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Question Bank > Skin and soft tissue infections > Flashcards

Skin and soft tissue infections Flashcards

1
Q

What is difference between erysipelas, cellulitis, necrotising fasciitis?

A

Erysipelas - superficial layers

Cellulitis - subcutaneous fat

Necrotising fasciitis - deeper layers including fascia. Often associated with severe pain

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2
Q

What are most common causes of cellulitis?

A

Staph aureus

Group A strep

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3
Q

Who should be offered antibiotic prophylaxis against cellulitis?

A

If 2 or more episodes in 12 month period

  • Phenoxymethylpenicillin
    250 mg twice a day
  • Erythromycin
    250 mg twice a day

re-assess if still required after 12 months

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4
Q

55 year old comes in drowsy, vomiting, hypotensive, pyrexial. Furuncle seen on foot, with surrounding erythema following gardening accident.

What is possible diagnosis?

A

Toxic shock syndrome

multi-organ failure mediated by bacterial toxins, which act as immunological superantigens, stimulating high levels of cytokine release - hypotension, increase tissue permeability. Desquamation occurs later.

normally antigens presented in MHC by APC. However, superantigens can bind to external MHC, and cross link with T-cell receptors. Thereofre specific MHC-TCR receptor site binding not required. So large number of T-cells are stimulated at once

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5
Q

Which organisms cause toxic shock syndrome?

A

Staph aureus - TTST-1 toxin. 3% mortality

GAS - streptococcal pyrogenic exotoxins. 30% mortality Some evidence of IVIG having benefit in streptococcal toxic shock syndrome

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6
Q

Chickenpox, complicated by cellulitis.

What is most common cause?

A

Group A strep

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7
Q

Child with rash, with fever

What are differential diagnoses?

A

Parvo B19
HHV6/7
measles
Rubella

Vesicular -
Enterovirus
VZV

Foreign travel -
chikungunya
dengue
zika

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8
Q

Child with rash, fever, conjunctivitis. What is possible diagnosis?

A

Measles

may have respiratory symptoms - cough/ coryza

may have Kopliks spots in mouth

Adenovirus

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9
Q

What is management of measles?

A

Supportive - fluids/ paracetamol

ribavirin - some evidence but not routinely used

WHO suggests vitamin A, once daily, for two days, in children who are 12 months or older

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10
Q

What are neurological complications of measles infection?

A

Acute post-infectious meningoencephalitis - occurs weeks after infection. Most recover fully

Inclusion body encephalitis - 75% die. Occurs 1 year after infection

Sub-acute sclerosing pancencephalitis - most die within 1 year. Presents within 20 years of measles infection

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11
Q

Patient with erythema migrans

What are differences in clinical picture of lyme disease acquired in UK v USA?

A

Borrelia burgdorgeri covers 15 species of bacteria which cause Lyme disease

USA - more fever, headache, fatigue. B burgdorferi sensu stricto is most common species there

UK - Borrelia afzelii, has lower virulence. Most common species in Europe

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12
Q

Apart from erythema migrans, what are other manifestations of Lyme disease?

A

meningitis
cranial nerve palsy
mononeuritis multiplex

AV block
myocarditis

arthritis

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13
Q

47 year old ma with T2DM has history of foot pain, with worsening redness.

Ulcer over plantar surface right midfoot

CRP 156
WCC 19

Wound swab from GP grew -
pseudomonas
strep agalactiae
strep equisimilis

What are other important parts of examination?

A

diabetic foot care e.g footwear, recent trauma, any metalwork

diabetic control e.g HbA1c, retinopathy

evidence of neuropathy - charcot arthropathy, claw/ hammer toes, buniones, calluses

check peripheral pulses

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14
Q

47 year old ma with T2DM has history of foot pain, with worsening redness.

Ulcer over plantar surface right midfoot

CRP 156
WCC 19

Wound swab from GP grew -
pseudomonas
strep agalactiae
strep equisimilis

What is significance of wound swab?

