Skin and Soft Tissue Flashcards
What are the skin compartments?
Epidermis, dermis, subcutaneous fat, fascia and muscle
What are the infection sites of the skin?
Impetigo - epidermis
Folliculitis - hair follicle
Erysipelas - deeper in skin
What are things to consider about the host?
Diabetes leading to neuropathy and vasculopathy
Immunosuppression
Renal failure
Milroy’s disease - lymphoedema of lower limbs
Predisposing skin conditions
Describe impetigo
Superficial skin infection
Multiple vesicular lesions on erythematous base
Golden crust is highly suggestive of diagnosis
Highly infectious
What most commonly causes impetigo?
Staph. aureus
Less common - strep pyogenes
What are predisposing factors for impetigo?
Skin abrasions, minor trauma, burns, poor hygiene, insect bites, chickenpox, eczema and atopic dermatitis
Where does impetigo mainly occur?
Exposed parts of body including face, extremities and scalp
Common in children 2-5 years
What is the treatment for impetigo?
Small areas can be treated with topical antibiotics alone
Large need topical treatment and oral antibiotics - flucloxacillin
Describe erysipelas
Infection of the upper dermis
Painful, red area with associated fever
Regional lymphadenopathy and lymphangitis
Distinct elevated borders
High recurrence rate
What is erysipelas most commonly due to?
Strep pyogenes
Where does erysipelas mainly involve?
70-80% of cases involve lower limbs and 5-20% effect face
Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis and DM
Describe cellulitis
Diffuse skin infection involving deep dermis and subcutaneous fat
Presents as spreading erythematous area with no distinct borders
Fever is common
Regional lymphadenopathy and lymphangitis
Possible source of bacteraemia
What is cellulitis most commonly due to?
Strep pyogenes and staph aureus
Gram negatives in diabetics and febrile neutropenic
What are some predisposing factors of cellulitis?
DM, tinea pedis (athletes foot) and lymphoedema
Patients can have lymphangitis and/ or lymphadenitis
What is the treatment for erysipelas and cellulitis?
Combination of anti-staphylococcal and anti-streptococcal antibiotics
In extensive disease - admission for IV antibiotics and rest
What are some hair assocated infections?
Folliculitis, furunculosis and carbuncles
Describe folliculitis
Circumscribed, pustular infection of a hair follicle
Up to 5mm in diameter
Present as small red papules
Central areas of purulence that may rupture and drain
Constitutional symptoms not often seen
Where is folliculitis mainly found?
Head, back, buttocks and extremities
What is the most common organism causing folliculitis?
Staph aureus
Benign condition
Describe furunculosis
Referred as boils
Single hair follicle associated inflammatory nodule extending into dermis and subcutaneous tissue
Usually affected moist, hairy, friction prone areas of skin
May spontaneously drain purulent material
What are the risk factors and causes for furunculosis?
Obesity, DM, atopic dermatitis, chronic kidney disease and corticosteroid use
Staph aureus
Describe carbuncle
Occurs when infection spreads to involve multiple furuncles
Multiseptated abscesses and purulent material may be expressed from multiple sites
Constitutional symptoms common
Neck, posterior trunk or thigh
What is the treatment of hair associated infections?
Folliculitis - no treatment or topical antibiotics
Furunculosis - no treatment. If not improving then oral antibiotics
Carbuncles - hospital admission, surgery and IV antibiotics
What are predisposing conditions for necrotising fasciitis?
DM, surgery, trauma, peripheral vascular disease and skin popping
What is type I necrotising fasciitis?
Refers to mixed aerobic and anaerobic infection
Typical organism - strep, staph, enterococci, gram negative bacilli and clostridium
What is type II necrotising fasciitis?
Monomicrobial
Normally associated with strep pyogenes
Describe necrotising fasciitis
Rapid onset
Anaesthesia at site of infection is highly suggestive
Systemic features - fever, hypotension, tachycardia, delirium and multiorgan failure
What does necrotising fasciitis present as?
Sequential development of erythema, extensive oedema and severe and unremitting pain
Haemorrhagic bullae, skin necrosis and crepitus
What is the treatment for necrotising fasciitis?
Flucloxacillin, gentamicin and clindamycin - broad spectrum antibiotic
Mortality between 17-40%
Describe pyomyositis
Purulent infection deep within striated muscle, often manifesting as abscess
Infection is secondary to seeding into damaged muscle
Common sites - thigh, calf, arms, gluteal region, chest wall and psoas muscle
How does pyomyositis present?
Fever, pain and woody induration of affected muscle
If untreated can lead to septic shock and death
What ae predisposing factors for pyomyositis?
DM, HIV/ immunocompromised, IV drug use, rheumatological disease, malignancy and liver cirrhosis
What is the commonest cause of pyomyositis?
Staph aureus
Others include gram positive/ negative, TB and fungi
What is the investigation and treatment for pyomyositis?
