L07 - Infections of the skin, soft tissues, bones, and joint Flashcards
4 crude layers of the skin?
Epidermis
Dermis
Subcutaneous tissue
Deep fascia
What are the more common infection sites out of skin, bone, joint and soft tissues?
Skin and soft tissue infection are most common
List 4 defense mechanisms of the skin?
■ Normal integrity of the skin. ■ Rapid cell turnover. ■ Normal flora of the skin. ■ Antimicrobial effect: a) lipid layer (sebum-derived) of normal skin b) Mild acidity c) Antimicrobial peptides
What type of bacteria make up majority of normal skin flora?
Mostly gram +ve
Most abundant = Staphylococcus (primarily coagulase-negative staphylococci i.e Staph. epidermidis)
Corynebacterium spp.
Propionibacterium acnes
Micrococcus spp.
What are other less common skin flora organisms?
Gram-negative bacilli (e.g. Acinetobacter, Pseudomonas, other non-fermenters) @elderly, hospitalized
Yeasts (e.g. Candida, Malassezia furfur) @ moist area of body
What factors can influence the make up of skin flora?
– Age – Body location – Occupation – Hospitalization – Medications – Diseases (local and systemic)
What are the 4 pathways in the pathogenesis of skin infections?
- Breach of normal integrity of skin (e.g. trauma / abrasions, iatrogenic (surgery, intravenous catheter))
- Alteration of normal skin flora
- Changes in local environment of tissues, e.g. Presence of devitalized tissues; in surgical wounds: haematoma, foreign bodies, etc.
- Introduction of pathogenic exogenous (e.g. Vibrio from seawater; dog bites) / endogenous microbial flora
What is the name of ringworm infection?
Dermatophytosis
caused by fungi, named based on appearance, no worms involved.
Define dermatophytosis?
Infection of keratinized tissues by keratinolytic dermatophytic fungi / mould
List 3 organisms that can cause dermatophytosis?
All 3 are moulds
Trichophyton spp.
Microsporum spp.
Epidermophyton floccosum
Difference between dermatophytosis and dermatomycoses?
Dermatophytosis = infection by keratinolytic dermatophytic fungi
Dermatomycoses = infection by non-dermatophytic fungi
How do dermatophytic moulds survive on skin?
feed on keratin of skin, hair, skin appendages to obtain nutrients
Explain the diagnostic tests for dermatophytosis?
1) KOH wet mount (dissolves keratin to expose fungus. Hyaline fungal strands can be seen)
2) Fungal culture (long time)
What is the clinical presentation of dermatophytosis?
1) Skin: ring-like wound (edge more inflamed, centre heals with time)
2) Hair: more brittle, falls easily
3) Nail: surrounding skin may have bacterial infection
Causative pathogen and clinical presentation of impetigo?
Bacterial infection of skin by Staphylococcus aureus (or rarely Streptococus pyogenes) by direct contact
Begin as small macule/ intraepidermal abscesses near nose or mouth, evolve into larger lesion with honey-colored crust of dried serum
What is the morphology and location of Carbuncles?
large, contiguous groups of furuncles
Commonly at the back / trunk region
What is the epidemiology of carbuncles?
Mainly affect:
Elderly, hospitalized
Diabetic
Immunocompromised patients (e.g. Pseudomonas aeruginosa)
What is the morphology of Furuncle?
Furuncles = boils
- Painful, deep subcutaneous abscess around hair follicle
- Rupture of skin can release pus inside
What is infected in Cellulitis? What are the causative pathogens?
acute skin infection spreading, extending to involve subcutaneous tissues
– Beta-haemolytic strep/ Group A strep/ Streptococcus pyogenes (common)
– (Staphylococcus aureus - rare)
– Vibrio, Enterobacteriaceae, other Gram negative bacilli.
Clinical presentation of cellulitis?
1) Local region of inflammation (redness, swelling) with ill-defined margin
2) ± local abscess
3) Fever, chills, bacteraemia
What are common types of Pyoderma?
Impetigo
Folliculitis
What is the pathology and causative pathogen of Erysipelas?
Form of cellulitis but is not cellulitis
mostly caused by beta-haemolytic streptococci/ Group A Strep.
Marked subepidermal oedema with Heavy infiltration of neutrophils
Clinical presentation of Erysipelas?
1) Very painful
2) Red lesions with distinct border
3) Spreads rapidly
4) Classically affects the face (MALAR rash), lower limbs of elderly, diabetic patients
What is Paronychia and what causes it?
superficial infection of the nail fold
Acute cause: Staphylococcus aureus
Chronic cause: (moist hands, e.g. housewife, wet market): Candida spp. (e.g. Candida albicans)
Clinical presentation of Paronychia?
