Cellulitis

Table of contents
Key points ⚡
Succinct notes to superpower your revision
Cellulitis\: Bacterial skin infection, a
Erysipelas\: More super
Causative organisms\: S t r e p t o c o c c u s p y o g e n e s , S t a p h y l o c o c c u s a u r e u s ; children/immunocompromised patients at risk
from S t r e p p n e u m o n i a e , H . i n
Risk factors\: Trauma, ulcers, skin barrier dysfunction (eczema, psoriasis), peripheral oedema, peripheral venous disease,
peripheral neuropathy, immunosuppression (diabetes, neutropenia, immunosuppressant medication).
Symptoms\: Erythema, tender skin, warmth, swelling, fevers, typically unilateral, often in lower limbs.
Clinical signs\: Erythematous rash (di
Eron classi
comorbidities), Class 3 (SIRS/very poorly controlled comorbidities), Class 4 (septic shock/life-threatening infection).
Di
lipodermatosclerosis (tender/red, usually bilateral), septic arthritis (overlying joints, reduced ROM), vasculitis (non-
blanching rash), thrombophlebitis (linear tracking), compartment syndrome (swollen, tense, pain).
Investigations\: Basic observations, wound swab, FBC (raised WCC), U&Es, CRP, blood cultures, VBG (pH, lactate),
ultrasound (exclude abscess/DVT), X-ray/MRI (osteomyelitis).
Management\: Outline erythema, encourage
safety net advice. Antibiotics\: oral (
requiring IV antibiotics.
Complications\: Sepsis, abscess, recurrence, ulceration, post-streptococcal nephritis, osteomyelitis, compartment
syndrome, necrotising fasciitis (rapidly progressive, crepitus, disproportional pain, necrotic lesions, treated with surgical
debridement and IV antibiotics).
Article 🔍
A comprehensive topic overview

Introduction

Cellulitis and erysipelas are common bacterial infections of the skin. It a
a

Aetiology

Skin anatomyCellulitis a
superFigure 1. The layers and structures of the skin.
Causative organisms
Common causative organisms include S t r e p t o c o c c u s p y o g e n e s and S t a p h y l o c o c c u s a u r e u s .
Children or immunocompromised patients, such as those with diabetes, are at risk of infections caused by S t r e p
p n e u m o n i a e , H .i n
necrotising fasciitis after surgery (commonly known as gas gangrene).

Risk factors

Risk factors for cellulitis include\:
Trauma\: bites, scratches or burns
Ulcers
Skin barrier dysfunction\: conditions such as eczema or psoriasis
Peripheral oedema
Peripheral venous disease
Peripheral neuropathy
Immunosuppression\: diabetes, neutropenia or immunosuppressant medication

Clinical features

Cellulitis is usually unilateral and most commonly a
History
Typical symptoms of cellulitis include\:
Erythema
Tender skin
Warmth
Swelling
Fevers
Other important areas to cover in the history include\:
Recent trauma to the skin
Past medical and drug history\: immunosuppression
Clinical examination
Typical clinical signs of cellulitis include\:
Erythematous rash\: the border may be di
Hot and tender to touch
Oedematous
BlistersUlcers
Figure 2. Cellulitis of the left leg
Eron classi
Class 1\: Systemically well with no co-morbidities
Class 2\: Systemically unwell or well with poorly controlled co-morbidities
Class 3\: Large SIRS response or very poorly controlled co-morbidities
Class 4\: Septic shock or life-threatening infection

Di

Cellulitis usually presents with a unilateral red and swollen limb, which can be di
such as deep thrombosis (DVT).
Di
Deep vein thrombosis (DVT)\: unilateral presentation similar to cellulitis but without systemic upset; check for risk factors
and use Well’s score to aid diagnosis.
Venous insu
Lipodermatosclerosis\: can be tender and bright red; no systemic features are present. Usually bilateral.
Septic arthritis\: if erythema is overlying joints and reduced range of movement
Vasculitis\: non-blanching rash with palpable petechial/purpuric presentation
Thrombophlebitis\: linear tracking along the path of the a
Compartment syndrome\: swollen, tense and pain to light touch
Bilateral lower limb cellulitis
Bilateral cellulitis is incredibly rare. Patients with bilateral lower limb erythema and swelling are far more likely to
have venous insu

