprays, ointments, gels) - antiseptic agents:
-chlorhexidine!! best evidence base
-benzoyl peroxides: can be drying or irritating
-silver sulfadiazine
-ethyl lactate
-triclosan - antibiotic agents:
-mupirocin
-erythromycin
-clindamycin
-gentamycin
list the antibiotics used orally/systemically in dogs for superficial pyoderma
continue for at least 3 weeks or 1 week beyond clinical remission, whichever is longer!
-if need treatment to be faster (like has surgery in a week)
-first line (cephalosporins, clindamycin)
- beta lactams:
-cephalexin
-amoxicillin clavulanate
-cefpodoxime - macrolides: clindamycin
- fluoroquinolones:
-enrofloxacin
-marbofloxacin - sulfonamides: trimethoprim sulfa
describe treatment of PRIMARY/IDIOPATHIC pyoderma in dogs
- antibacterial topical agents (twice weekly shampoos)
- bacterial vaccines:
-staphage lysate: S. aureus extract
-immunoregulin: prioprionibacterium acnes extract
list the antibiotics used systemically in horses for treatment of superficial pyoderma
treat for 1 week beyond clinical remission!!
-like dogs, topical treatment and clipping hair is key!! before get to systemics
- sulfonamides: TMS, most common
- beta lactams:
-IM penicillin
-IV or IM ceftiofur sodium
describe pustular dermatophytosis
VERY RARE
- due to trichophyton spp. with proteases that cleave desmosomes
- identical treatment as for any dermatophytosis
Interpret the cytological examination of pustular contents and be able to
distinguish superficial pyoderma from pemphigus foliaceus
- bacterial folliculitis: degenerated neutrophils with intracellular bacteria
- bacterial impetigo: same for bacterial folliculitis with free floating (acantholytic) epidermal cells (separated after bacterial toxin action)
- epidermal collarettes:
-from leading edge: same as bacterial folliculitis with sometimes free floating acantholytic epidermal cells like for impetigo - pemphigus foliaceus:
-bacteria ABSENT
-neutrophils INTACT, not vacuolated
-+/- eosinophils
-some epidermal cells are free floating
-looks like a vaginal smear of a bitch in diestrus (neutrophils with epithelial cells)
-need INTACT PUSTULE for histo!!
what is the most common canine pustular disease? describe the sequence of clinical lesions that occur in patients
pemphigus foliaceus
pathogenesis:
1. autoantibodies specific for desmosomal proteins disrupt keratinocyte adhesion and result in cell-cell separation (acantholysis)
- neutrophils are attracted to the region and end result is a pustule with acantholytic keratinocytes
-main dog antigen is desmocolin-1; akitas and chows predisposed
Describe the classical clinical presentation of pemphigus foliaceus across animals
lesions:
1. progress from small to large, irregular and coalescing pustules to erosions and crusts, sometimes with alopecia
-pustules = early in dz, easy to diagnose
-erosions and crust = harder to differentiate from pyoderma
- severity waxes and wanes but rarely spontaneous remission
- lesions distribution:
-2 main phenotypes:
–classic form: bilaterally symmetrical on nasal bridge, nasal planum, periocular, inner ear pinnae, footpads
–generalized form: thorax +/- facial/footpads
-cats: affects claw skin folds: severe crusting with accumulation of purulent to caseous exudate with erosion to ulcerations (erosions and crusting more dominant in cats)
-other lesions distribution similar to dogs
-equine: transient pustules quickly dry to create layers of crusts (crusting exfoliative dermatitis common)
describe diagnosis of pemphigus foliaceus
- rule out superficial pyoderma, demonstrate compatible cytology
-cytology: ideally collect samples of pustules and underneath crusts; neutrophils, acantholytic keratinocytes, no bacteria!!
-rule out other diseases with acantholytic keratinocytes: superficial pyoderma and staphylococci withe exfoliative toxins, pustular dermatophytosis
- if doubt: bacterial culture of intact pustular material is usually sterile
- skin biopsies for histopathology:
-need INTACT PUSTULE
-superficial epidermal pustules with acantholytic keratinocytes
-negative special stains to rule out bacteria/dermatophytes
-do NOT scrub skin!! (will remove material)
Understand the therapeutic management of pemphigus foliaceus across animals,
including the side effects and recommended monitoring for the medication- associated side effects
eliminate any possible causative factors (UV light, drug triggers (ectoparasitic treatments = why we start on dorsum when start treatment))
dogs:
1. begin with glucocorticoids + additional steroid-sparing immunosuppressants
-azathioprine: watch for hepatitis and myelosuppresson (CBC/liver panel every 2 weeks for 3 months)
-mycophenolate mofetil: watch for GI effects
-cyclosporine: transient GI side effects
cats:
1. monotherapy with glucocorticoids is mainstay
-prednisolone oral
-dexamethasone
- use steroid-sparing immunosuppressants to achieve clinical remission earlier and for more long term control:
-cyclosporine: transient GI side effects
-chlorambucil
-mycophenolate mofetil
horses: need high doses of steroids = bad news bears
1. oral prednisolone or dexamethasone or topical glucocorticoid sprays
- limited steroid -sparing choices
-azathioprine: low aborption and short half life = low effect
-mycophenolate mofetil: need low doses and frequent monitoring for myelosuppression, hepatotoxicity, GI signs, others
describe the diagnostic approach to superficial pustules in dogs, cats, and horses
- prick the pustule, collect pus, and examine microscopically
- if needed, treat with anx/antiseptics
- if needed: perform bacterial culture of content from pricked pustule
- if needed, obtain a biopsy from an entire intact pustule