CT/ MRI
Drainage with antibiotic cover on gram stain and culture results
Describe septic bursitis
Small sac like cavities that contain fluid and lined by synovial membrane
Located subcutaneously between bony prominences or tendons
Facilitate movement with reduced friction
Patellar and olecranon
What are predisposing factors for septic bursitis?
Rheumatoid arthritis, alcoholism, DM, IV drug abuse, immunosuppression and renal insufficiency
Infection is often from adjacent skin infection
How does septic bursitis present?
Peri bursal cellulitis, swelling and warmth
Fever and pain on movement
Diagnosed by aspiration of fluid
What is the most common cause of septic bursitis?
Staph aureus
Rarer - gram negative, mycobacteria and brucella
Describe infectious tenosynovitis
Infection of synovial sheets that surround tendons
Flexor associated tendons and tendon sheets of hand most common
Penetrating trauma is most common inciting event
What is the most common cause for infectious tenosynovitis?
Staph aureus and streptococci
Chronic infections may be due to mycobacteria and fungi
Possibly disseminated gonococcal infection
How does infectious tenosynovitis present?
Erythematous fusiform swelling of finger
Held in semi-flexed position
Tenderness over length of tendon sheat and pain with extension of finger is classical
What is the treatment for infectious tenosynovitis?
Empiric antibiotics
Hand surgeon to review ASAP
Describe toxin-mediated syndromes
Group of pyrogenic exotoxins
Do not activate immune system via normal contact between APC and T cells
Super antigens bypass this and attach directly to T cell receptors activating them
Massive cytokine release - endothelial leakage, haemodynamic shock and multiple organ failure
What is toxin-mediated syndromes mainly caused by?
Staphylococcus aureus and streptococcus pyogenes
S. aureus - TSST1, ETA and ETB
S. pyogenes - TSST1
What can cause toxic shock syndrome?
High absorbency tampons during menses
Staph aureus secreting TSST1 small skin infections
What is the diagnosis criteria for staphylococcal TSS?
Fever, hypotension, diffuse macular rash, 3 organs involved - liver, blood, renal, GI, CNS and muscular, isolation of S. aureus from mucosal or normal sterile sites, production of TSST1 by isolate and development of antibody to toxin
What is the treatment for streptococcal TSS?
Urgent surgical debridement of infected tissues
Mortality higher then staph
What is streptococcal TSS associated with?
Presence of streptococci in deep seated infections such as erysipelas or necrotising fasciitis
What is the treatment for TSS?
Remove offending agent, IV fluids, inotropes, antibiotics and IV immunoglobulins
Describe staphylococcal scalded skin syndrome
Infection due to particular strain of S. aureus producing toxin A or B
Characterised by widespread bullae and skin exfoliation
Usually occurs in children but rarely in adults
What is the treatment for staphylococcal scalded skin syndrome?
IV fluids and antimicrobials
Mortality is 3% in children but higher in adults who are immunocompromised
Describe Panton-Valentine leucocidin toxin
Gamma haemolysin
Transferred from one strain of S. aureus to another including MRSA
Can cause SSTI and haemorrhagic pneumonia
Tends to affect children and young adults
Recurrent boils which are difficult to treat
What is the treatment for Panton-Valentine leucocidin toxin?
Antibiotics that reduce toxin production
Describe IV catheter associated infections
Nosocomial infection
Normally starts as local SST inflammation progressing to cellulitis and tissue necrosis
Common to have associated bacteraemia
What are the risks for IV catheter associated infection?
Continuous infusion over more than 24hrs
Cannula in situ for more than 24hrs
Cannula in lower limb
Patients with neurological/ neurosurgical problems
What is the main cause of IV catheter associated infection and how is it diagnosed?
Staph aureus
Commonly forms a biofilm which then spills into bloodstream and can seed to other places
Diagnosis - clinically or positive blood cultures
What is the treatment for IV catheter associated infection?
Remove cannula and express any pus from thrombophlebitis
Antibiotics for 14 days
Echo
Prevention is most important
What is the classification of surgical wounds?
Class 1 - clean wound
Class 2 - clean contaminated wound
Class 3 - contaminated wound
Class 4 - infected wound
What are some causes for surgical site infections?
Staph. aureus, coagulase negative staphylococci, enterococcus, Escherichia coli, pseudomonas aeruginosa, Enterobacter, streptococci, fungi and anaerobes
What are the risk factors for surgical site infection?
Diabetes, smoking, obesity, malnutrition, concurrent steroid use and colonisation with staph. aureus
What are procedural factors for surgical site infections?
Shaving of site the night prior
Improper preoperative skin prep
Improper antimicrobial prophylaxis
Break in sterile technique
Inadequate theatre ventilation
Perioperative hypoxia
What is the investigations and treatment for surgical site infections?
Importance of sending pus/ infected tissue for culture
Avoid superficial swabs and aim for deep structures
Antibiotic to target likely organism
What infections need urgent attention?
Necrotising fasciitis, pyomyositis, TSS, PVL infections and Venflon associated infections