Rapid onset of erythema, edema, and tenderness at proximal nail folds
What is the most urgent form of cellulitis?
Peri-orbital cellulitis
Around eyelids, possible intra-orbital or intra-ocular involvement
Need aggressive therapy
What is the treatment for MSSA infections?
Methicillin-sensitive Staphylococcus aureus
Use:
1) Cloxacillin (penicillin, β-lactamase-resistant);
2) Augmentin
3) 1st generation cephalosporins (cefadroxil, cefalexin)
What are the 2 types of MRSA?
Hospital-acquired MRSA (HA-MRSA)
Community-associated MRSA (CA-MRSA)
What is the typical presentation of CA-MRSA?
soft tissue abscess formation (e.g. furuncles, carbuncles)
Occasionally present as necrotizing pneumonia (fulminant, rapidly fatal) in young individuals
What are the unique features of CA- MRSA compared to HA-MRSA?
CA-MRSA:
1) Possess Panton-Valentine leukocidin toxin (kills white blood cells)
2) not multi-resistant towards antibiotics, Resistant to most beta-lactam, but susceptible to other agents, e.g. clindamycin
What type of infection involves Dermis, subcutaneous fat, deep fascia, muscle?
necrotizing soft tissue infections
Name 2 forms of necrotizing soft tissue infection?
Clostridial myonecrosis (gas gangrene)
Necrotizing fasciitis (most common)
Types of necrotizing fasciitis and their causative agents?
Type I = Mixed gut flora: Anaerobic bacteria(e.g. Bacteroides)
+ facultatively anaerobic bacteria (e.g. streptococci, Enterobacteriaceae)
Type II: Streptococcus pyogenes (Group A) ± other organisms
Type III: Vibrio spp. (esp Vibrio vulnificus) + related spp. (e.g. Aeromonas spp.)
Type I necrotizing fasciitis occurs in which patients?
- After intra-abdominal/ pelvic surgery
- Arise de novo in perineal area»_space; Fournier’s gangrene @ scrotum of elderly
Type III necrotizing fasciitis occurs after what exposure?
Exposure to contaminated water
Consumption of contaminated seafood
Clinical presentation of necrotizing fasciitis?
Fever
severe pain due to nerve damage: Tenderness at spreading edge of lesion, central part becomes anaesthetic (lost of sensation)
Edema
Thrombosis of blood vessels cause ishaemis: DUSKY BLACK NECROSIS of skin
Causative agent of Clostridial myonecrosis?
85-90%: Clostridium perfringens
Sometimes: other Clostridium spp.
Can be mixed with facultative anaerobic bacteria (e.g. Enterobacteriaceae
Pathogenesis of Clostridial myonecrosis?
muscle injury + contamination with soil / other foreign materials containing spores of Clostridium perfringens
> > coagulative necrosis of muscle fibres (infarcted, acidophilic, opaque ‘tombstone’, lost nuclei)
Clinical presentation of Clostridial myonecrosis?
- Locally, tense oedema, serosanguineous/ yellowish with small amounts of blood
- Foul odour of the wound
- Crepitus
Name of infection causing abscess formation in skeletal muscle by Staphy. aureus?
Pyomyositis
What muscle is common infected secondary to osteomyelitis of the spine?
Psoas muscle @ psoterior body wall
Psoas abscess
How does body location of surgery affect the risk of post-op infections?
Clean (e.g. brain, joint) Clean contaminated Contaminated Dirty (e.g. perforated large intestine)
The more dirty, the higher the risk of post- op infections
Clinical presentation of surgical wound infections?
1) Purulent drainage (pus) from the incision
2) Pain, tenderness, localized swelling, redness, dehiscence of wound
3) Fever (sometimes)
List some bacteria expected to cause post-op infection in pelvic and abdominal surgery?
E. coli, Proteusspp., Klebsiella spp., etc.
Streptococci, enterococci; anaerobes.
List some bacteria expected to cause post-op infection in Orthopaedic and neuro surgery?
S. aureus, coagulase-negative staphylococci
List some bacteria expected to cause post-op infection by nosocomial infection?
Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia; Candida albicans
What is the extent of involvement in osteomyelitis?
infectious process involving the various components of bone, viz. periosteum, medullary cavity, and cortical bone.
3 types of osteomyelitis?
■ Acute osteomyelitis.
■ Chronic osteomyelitis.
■ Osteomyelitis associated with prosthetic implants
What is the main mode of spread for osteomyelitis?
Haematogenous
Pathology of Chronic osteomyelitis?
- Acute inflammation: Increased pressure in Haversian system»_space; compression on / obliteration of vascular channels»_space; ischaemia and bone necrosis
- Subperiosteal extension of infection lifts periosteum away from bone»_space; new bone formation
- Ischaemic segments of bone separate to form the sequestrum (= piece of dead bone; hallmark of chronic osteomyelitis)
What is the hallmark feature of chronic osteomyelitis?
sequestrum (= piece of dead bone)
Causative agent for acute haematogenous osteomyelitis?