Investigations

Bedside investigationsRelevant bedside investigations may include\:Basic observations (vital signs)\: to ensure haemodynamic stability
Wound swab
Laboratory investigations
Relevant laboratory investigations may include\:
Full blood count\: raised white cells indicate in
Urea and electrolytes\: as a baseline, renal function may be impaired due to infection
CRP\: raised with in
Blood cultures
Venous blood gas\: to assess pH and lactate
Imaging
Most cases of cellulitis are managed without imaging. However, an ultrasound of the a
exclude an underlying abscess or deep vein thrombosis (DVT).
X-ray or MRI can be used to investigate for underlying osteomyelitis. X-ray changes can lag behind disease progression.
Therefore, de

Management

Most cases of cellulitis are managed in the community; however, it is important to be aware of reasons to arrange hospital
admission. These may include\:
Signs of haemodynamic instability
Rapidly worsening cellulitis
Facial or orbital cellulitis
Extremes of age
Immunocompromised individuals
Patients should always be managed according to how they present clinically. Patients with cellulitis can be acutely unwell
and always consider the possibility of sepsis.
Supportive management
All areas of erythema should be outlined to monitor its spread.
Encourage patients to drink plenty of
and temperatures.
Patients who are suitable for outpatient management should be reviewed after 48 hours to ensure they respond to oral
treatment. If they are not responding, referral to secondary care should occur.
Patients should be safety-netted with advice to seek medical attention if they become systemically unwell, spreading
erythema or if they are unable to take their antibiotics.
Medical management
Antibiotics should be prescribed according to severity and allergy status. Flucloxacillin or doxycycline (for those with a
penicillin allergy) for 5 - 7 days are standard
Intravenous antibiotics should be used for severe infections (Eron class 3 or 4) or those that do not respond to oral options.
Outpatient parenteral antimicrobial therapy (OPAT) may be considered for those who require IV antibiotics but are clinically
stable (Class 2).
IV
ProphylaxisSpecialists may consider prophylactic antibiotics if there have been two separate episodes of cellulitis within the
last 12 months. The

Complications

Complications of cellulitis include\:
Sepsis
Abscess formation
Recurrence of infection
Ulceration
Post-streptococcal nephritis
Osteomyelitis
Compartment syndrome
Necrotising fasciitis
Necrotising fasciitis
Necrotising fasciitis is a severe complication of cellulitis which needs to be excluded.
It typically presents with rapidly progressive erythema, crepitus, disproportional pain to stimuli and necrotic lesions.
The mainstay of treatment is urgent surgical debridement and IV antibiotics.

References

NICE CKS. Cellulitis. Published in 2023. Available from\: [LINK]
Patient UK. Cellulitis and Erysipelas. Published in 2020. Available from\: [LINK]
Diagnosis and management of cellulitis. Published in 2018. Available from\: [LINK]
Santer, M et al. Management of cellulitis\: current practice and research questions. Published in 2018. Available from\: [LINK]
DermNet. Cellulitis mimics. Published in 2018. Available from\: [LINK]
Image references
Figure 1. Wong, D.J. and Chang, H.Y.Anatomy of the skin. License\: [CC BY]
Figure 2. Campbell. Cellulitis left leg. Licence\: [Public domain]

Reviewer

Dr Ehi Okpe
Consultant in Acute Internal Medicine

Related notes

Acne vulgaris
Basal Cell Carcinoma (BCC)
Cutaneous Squamous Cell Carcinoma (SCC)Erythema Multiforme
Erythema Nodosum

Test yourself

Contents

Introduction
Aetiology
Risk factors
Clinical features
Source\: geekymedics.com