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
Cellulitis vs herpes zoster d/dx
Although less common, cellulitis can have vesicles & bullae
Herpes is along ONE dermatome. Erythematous papules that evolved into grouped vesicles. Dx via PCR.
Irritant contact dermatitis vs cellulitis
Irritant contact dermatitis = PRURITIC & reaction is limited to site of contact & a/w burning, stinging
Cellulitis vs acute gout
Acute gouty arthritis consists of severe pain, warmth, erythema, and swelling overlying a SINGLE joint, prior attacks etc
Dx: Synovial fluid analysis - Sodium urate crystals of gout (needle shaped, strong negative bifringence) or pseudogout (CPPD rhomboid, positive bifrinegence)
Skin lesions that need to be distinguished from skin abscess
Epidermoid cyst
Folliculitis
Hidradenitis supprativa
Nodular lymphangitis
