Theme 10 - clinical infections in skin tissues Flashcards
What are the functions of the skin?
Physical barrier - chemicals, UV, microorganismsand chemical agents
Homeostasis - thermoregulation via sweating
Immunological function - Ag presentation and phagocytosis
Microbiology of the skin
Heavily colonised organ
Coagulase - negative staphylococci like Staph Aureus
other examples include:
- propionbacterium
- corynebacterium spp
Pathogenesis of the skin - localised infection
Penetration of skin with a contaminated object
Accidental, e.g. tooth, rusty nail, knife etc.
Deliberate, e.g. surgical procedure, therapeutic injection, injection drug use
This can cause contamination of pre-existing break in the skin surface e.g. abrasion, athlete’s foot
neuronal migration of herpes complex is another route of infection too
Pathogenesis of the skin - 2 examples of systemic/generalised infection
chickenpox
meningococcal sepsis
What are viral warts, what are they caused by and how do they cause symptoms?
Small asymptomatic growths of skin (hands, genitals, feet, around nails, throat)
Causative agent: Human Papilloma Virus (HPV)
Pathogenesis: cause proliferation and thickening of stratum corneum, granulosum and spinosum
Clinical presentation of viral warts, how are they treated and how can they be prevented?
Clinical presentation:
asymptomatic, mechanical,
or cervical cancer sign (HPV cause)
Treatment:
Topical- salicylic acid,
silver nitrate, cryosurgery
Prevention:
Gardasil (types 16, 18, 6 and 11);
(16 and 18 cause 70% cancer)
Genital: Barrier protection e.g. condoms
What is a Pilonidal Cyst or Abscess?
cyst in natal cleft
caused by ingrown hair
contain hair and debris
discharge to form sinus
can present with pain, swelling and pus
how is a Pilonidal Cyst or Abscess treated?
Hot compress, analgesia and antibiotics
Surgical excision
What is impetigo, how does it present?
Crusting around the nares of the mouth in superficial skin
Caused by Staph aureus and is transmissible
How is impetigo treated?
Topical antiseptics
Oral antibiotics
What is Erysipelas?
Rash over face, raised, demarcated
Occurs in the upper dermis
Can involve lymphatics- systemic disease
Causative organism:
Strep pyogenes
Cellulitis - what is it and what causes it?
Infection affecting the inner layers of the skin
Infection spreads from dermis and subcutaneous fat, into lymphatics Causative agent: Bacterial Staph aureus, Group A Streptococci (Strep pyogenese), other B-haemolytic Streptococci
Pathogenesis of cellulitis
Bugs enter through breaks in skin
Wound, insect bite
Pre-existing condition eg. eczema,
Athletes foot, shingles (Zoster) etc.
Clinical presentation of cellulitis
Rubor (red), calor (heat), dolor (pain), tumor (swelling)
Loss of skin creases, blistering, pus/exudate, fever
how is cellulitis diagnosed? how is it treated?
Clinical, unless septic cultures rarely helpful
Exclude other causes of red hot swollen leg (eg. DVT
treated by elevation, rest, antibiotics and drainage of pus
What is orbital cellulitis?
Infection of soft tissues around and behind eye
pathogenesis of orbital cellulitis…
from skin or sinuses or haematogenous or trauma
clinical presentation of orbital cellulitis
Erythema, swelling with induration
and pain on eye movement and bulging
causative organism of orbital cellulitis and treatement
S. aureus, S. pyogenes but also
S. pneumoniae and H. influenzae
IV antibiotics
What is necrotising fascitis?
“flesh eating bug”
There are 4 types:
Type 1: Synergistic/poly-microbial, host impairment- gram negatives,
Streps, anaerobes
Risk factors include: Diabetes, obesity, immunosuppression, alcohol, older age group- eg. Fournier gangrene
Type 2: Group A Strep (S. pyogenese) mediated
Risk factors include:
younger age group, associated with cut or injury
Type 3:
Vibrio vulnificus-
sea water, coral
Type 4: fungal
what is the pathogenesis of necrotising fasciitis?
Type 1:
ischaemic tissue, colonisation then infection resulting in further ischaemia and necrosis
Eg. diverticulitis, Fournier
Type 2:
- infection, toxin release
- disruption in blood supply
- necrosis
clinical presentation of necrotising fasciitis?
Swelling, erythema (non confluent),
pain (out of context)
Crepatus, sepsis/toxaemia, necrosis, “dish water” exudate
Necrosis makes skin appear a very dark purple/red across the span of the limbs
treatment for necrotising fasciitis
Surgical emergency, debridement and antibiotics
What is gangrene?