A

Wound swabs can be heavily contaminated, and may not indicate actual infection.

But these organisms are usual culprits -

staph aureus
streptococci
Gram neg - pseudomonas, E. coli, Klebsiella
Anaerobes

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15
Q

47 year old ma with T2DM has history of foot pain, with worsening redness.

Ulcer over plantar surface right midfoot

CRP 156
WCC 19

Wound swab from GP grew -
pseudomonas
strep agalactiae
strep equisimilis

What are next management steps?

A

X-ray/ MRI - osteomyelitis?

IV antibiotics

surgical debridement if sepsis/ life threatening infection

improved diabetic control

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16
Q

Which pathogens are associated with prosthetic joint infection?

A

Staphylococci, including CoNS

Enterococci

Diptherioids

Mycobacteria

Fungal

17
Q

Patient with cellulitis.

Staph aureus grown in pure culture.

What are important antibiotic discs to test for with regards to resistance?

A

penicillin - likely mechanism is beta-lactamase producer

cefoxitin - potent inducer of mecA gene. Predicts that organism has alteration to PBP2 - which confers pencillin resistance (MRSA)

18
Q

Patient with cellulitis.

Staph aureus grown in pure culture.

On resistance testing, you notice it is resistant to erythromycin and clindamicin.

What is significance of this?

A

if erythromycin and clindamicin discs are close together, there may be formation of a D-shaped zone of inhibition around the clindamicin.

Erythromycin can induce production of erm gene. erm gene can either be “always on”, or “inducible”. D-zone test is assessing whether inducible form is present

Bacteria closest to erythromycin re in presence of an inducer, and therefore will be resistant to clindamicin. This causes a flattening of the zone between the discs

If bacteria had erm gene always on - would have no resistnace on plate.

Can explain why some patients might fail on clindamicin

19
Q

Cat bite

Blood culture grows gram neg bacilli
oxidase pos
fail to grow on MacConkey

What is the organism?

A

Pasteurella multocida

Capnocytopahga - oxidase neg, is other option

if cat scratch (usually kitten) - then more likely to be Bartonella henselae (cat scratch disease)

infections following animal bites are often polymicrobial - one study showed average of 5 different bacteria in anima bite

serious infections more common in cat bites, than dog bites. Possibly because canines are longer and sharper than dogs

20
Q

Human bite

What are likely causative organisms?

A

Gram pos
Strep anginosus

Gram neg
Eikenella
Prevotella
Fusobacterium

21
Q

Patient has cat scratch disease

What is clinical syndrome?

A

Cat scratch - usually kitten

lesion forms 1-2 weeks later

1-2 weeks more regional lymphadenopathy develops

Caused by Bartonella henselae

difficult to diagnose - serology tests available, look for 4-fold rise in acute and convalescent serology. Biopsy is sometimes used

22
Q

Child with vesicular rash

What is differential diagnosis?

A

VZV
HSV
Enterovirus

Pox-like lesions cna look vesicular -
molluscum
monkeypox - Central/ West Africa
smallpox

23
Q

VZV can cause latent infection.

Which part of the immune system keeps in in check?

A

Cell-mediated immunity is necessary to maintain latency (not VZV antibody)

A loss of CMI, as seen in older age/ transplant/ HIV/ diabetes/ physiologic stress can lead to reactivation

24
Q

PAtient with varicella infection, admitted to hospital.

What are infection control precautions?

A

Cutaneous - skin covering and side room (until lesions are crusted)

Disseminated - respiratory and contact precautions in side room (ideally negative pressure)

Non-immune staff or pregnant should not care for patient. If non-immune person has contact, they should not have contact with other patients for 2 weeks, as may be incubating virus

The following groups are considered to be at increased risk from varicella and may require passive immunisation with Varicella Zoster Immunoglobulin (VZIG):
- pregnant women

  • neonates
  • immunocompromised individuals including those on steroids, chemotherapy
  • HIV positive
  • haematological malignancy
25
Q

What do different words mean -

varicella
varicella zoster
herpes zoster

A

varicella - chickenpox

varicella zoster - name of virus

herpes zoster - shingles

26
Q

GAS infection of skin can cause streptococcal toxic shock syndrome (STSS)

Which toxin mediates this?