Generally monomicrobial infection
Commonest: Staphylococcus aureus
Streptococcus agalactiae/ pyogenes
Escherichia coli, Haemophilus influenzae
Level of involvement in acute vertebral osteomyelitis?
Segmental arteries from aorta supplying vertebrae bifurcates to supply 2 adjacent bony segments
> > involves 2 adjacent vertebrae and the intervertebral disk.
What are some predisposing factors of contiguous focus osteomyelitis?
– Trauma, surgical operations of bones, open fractures, chronic soft tissue infections.
– Vascular insufficiency, e.g. diabetes mellitus.
Difference between acute haematogenous osteomyelitis and Contiguous focus osteomyelitis?
Acute = monomicrobial, primary infection by blood bourne pathogen
Contiguous = polymicrobial, Secondary infection from adjacent soft tissue infection
Apart from 3 types of osteomyelitis, what is another group of bone infections?
Skeletal mycobacterial infection
Types of Skeletal mycobacterial infection
and their causative agents?
Tuberculosis
Non-tuberculosis mycobacteria: M. marinum, M. aviumcomplex, M. fortuitum
Clinical presentation of Contiguous focus osteomyelitis?
Fever, chills
Leukocytosis
Pain, local swelling
Signs, symptoms may be minimal or non-specific in some patients, e.g. infants, IV drug addicts.
Clinical presentation of Chronic osteomyelitis?
Local bone loss
Local abscess / adjacent soft tissue inflammation, persistent drainage
Sinus tract formation (= opening of skin connecting to abscess)
Chronic pain
May have low-grade fever
Pathogenesis of Prosthesis-related osteomyelitis?
– Early: introduced during operation or from post-operative wound infection.
– Late: haematogenous
What usually precedes Mycobacterium TB osteomyelitis?
contiguous lymphadenitis
Usually from haematogenous spread during primary infection»_space; chronic osteomyelitis
What people are typically infected by M. marinum caused osteomyelitis?
Typically in persons with recreational / occupational exposure to seawater
cause skin lesions / tenosynovitis (inflammation of tendon sheath)
How to examine osteomyelitis?
Best option:
- Magnetic resonance imaging (MRI)
Others:
- CT
- Radionuclide imaging: PET
a) Bone scan
b) Gallium scan
How to make Microbiological diagnosis of osteomyelitis?
– Blood culture.
– Biopsy of the bone lesion.
– In chronic osteomyelitis, culture of sinus tract is not reliable for predicting the organisms causing osteomyelitis.
Treatment of osteomyelitis?
Antibiotic: need prolonged course
May need surgical débridement (especially chronic osteomyelitis: must remove sequestrum (dead bone))
Drain abscess
Which part of the body is affected by Infective arthritis and why?
Synovium of larger joints: knee, hip, shoulder, ankle, elbow; but any joint can be involved
highly vascular, lacks basement membrane = susceptible to bacterial seeding
Route of spread of infective arthritis?
Haematogenous seeding
Direct inoculation (e.g. open wound, percutaneous needle drainage)
Pathogens causing Polyarthritis infective arthritis?
- Viruses
- Neisseria gonorrhoeae (disseminated gonococcal infection)
Clinical features of Infective arthritis?
Pain, limitation of movement at the joint
Fever, joint swelling; leukocytosis
What autoimmune diseases can cause polyarthritis?
Rheumatoid arthritis, systemic lupus erythematosus, diabetes mellitus
Common causative agents of acute bacterial arthritis?
Staphylococcus aureus = the commonest pathogen
Neisseria gonorrhoeae (in sexually active)
Gram -ve bacilli in elderly/ immunocompromised
Staph. aureus, Pseudomonas aeruginosa (in IV drug addicts)
Haemophilus influenzae B in children under 2
Clinical presentation of acute bacterial infective arthritis?
Usually pain, swelling, limited ROM at Larger joints
Smaller joints affected = think Neiserria gonorrheoae
Fever and Leukocytosis present
What diseases must be differentiated from infective arthritis?
Rheumatoid arthritis
Crystal -induced arthritis i.e. gouty arthritis by monosodium crystal or Pseudogout by CCP crystal
Trauma, OA or tumour
What tests can be done to differentiate infective arthritis from other causes of joint pathology?
■ Blood culture
■ Diagnostic synovial fluid aspirate – Leukocyte count, crystals, Gram stain, culture.
■ Synovial biopsy
If a patient has monosodium urate crystal from synovial aspirate and positive bacteria culture, what is the Dx?
BOTH infective arthrits and gouty arthritis.
