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MBBS II MSS > L07 - Infections of the skin, soft tissues, bones, and joint > Flashcards

L07 - Infections of the skin, soft tissues, bones, and joint Flashcards

1
Q

4 crude layers of the skin?

A

Epidermis
Dermis
Subcutaneous tissue
Deep fascia

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2
Q

What are the more common infection sites out of skin, bone, joint and soft tissues?

A

Skin and soft tissue infection are most common

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3
Q

List 4 defense mechanisms of the skin?

A 
■ 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
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4
Q

What type of bacteria make up majority of normal skin flora?

A

Mostly gram +ve

Most abundant = Staphylococcus (primarily coagulase-negative staphylococci i.e Staph. epidermidis)

Corynebacterium spp.

Propionibacterium acnes

Micrococcus spp.

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5
Q

What are other less common skin flora organisms?

A

Gram-negative bacilli (e.g. Acinetobacter, Pseudomonas, other non-fermenters) @elderly, hospitalized

Yeasts (e.g. Candida, Malassezia furfur) @ moist area of body

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6
Q

What factors can influence the make up of skin flora?

A 
– Age 
– Body location 
– Occupation 
– Hospitalization 
– Medications 
– Diseases (local and systemic)
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7
Q

What are the 4 pathways in the pathogenesis of skin infections?

A
  1. Breach of normal integrity of skin (e.g. trauma / abrasions, iatrogenic (surgery, intravenous catheter))
  2. Alteration of normal skin flora
  3. Changes in local environment of tissues, e.g. Presence of devitalized tissues; in surgical wounds: haematoma, foreign bodies, etc.
  4. Introduction of pathogenic exogenous (e.g. Vibrio from seawater; dog bites) / endogenous microbial flora
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8
Q

What is the name of ringworm infection?

A

Dermatophytosis

caused by fungi, named based on appearance, no worms involved.

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9
Q

Define dermatophytosis?

A

Infection of keratinized tissues by keratinolytic dermatophytic fungi / mould

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10
Q

List 3 organisms that can cause dermatophytosis?

A

All 3 are moulds

Trichophyton spp.

Microsporum spp.

Epidermophyton floccosum

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11
Q

Difference between dermatophytosis and dermatomycoses?

A

Dermatophytosis = infection by keratinolytic dermatophytic fungi

Dermatomycoses = infection by non-dermatophytic fungi

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12
Q

How do dermatophytic moulds survive on skin?

A

feed on keratin of skin, hair, skin appendages to obtain nutrients

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13
Q

Explain the diagnostic tests for dermatophytosis?

A

1) KOH wet mount (dissolves keratin to expose fungus. Hyaline fungal strands can be seen)
2) Fungal culture (long time)

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14
Q

What is the clinical presentation of dermatophytosis?

A

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

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15
Q

Causative pathogen and clinical presentation of impetigo?

A

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

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16
Q

What is the morphology and location of Carbuncles?

A

large, contiguous groups of furuncles

Commonly at the back / trunk region

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17
Q

What is the epidemiology of carbuncles?

A

Mainly affect:

 Elderly, hospitalized
 Diabetic
 Immunocompromised patients (e.g. Pseudomonas aeruginosa)

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18
Q

What is the morphology of Furuncle?

A

Furuncles = boils

  • Painful, deep subcutaneous abscess around hair follicle
  • Rupture of skin can release pus inside
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19
Q

What is infected in Cellulitis? What are the causative pathogens?

A

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.

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20
Q

Clinical presentation of cellulitis?

A

1) Local region of inflammation (redness, swelling) with ill-defined margin
2) ± local abscess
3) Fever, chills, bacteraemia

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21
Q

What are common types of Pyoderma?

A

Impetigo

Folliculitis

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22
Q

What is the pathology and causative pathogen of Erysipelas?

A

Form of cellulitis but is not cellulitis

mostly caused by beta-haemolytic streptococci/ Group A Strep.

Marked subepidermal oedema with Heavy infiltration of neutrophils

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23
Q

Clinical presentation of Erysipelas?

A

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

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24
Q

What is Paronychia and what causes it?

A

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)

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25
Q

Clinical presentation of Paronychia?

A

Rapid onset of erythema, edema, and tenderness at proximal nail folds

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26
Q

What is the most urgent form of cellulitis?

A

Peri-orbital cellulitis

Around eyelids, possible intra-orbital or intra-ocular involvement

Need aggressive therapy

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27
Q

What is the treatment for MSSA infections?

