SSTI Flashcards
Epidemiology & Predisposing RF Cellulitis
Middle-aged and older individuals
Skin barrier disruption 2/2 trauma, skin inflammation (eczema, radiation), edema (impaired lymphatic drainage - surgery, venous insufficiency), obesity, immunosuppression, pre-existing skin infection, MRSA exposure
MC Etiology Non-purulent Cellulitis
Beta-hemolytic strep - group A (S. pyogenes)
Purulent cellulitis = MRSA
Epidemiology Erysipelas
Young children and older adults
MC Etiology Erysipelas
Beta-hemolytic strep
MCC Skin abscess
S. aureus (MSSA or MRSA) - 75%
MRSA risk factors
Healthcare: Recent hospitalization, residence in long term care, recent surgery, hemodialysis
RF : HIV infection, IVDA, prior abx use, incarceration, military service, sharing sports equipment, sharing needles, razors, other sharp objects
CP Cellulitis
Skin erythema, edema, warmth that develops 2/2 bacterial entry into breaches in skin barrier +/- fever (more local sx than erysipelas)
Almost ALWAYS unilateral
MC site = lower extremities
+/- regional LAD & lymphangitis
+/- dimpling of skin 2/2 edema = “peau d’orange”
Severe infection w/ severe systemic sx = investigation for additional underlying sources of infection - streptococcal toxic shock syndrome
Causes of recurrent cellulitis
Inter-digit toe spaces w/ fissuring or maceration, tinea pedis, or chronic venous insufficiency for any reason
Cellulitis involves which skin layers?
Deeper dermis & SC fat
Erysipelas involves which layers of skin?
Upper dermis & superficial lymphatics
CP Erysipelas
Acute onset sx w/ systemic manifestations - fever, chills, severe malaise, headache (sys sx can precede local inflammatory si/sx by hours)
CLEAR demarcation btwn involved & uninvolved tissue. Classic “butterfly” involvement of face. Involvement of ear ‘ classic “Milian’s ear sign” (ear has no deeper dermis or SC fat)
Cellulitis w/ gangrenous appearance + crepitant is more likely 2/2
Clostridia & other anaerobes
Skin abscesses involve which layers of skin?
Clinical presentation skin abscess
Collection of pus within dermis or SC space with or without surrounding cellulitis
Abscess can be 2/2 deep infection of hair follicle (furuncle/boil) which can coalesce into carbuncle - common areas = back of neck, face, axillae, buttocks
Fever, chills, and systemic toxicity are unusual - more likely if large carbuncle
Complications of cellulitis & abscess
Bacteremia, endocarditis, osteomyelitis, sepsis, toxic shock syndrome
Diagnosis of erysipelas, cellulitis, skin abscess
Clinical diagnosis based on clinical manifestations -
Cellulitis & Erysipelas: Erythema, edema, and warmth.
Erysipelas - clearly demarcated & SYSTEMIC SX
Cellulitis - no clear borders, systemic sx more rare (except possible fever)
Skin abscess - painful, fluctuant, erythematous nodule w/wo surrounding cellulitis
Treatment abscess
Incision and drainage w/ culture and susceptibility testing
Blood cultures (BEFORE ABX) NOT necessary UNLESS:
- Systemic toxicity
- Extensive SSTI
- Persistent cellulitis
- Special exposures (animal bite, water-associated injury)
- Underlying co-morbidities (lymphedema, malignancy, neutropenia, immunodeficiency, splenectomy, DM)
When to order imaging on abscess and what kind of imaging to order?
Reason: To determine if abscess if present - order ULTRASOUND
What type of imaging to order to determine cellulitis vs osteomyelitis?
MRI
Imaging cannot distinguish between cellulitis and _____ and imaging should not delay ______ intervention if there is clinical suspicion for the latter
Imaging cannot distinguish between cellulitis and NECROTIZING FASCIITIS/GANGRENE and should not delay SURGICAL intervention (debridement) if there is clinical suspicion for the latter
Differential diagnosis cellulitis - three can’t miss dx
Cellulitis is often confused w/ other infectious or non-infectious illnesses -
Rapidly progressing signs of systemic toxicity - should prompt consideration of severe infection, including:
- Necrotizing fasciitis -
Deep infection = progressive destruction of muscle fascia - erythema, swollen, warm - key = PAIN OUT OF PROPORTION TO EXAM FINDINGS - dx established w/ visualization of fascial planes (surgical) - Toxic shock syndrome -
Pain precedes physical findings. Si/sx regular SSTI…but THEN ecchymosis & sloughing of skin + fever. Go from normotensive to hypotensive. - Gas gangrene -
Fever & severe pain in extremity AFTER recent surgery/trauma. + crepitus = clostridial infection - can be detected radiographically.
Cellulitis differential diagnosis
Can’t miss: necrotizing fasciitis, TSS, gas gangrene
Other infectious dx:
Erythhema migrans, herpes zoster, septic arthritis, septic bursitis, osteomyelitis, mycotic aneurysm
Other non-infectious dx:
DVT, contact dermatitis, acute gout, drug reaction, vasculitis, insect bite, vaccination site reaction
How to tell cellulitis/erysipela vs erythema migrans of Lyme disease
The rash of Lyme disease is not painful, has slow progression, and is associated with less marked fever than erysipelas.
A targetoid lesion with central clearing is sometimes present.
There may be a history of recent travel to endemic areas and a recent tick bite. Lyme exposure tends to occur in the spring or summer
CP Cellulitis overlying a septic joint
Septic arthritis - cellulitis can overly a septic joint - manifests as joint pain, swelling, warmth and LIMITED ROM of joint - dx based on synovial fluid examination
How to tell cellulitis vs osteomyelitis
Osteomyelitis may underlie an area of cellulitis
Cellulitis that’s not getting better w/ appropriate abx therapy - investigate further & get imaging to r/o osteo - MRI or plain film
