Cellulitis

Question 1

Cellulitis is an acute … infection of the skin.

Answer 1

Cellulitis is an acute bacterial infection of the skin.

Question 2

Cellulitis refers to an acute bacterial skin infection that affects both the … and … tissue. It may occur anywhere on the body and ranges form a self-limiting infection to severe … infection.

Answer 2

Cellulitis refers to an acute bacterial skin infection that affects both the dermis and subcutaneous tissue. It may occur anywhere on the body and ranges form a self-limiting infection to severe necrotising infection.

Question 3

Cellulitis is a very common condition. It can occur at any age, but is mostly seen in middle-aged to older adults and usually affects the … limbs.

Answer 3

Cellulitis is a very common condition. It can occur at any age, but is mostly seen in middle-aged to older adults and usually affects the lower limbs.

Question 4

Cellulitis is commonly caused by both … and … species.

Answer 4

Cellulitis is commonly caused by both Streptococcus and Staphylococcus species.

Question 5

Cellulitis occurs due to disruption of the skin barrier (e.g. cut, abrasion), which allows entry of microorganisms. Both … and Staphylococcus are common skin commensal organisms that can enter the skin and cause infection.

Answer 5

Cellulitis occurs due to disruption of the skin barrier (e.g. cut, abrasion), which allows entry of microorganisms. Both Streptococcus and Staphylococcus are common skin commensal organisms that can enter the skin and cause infection.

Question 6

Risk factors for cellulitis: (7)

Answer 6

Trauma
Leg ulceration
Fungal infection
Lymphoedema
Venous insufficiency
Obesity
Pregnancy

Question 7

… is characterised by the hallmarks of inflammation including pain, swelling, warmth and erythema.

Answer 7

Cellulitis is characterised by the hallmarks of inflammation including pain, swelling, warmth and erythema.

Question 8

Symptoms of cellulitis (5)

Answer 8

Pain
Redness
Swelling
Fever
Malaise

Question 9

Signs of cellulitis:

Answer 9

Pain on palpation
Erythema
Skin warmth
Superficial bullae or blisters: may be present
Abscess: may complicate cellulitis. Collection of pus within dermis or subcutaneous space. Painful and fluctuant.
Lymphadenopathy

Question 10

Cellulitis is a clinical diagnosis based on the classic appearance of …, warm and … skin.

Answer 10

Cellulitis is a clinical diagnosis based on the classic appearance of erythematous, warm and oedematous skin.

Question 11

Are investigations needed for cellulitis?

Answer 11

Laboratory investigations are often unnecessary if the patient is otherwise clinically well. They are more likely to be completed in patients presenting to secondary care (e.g. hospital)

Question 12

Erysipelas - This describes a form of … that involves the more superficial dermal structures. It is characterised by a raised, well demarcated border and usually occurs secondary to beta-haemolytic streptococcal infection. Treatment is also with antibiotics.

Answer 12

This describes a form of cellulitis that involves the more superficial dermal structures. It is characterised by a raised, well demarcated border and usually occurs secondary to beta-haemolytic streptococcal infection. Treatment is also with antibiotics.

Question 13

The severity of cellulitis may be assessed using the … classification:

Answer 13

Class I: no signs of systemic toxicity. No uncontrolled co-morbidity (e.g. diabetes mellitus)
Class II: systemically unwell or systemically well but with a comorbidity
Class III: significant systemic upset (e.g. tachycardia, tachypnoea), unstable co-morbidities or limb-threatening infection due to vascular compromise.
Class IV: sepsis or severe life-threatening infection (e.g. development of necrotizing fasciitis)

Question 14

Differential diagnosis for cellulitis: Several infective and non-infective aetiologies may be confused with cellulitis.
List the infective differentials (5)

Answer 14

Necrotising fasciitis: a severe skin infection that causes progressive destruction of the muscle fascia and overlying subcutaneous fat. It is a surgical emergency requiring urgent debridement.
Toxic shock syndrome: invasive group A streptococcal infection that may cause necrotising soft tissue infection. Due to the release of exotoxins that act as ‘superantigens’ and large release inflammatory cytokines.
Septic arthritis: joint infection. May be difficult to distinguish if cellulitis overlies a joint
Bursitis: inflammation of a bursa (fluid-filled sac). May present alongside cellulitis
Osteomyelitis: may be present with overlying cellulitis.

Question 15

Differential diagnosis for cellulitis: Several infective and non-infective aetiologies may be confused with cellulitis.
List the non-infective differentials (6)

Answer 15

Deep vein thrombosis: can also cause a painful, swollen, erythematous leg
Contact dermatitis: characteristically pruritic and no systemic signs of infection
Drug reaction: usually distinguished by typical location (trunk, proximal extremities) and erythematous maculopapular rash
Insect bite: may trigger local inflammatory reaction at punctured site. Alternatively, may be delayed skin reaction with features of local swelling, itching and erythema.
Lymphoedema: abnormal accumulation of interstitial fluid
Stasis dermatitis: inflammatory reaction due to chronic venous insufficiency

Question 16

Bedside investigations for a patient with cellulitis who is systemically unwell, at risk of deterioration, or suspected of having complications

Answer 16

Skin swabs: debrided material, open wound, obvious portal for bacterial entry
Blood glucose: patients with diabetes at increased risk

Question 17

Bloods for a systemically unwell patient with cellulitis include:

Answer 17

FBC
U&E
LFT
CRP
Blood cultures: < 10% of blood cultures are positive in cellulitis
HbA1c

Question 18

Imaging for a systemically unwell patient with cellulitis:

Answer 18

Ultrasound: may be used to look for underlying abscess

X-ray: may be needed to assess for osteomyelitis

Question 19

Management of cellulitis:

Answer 19

The principle management of cellulitis is with antibiotics

Question 20

Patients with mild cellulitis (e.g. Eron I and some Eron II) - how are they treated?