A

Methicillin-sensitive Staphylococcus aureus

Use:
1) Cloxacillin (penicillin, β-lactamase-resistant);

2) Augmentin
3) 1st generation cephalosporins (cefadroxil, cefalexin)

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28
Q

What are the 2 types of MRSA?

A

Hospital-acquired MRSA (HA-MRSA)

Community-associated MRSA (CA-MRSA)

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29
Q

What is the typical presentation of CA-MRSA?

A

soft tissue abscess formation (e.g. furuncles, carbuncles)

Occasionally present as necrotizing pneumonia (fulminant, rapidly fatal) in young individuals

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30
Q

What are the unique features of CA- MRSA compared to HA-MRSA?

A

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

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31
Q

What type of infection involves Dermis, subcutaneous fat, deep fascia, muscle?

A

necrotizing soft tissue infections

32
Q

Name 2 forms of necrotizing soft tissue infection?

A

Clostridial myonecrosis (gas gangrene)

Necrotizing fasciitis (most common)

33
Q

Types of necrotizing fasciitis and their causative agents?

A

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.)

34
Q

Type I necrotizing fasciitis occurs in which patients?

A
  • After intra-abdominal/ pelvic surgery

- Arise de novo in perineal area&raquo_space; Fournier’s gangrene @ scrotum of elderly

35
Q

Type III necrotizing fasciitis occurs after what exposure?

A

Exposure to contaminated water

Consumption of contaminated seafood

36
Q

Clinical presentation of necrotizing fasciitis?

A

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

37
Q

Causative agent of Clostridial myonecrosis?

A

85-90%: Clostridium perfringens

Sometimes: other Clostridium spp.

Can be mixed with facultative anaerobic bacteria (e.g. Enterobacteriaceae

38
Q

Pathogenesis of Clostridial myonecrosis?

A

muscle injury + contamination with soil / other foreign materials containing spores of Clostridium perfringens

> > coagulative necrosis of muscle fibres (infarcted, acidophilic, opaque ‘tombstone’, lost nuclei)

39
Q

Clinical presentation of Clostridial myonecrosis?

A
  • Locally, tense oedema, serosanguineous/ yellowish with small amounts of blood
  • Foul odour of the wound
  • Crepitus
40
Q

Name of infection causing abscess formation in skeletal muscle by Staphy. aureus?

A

Pyomyositis

41
Q

What muscle is common infected secondary to osteomyelitis of the spine?

A

Psoas muscle @ psoterior body wall

Psoas abscess

42
Q

How does body location of surgery affect the risk of post-op infections?

A

 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

43
Q

Clinical presentation of surgical wound infections?

A

1) Purulent drainage (pus) from the incision
2) Pain, tenderness, localized swelling, redness, dehiscence of wound
3) Fever (sometimes)

44
Q

List some bacteria expected to cause post-op infection in pelvic and abdominal surgery?

A

E. coli, Proteusspp., Klebsiella spp., etc.

Streptococci, enterococci; anaerobes.

45
Q

List some bacteria expected to cause post-op infection in Orthopaedic and neuro surgery?

A

S. aureus, coagulase-negative staphylococci

46
Q

List some bacteria expected to cause post-op infection by nosocomial infection?

A

Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia; Candida albicans

47
Q

What is the extent of involvement in osteomyelitis?

A

infectious process involving the various components of bone, viz. periosteum, medullary cavity, and cortical bone.

48
Q

3 types of osteomyelitis?

A

■ Acute osteomyelitis.
■ Chronic osteomyelitis.
■ Osteomyelitis associated with prosthetic implants

49
Q

What is the main mode of spread for osteomyelitis?

A

Haematogenous

50
Q

Pathology of Chronic osteomyelitis?

A
  1. Acute inflammation: Increased pressure in Haversian system&raquo_space; compression on / obliteration of vascular channels&raquo_space; ischaemia and bone necrosis
  2. Subperiosteal extension of infection lifts periosteum away from bone&raquo_space; new bone formation
  3. Ischaemic segments of bone separate to form the sequestrum (= piece of dead bone; hallmark of chronic osteomyelitis)
51
Q

What is the hallmark feature of chronic osteomyelitis?

A

sequestrum (= piece of dead bone)

52
Q

Causative agent for acute haematogenous osteomyelitis?

A

Generally monomicrobial infection

Commonest: Staphylococcus aureus

Streptococcus agalactiae/ pyogenes

Escherichia coli, Haemophilus influenzae

53
Q

Level of involvement in acute vertebral osteomyelitis?

