Infections

Question 1

What is cellulitis?

Answer 1

Acute, non-purulent spreading infection of the subcutaneous tissue and dermis, causing overlying skin inflammation.

Question 2

What is erysipelas?

Answer 2

A form of superficial cellulitis involving the upper dermis and superficial lymphatics

Question 3

What is the aetiology of cellulitis and erysipelas? (x4)

Answer 3

• Penetrating injury e.g., cannulation
• Local lesions such as insect bites
• Fissuring such as anal fissures
• Rarely, can arise spontaneously from blood-borne sources

Question 4

What are the common causative organisms in cellulitis and erysipelas? (x2)

Answer 4

Streptococcus pyogenes and Staphylococcus aureus.

Question 5

What are the risk factors in cellulitis and erysipelas? (x3)

Answer 5

Poor hygiene and poor vascularisation of tissue (e.g., diabetes mellitus, peripheral vascular disease). Toe-web abnormalities as this may lead to a fissure and subsequent site of entry for pathogens.

Question 6

What is the epidemiology of cellulitis and erysipelas?

Answer 6

Very common.

Question 7

What are the signs and symptoms of cellulitis? (x3) Where?

Answer 7

• Erythema, oedema, warm and tender with acute onset and rapidly spreading. It can be well-demarcated or have indistinct margins.
• Typically found on limbs.
• Vesicles, blisters and petechiae when severe
• Pyrexia due to systemic spread

Question 8

What are the signs and symptoms of periorbital cellulitis?

Answer 8

Swollen eyelids and erythematous skin changes.

Question 9

What are the signs and symptoms of orbital cellulitis?

Answer 9

Painful eye movements, visual impairment, exophthalmos.

Question 10

What are the signs and symptoms of erysipelas? (x5) Where?

Answer 10

• Raised, WELL-DEFINED, tender, BRIGHT RED rash with acute onset and rapidly spreading
• Typically found on face as well as limbs
• Vesicles, blisters and petechiae when severe
• Peau d’orange caused by superficial oedema around hair follicles which remain attached to the dermis
• Pyrexia due to systemic spread
• Lymphadenopathy and lymphangitis (infection spreading up through lymphatic vessels)

Question 11

What are the investigations for cellulitis and erysipelas?

Answer 11

• BLOOD: WCC is always high or low (if it is normal, it is probably not cellulitis or erysipelas), ESR/CRP raised. Take blood culture if systemically unwell
• SKIN SWAB: antibiotic sensitivity if systemically unwell
• SKIN ASPIRATION: antibiotic sensitivity if systemically unwell and there is a collection of fluid

Question 12

How is cellulitis and erysipelas managed?

Answer 12

EMPIRICAL ANTIBIOTICS: flucloxacillin (oral in non-severe, IV if severe), then clarithromycin or doxycycline. Add vancomycin if suspected MRSA. If in face triangle, first-line is amoxicillin/clavulanate

Question 13

What is meant by treating empirically?

Answer 13

Treating with best guess i.e. without knowing causative organism definitively.

Question 14

What are the complications of cellulitis and erysipelas? (x6)

Answer 14

• Sepsis
• Chronic oedema in affected area where cellulitis or erysipelas has damaged lymphatic drainage
• Necrotising fasciitis – penetrates deeper
• Sloughing of overlying skin
• Meningitis (if in danger triangle)
• Cavernous sinus thrombosis (if in danger triangle)

Question 15

What is cutaenous candidiasis?

Answer 15

Overgrowth of Candida resulting in red, itchy rash following penetration below surface of skin.

Question 16

What is the aetiology of cutaneous candidiasis? (x2)

Answer 16

Candida naturally lives on skin, so infection occurs when the fungus penetrates the skin. This is common in areas where the skin is moist or warm (creases, axilla, groin). Immunocompromised individuals are also more susceptible.

Question 17

What are the signs and symptoms of cutaneous candidiasis?

Answer 17

Red, itchy rash in folds of skin, causing the skin to become cracked and sore. Blisters and pustules may also occur.

Question 18

What is molluscum contagiosum?

Answer 18

Cutaneous skin lesions caused by Molluscum contagiosum. Molluscum contagiosum is a pox virus (double stranded DNA)

Question 19

What is the aetiology of molluscum contagiosum? (x3)

Answer 19

• MCV 1: seen in children and as a result of child-to-child skin contact or fomites
• MCV 2: sexually transmitted in adults
• MCV 3: rare subtype in any age group

Question 20

What is the pathophysiology of molluscum contagiosum?

Answer 20

Virus infects keratinocytes (epidermal layer) and mucosa causing papular lesions. The virus induces abnormal keratinocyte growth. The epidermal collections of abnormal keratinocytes are called Henderson-Patterson bodies (microscopy). Despite the abnormal cellular growth, MCV does not cause dysplasia.

Question 21

What is the disease course of molluscum contagiosum?

Answer 21

2-4 years in immunocompetent individuals.

Question 22

What is the epidemiology of molluscum contagiosum: Age? Climate?

Answer 22

Highest incidence in children. Higher in tropical climates.

Question 23

What are the signs and symptoms of molluscum contagiosum? (x4)

Answer 23

• LESIONS: appear as umbilicated (central depressions), pearl-like, smooth papules. Distribution is typically over chest and axilla in children, and groin in adults.
• Local erythema and swelling – called inflamed molluscum and typically a marker of immune response to the lesion
• Pruritus
• Coexistent atopic eczema

Question 24

What are the investigations for molluscum contagiosum? (x2)

Answer 24

• CURETTAGE BIOPSY (ring-like blade to biopsy lesion): in diagnostic uncertainty
• HAEMATOXYLIN AND EOSIN STAINING: Henderson-Patterson bodies stain heavily