Answer 20

Patients with mild cellulitis (e.g. Eron I and some Eron II) may be treated in the community with oral antibiotics. Typical antibiotic choices are penicillin (e.g. phenoxymethylpenicillin) and/or flucloxacillin due to the high rate of streptococcal and staphylococcal infections. Erythromycin/clarithromycin are good alternatives in patients with penicillin allergy (local antibiotics guidelines should always be sought).

Question 21

What are the typical antibiotic choices for mild cellulitis? (Eron I and some Eron II)

Answer 21

Typical antibiotic choices are penicillin (e.g. phenoxymethylpenicillin) and/or flucloxacillin due to the high rate of streptococcal and staphylococcal infections.

Question 22

What are the typical antibiotic choices for mild cellulitis in patients with a penicillin allergy? (Eron I and some Eron II)

Answer 22

Erythromycin/clarithromycin are good alternatives in patients with penicillin allergy (local antibiotics guidelines should always be sought).

Question 23

Some patients with cellulitis may require hospital admission for assessment and intravenous antibiotics. These include patients with:

Answer 23

Eron class III or IV
Severe, rapidly developing cellulitis
High-risk patient: very young (e.g. < 12 months old), frail, immunocompromised
Orbital/facial cellulitis: high risk of complications
Significant lymphedema (unlikely to resolve with oral antibiotics)
Suspected complications: e.g. septic arthritis or osteomyelitis

Question 24

IV antibiotic options for cellulitis:

Answer 24

Intravenous flucloxacillin, clindamycin and/or vancomycin may be used as intravenous antibiotic choices. Clindamycin is particularly important in patients with suspected group A streptococcal infection as it suppresses bacterial exotoxin production (plus other beneficial effects). Clindamycin may be needed in combination with a beta-lactam antibiotic (e.g. penicillin, cephalosporin, carbapenem).

In patients with severe cellulitis or systemically unwell, advice from microbiology is usually required. It is always recommended to follow local antibiotic guidelines.

Question 25

Cellulitis may cause life-threatening … or … infections (e.g. … …).

Answer 25

Cellulitis may cause life-threatening sepsis or necrotising infections (e.g. necrotising fasciitis).

Question 26

Acute complications of cellulitis:

Answer 26

Necrotising infections (e.g. necrotising fasciitis)
Sepsis
Abscess: may require incision and drainage
Myositis: infection of muscle

Question 27

Chronic complications of cellulitis:

Answer 27

Persistent leg ulceration
Recurrent cellulitis
Lymphoedema: damage to lymphatic system

Question 28

What is this showing?

Answer 28

Cellulitis

Question 29

Which of the following clinical features is not one of the hallmarks of inflammation?
Erythema
Pain
Swelling
Warmth
Lymphadenopathy

Answer 29

The hallmarks of inflammation include pain, swelling, warmth and erythema.

These hallmarks were traditionally referred to as rubor (redness), calor (increased heat), tumor (swelling) and dolor (pain). They were first described in 1 AD by the Roman scholar Aulus Cornelius Celsus. A fifth component, loss of function, was added to these hallmarks in the 19th century by German pathologist Rudolf Virchow.

Lymphadenopathy may occur in inflammation due to recruitment of inflammatory cells. However, it is not one of the ‘hallmarks’ of inflammation.

Question 30

Which of the following sites of cellulitis is most concerning due to the high risk of complications?

Calf
Hand
Foot
Groin
Orbit

Answer 30

Orbital cellulitis refers to an infectious process involving the muscles and fat of the orbit that lie deep to the orbital septum.

Question 31

Cellulitis involving the orbital structures can be divided into pre-septal and orbital cellulitis

Answer 31

• Pre-septal: inflammation/infection of the superficial layers anterior/superior to the orbital septum
• Orbital: inflammation/infection of the muscles and fat of the orbit posterior/deep to the orbital septum

Question 32

What is the primary site of infection in Erysipelas?

Answer 32

Erysipelas refers to a superficial form of cellulitis that predominantly affects the upper dermis.

Question 33

A 72 year old female presents to the GP with a hot, swollen left lower limb. She was gardening over the weekend and acquired a few scratches over the lower part of the left leg. In the last 24 hours, the redness has spread and she feels generally unwell with fever and nausea. On examination, there is marked inflammation of the entire left calf, which is mildly tender but she is still able to move it without difficulty. Observations are taken in the practice that show HR 115 bpm, BP 140/95, RR 22, saturations 99% room air, temperature 37.8º. She has a background of diabetes mellitus on metformin, hypertension on ramipril and osteoarthritis.

What is the most appropriate management in this case?

Answer 33

The rapid progression in symptoms, significant co-morbidities and systemic upset (fever, tachycardia, tachypnoea) means urgent hospital admission is warranted.

This patient should be admitted to hospital for urgent assessment, blood tests and intravenous antibiotics. This represents an Eron III cellulitis and given her age, history of diabetes mellitus and rapid onset necrotising fasciitis should be considered. Necrotising fasciitis is a severe skin infection that causes progressive destruction of the muscle fascia and overlying subcutaneous fat. It is a surgical emergency requiring urgent debridement.