What are the risk factors?
necrosis caused by inadequate blood supply
RISK FACTORS:
- atherosclerosis
- smoking
- Diabetes
- Autoimmune disease
What are the different types of gangrene?
Dry” vs. “Wet” Gangrene vs. “Gas” Gangrene
Pathogenesis of gangrene
Poor blood flow- tissue necrosis- colonisation- infection- synergistic infection- further necrosis
Clinical presentation of gangrene (for each type - dry, wet and gas gangrene)
Dry- “mummified”, auto-amputate
Wet- boggy, swollen “dactylitis”, exudate, surrounding erythema
Gas- as above but with gas in tissue- crepitus
What causes gangrene?
Skin (Staphs, Streps);
Enteric (GNB, Anaerobes inc. Clostridium)
Treatment of gangrene
Surgical: source control (drainage of exudate) and
revascularisation
Antibiotics
What is diabetic foot infection?
Spectrum of disease from superficial through to deep bone infection in patients with Diabetes
Pathogenesis of diabetic foot infection
Damage to blood vessels -
Ischaemia, impaired immunity
and poor wound healing
Damage to nerves-
Neuropathy, trauma
High blood sugars-
prone to bacterial infection
Causative organisms of DFI
Superficial- skin flora: Staph aureus, Streps, Corynebacterium
Deeper- skin and enteric flora: above + GNB, anerobes
Treatment of DFI
Surgical debridement Revascularisation Antibiotics off-loading Diabetic control
Pathogenesis of osteomyelitis (the 3 routes of spread)
Contiguous: eg. Diabetic foot infection
Haematogenous: bugs in bloodstream
Penetrating: peri-prosthetic, traumatic
Acute vs. Chronic osteomyelitis
acute:
inflammatory reaction e.g. sepsis
chronic:
more than a month
acute flares that smoulder
resulting in bone death and new bone formation
new bone formation is called
involucrum
bone death is called
sequestrum
causative organisms of osteomyelitis relative to each route of pathogenesis
Haem- (children): S. aureus, Strep, Kingella, Haemophilus
Contiguous: Skin (Staph, Streps) enteric (GNB, anaerobes)
Penetrating: surgical- skin flora, open fracture- skin, environment
Sickle cell: Salmonella sp.
Septic Arthritis - what is it?
Infection of the joint (usually bacterial but can also be cause by viruses, mycobacterium and fungi)
pathogenesis of septic arthritis
Pathogenesis:
Haematogenous: blood stream infection
Local spread: soft tissue, bone, bursitis
Penetrating: joint injections, surgery, trauma
causative organisms of septic arthritis
Causative organisms: S. aureus, Streps, Haemphilus, N. gonorrhoeae, E.coli
clinical presentation of septic arthritis and diagnosis
Pain, swelling, erythema, reduced range of movement (unable to weightbear), Sepsis
diagnosis confirmed by joint aspiration
septic arthritis is treated by
Antibiotics (guided by cultures)- 4 to 6 weeks
Surgical source control: Joint washout
what is prosthetic joint infection?
infection of tissue and bone surrounding a prosthetic joint
pathogenesis of prosthetic joint infection
Pathogenesis:
Bugs get onto surface of foreign body (prosthetics) immune system cannot reach- establishment of biofilm (slime) occurs
Early: Implanted at time of surgery or shortly after (via wound)
Late: Haematogenous but can be late presenting Early infections
Causative organisms of prosthetic joint infections
Early:
Staph aureus, Staph epidermidis, Propionibacterium
Late: Above and E. coli, B Haem Streps, Viridans Streps
Clinical presentation of PJI
pain
instability
swelling
sinus and pus formation
treatment of PJI
Antibiotics alone
Antibiotics with debridement
Single-stage revision:
remove infected joint and
replace with new one at same operation
Two- Stage revision:
Remove old joint, given 6 weeks of antibiotics, insert new joint when sure all infection settled
How is Syphilis transmitted and what is the causative agent?
Sexually transmitted infection
Caused by Treponema pallidum
Primary syphilis presents as a chancre which is…
painless, firm non-itchy ulcer
at the point of contact e.g. penis tip
Usually solitary
Lasts 3-6 weeks
Lymphadenopathy
Secondary syphilis presents as
4-10 weeks after primary
Symmetrical rash that is pink, itchy and is found everywhere (even mucous membranes and soles/palms of hands and feet)
- Maculo-papular or pustular
- Rash contains Treponema
Tertiary syphilis presents as
3 to 15 years after initial infection in 3 forms:
Gummatous,
Neuro,
Cardiovascular
Gummatous is can be chronic causing large inflammatory swellings of skin, bone and liver.