A

Segmental arteries from aorta supplying vertebrae bifurcates to supply 2 adjacent bony segments

> > involves 2 adjacent vertebrae and the intervertebral disk.

54
Q

What are some predisposing factors of contiguous focus osteomyelitis?

A

– Trauma, surgical operations of bones, open fractures, chronic soft tissue infections.

– Vascular insufficiency, e.g. diabetes mellitus.

55
Q

Difference between acute haematogenous osteomyelitis and Contiguous focus osteomyelitis?

A

Acute = monomicrobial, primary infection by blood bourne pathogen

Contiguous = polymicrobial, Secondary infection from adjacent soft tissue infection

56
Q

Apart from 3 types of osteomyelitis, what is another group of bone infections?

A

Skeletal mycobacterial infection

57
Q

Types of Skeletal mycobacterial infection

and their causative agents?

A

Tuberculosis

Non-tuberculosis mycobacteria: M. marinum, M. aviumcomplex, M. fortuitum

58
Q

Clinical presentation of Contiguous focus osteomyelitis?

A

 Fever, chills
 Leukocytosis
 Pain, local swelling
 Signs, symptoms may be minimal or non-specific in some patients, e.g. infants, IV drug addicts.

59
Q

Clinical presentation of Chronic osteomyelitis?

A

 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

60
Q

Pathogenesis of Prosthesis-related osteomyelitis?

A

– Early: introduced during operation or from post-operative wound infection.

– Late: haematogenous

61
Q

What usually precedes Mycobacterium TB osteomyelitis?

A

contiguous lymphadenitis

Usually from haematogenous spread during primary infection&raquo_space; chronic osteomyelitis

62
Q

What people are typically infected by M. marinum caused osteomyelitis?

A

Typically in persons with recreational / occupational exposure to seawater

cause skin lesions / tenosynovitis (inflammation of tendon sheath)

63
Q

How to examine osteomyelitis?

A

Best option:
- Magnetic resonance imaging (MRI)

Others:

  • CT
  • Radionuclide imaging: PET
    a) Bone scan
    b) Gallium scan
64
Q

How to make Microbiological diagnosis of osteomyelitis?

A

– Blood culture.
– Biopsy of the bone lesion.
– In chronic osteomyelitis, culture of sinus tract is not reliable for predicting the organisms causing osteomyelitis.

65
Q

Treatment of osteomyelitis?

A

Antibiotic: need prolonged course

May need surgical débridement (especially chronic osteomyelitis: must remove sequestrum (dead bone))

Drain abscess

66
Q

Which part of the body is affected by Infective arthritis and why?

A

Synovium of larger joints: knee, hip, shoulder, ankle, elbow; but any joint can be involved

highly vascular, lacks basement membrane = susceptible to bacterial seeding

67
Q

Route of spread of infective arthritis?

A

 Haematogenous seeding

 Direct inoculation (e.g. open wound, percutaneous needle drainage)

68
Q

Pathogens causing Polyarthritis infective arthritis?

A
  • Viruses

- Neisseria gonorrhoeae (disseminated gonococcal infection)

69
Q

Clinical features of Infective arthritis?

A

Pain, limitation of movement at the joint

Fever, joint swelling; leukocytosis

70
Q

What autoimmune diseases can cause polyarthritis?

A

Rheumatoid arthritis, systemic lupus erythematosus, diabetes mellitus

71
Q

Common causative agents of acute bacterial arthritis?

A

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

72
Q

Clinical presentation of acute bacterial infective arthritis?

A

Usually pain, swelling, limited ROM at Larger joints

Smaller joints affected = think Neiserria gonorrheoae

Fever and Leukocytosis present

73
Q

What diseases must be differentiated from infective arthritis?

A

Rheumatoid arthritis

Crystal -induced arthritis i.e. gouty arthritis by monosodium crystal or Pseudogout by CCP crystal

Trauma, OA or tumour

74
Q

What tests can be done to differentiate infective arthritis from other causes of joint pathology?

A

■ Blood culture

■ Diagnostic synovial fluid aspirate – Leukocyte count, crystals, Gram stain, culture.

■ Synovial biopsy

75
Q

If a patient has monosodium urate crystal from synovial aspirate and positive bacteria culture, what is the Dx?

A

BOTH infective arthrits and gouty arthritis.

MBBS II MSS (31 decks)

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