A

Streptococcal pyogenic exotoxin (SpeA)

Superantigen

Binds to multitude of antigen-presenting cells/ T-cells/ Produces massive amount of proinflammatory cytokines. Activates complement, coagulation and fibronylysis cascades, which are responsible for abnormal physiological response

M1 streptococcal serotype is most common strain which has this toxin

27
Q

What is link between VZV and GAS?

A

VZV outbreaks in children cause itchy blisters which are scratched by children. They then inoculate GAS, can lead to necrotising fasciitis

This then leads to an outbreak of GAS

28
Q

GAS suspected necrotising fasciitis.

Sensitive to penicillin.

Why do we not treat with penicillin monotherapy?

A

High bacterial load means penicillin might not be able to kill all bacteria.

Established infection - bacteria might be in stationary phase. So penicillin less effect

Addition of clindamicin has been shown to reduce toxin production

29
Q

GAS.

What is D-test used for?

A

To check for clindamicin susceptibility

GAS may appear fully sensitive to clindamicin.

However. they may have an erm gene, which confers inducibile clindamicin resistance. Means that in vivo, GAS may undergo mutation to resist clindamicin

Add erythromycin near clindamicin disk. This will flatten the zone of inhibition, producing a letter D

30
Q

Slow indolent progressive skin soft tissue injection

What are possible organisms?

A 
Mycobacteria
Nocardia
Sporothrix
Histoplasma
Blastomycosis
Leishmania
31
Q

Mycobacteria which only make pigment when exposed to light, are called photochromogens.

If produce pigment independent of exposure to light, called scotochromogens

What are most common photochromogens?

A

M marinum

M kansasii

32
Q

What are symptoms/signs of RMSF?

A

rash (90%)
fever
myalgia

hyponatraemia
thrombocytopenia
increased coagulation

coagualtion issues are due to DIC which can be fatal

33
Q

What are most common species of Leishmania in:

Europe/ Africa/ Asia

South/ Central America

A

Europe/ Africa/ Asia (old world)

  • L tropica
  • L major
  • L donovani (most common cause kala-azar)

South/ Central America (new world)

  • L brasiliensis
  • L mexicana
  • L Infantum (chagasi) - visceral
34
Q

What is the immunogenic component of smallpox vaccine

A

Vaccinia virus - not Variola (smallpox)

Live vaccine (not attenuated) - produces very mild self-limiting lesion at innoculation site
Protection last approximately 5 years

Vaccinia is an orthopox virus with similar antigenic components to Variola

35
Q

What is the cause of orf

What are risk factors

A

Orf Parapox virus
Sheep/ goat farmers, vets, butcher

Parapox viruses - Orf, Milk maid’s module
Orthopox viruses - Cowpox, Monkey pox, Vaccinia, Variola

36
Q

What is the cause of Milker’s nodule

What are risk factors

A

(unspecified) Parapox virus
Dairy farmers, vets, butcher

Parapox viruses - Orf, Milk maid’s module
Orthopox viruses - Cowpox, Monkey pox, Vaccinia, Variola

37
Q

Poxviridae are classified into orthopox and parapox viruses

What are examples of each

A 
Orthopox -
Cowpox
Monkeypox
Vaccinia
Variola

Parapox -
Orf
Milk maid’s nodule

38
Q

What is difference between cowpox and milk maid nodule

A 
Cowpox -
orthopox virus
rare
more extensive distribution of lesions
usually acquired from cats/ rodents as opposed to cows
Milk maid module -
parapox virus
common
usually one lesion on hand 
usually acquired from cows
39
Q

DDx for maculopapular rash

A

Measles
Rubella

EBV
CMV
HHV6
HHV7

Parvo B19

S. Aureus
GAS

Question Bank (33 decks)

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