Cellulitis

Key Differential
Diagnoses

Necrotising fasciitis
Osteomyelitis
DVT

Key Investigations

Wound swab
FBC, ESR, CRP
U+E, LFT, Bone, Glucose
BC

Key Treatment

PO FLUCLOXACILLIN 500 mg-1 g qds; mild, outpatient
IV FLUCLOXACILLIN 2 g qds  (+ IV GENTAMICIN 5 mg/kg od + PO RIFAMPICIN 600 mg bd OR IV CLINDAMYCIN 600 mg qds); severe, inpatient

Key Management
Decisions

Admit?
MRI (osteomyelitis or necrotizing fasciitis)
Surgery (necrotizing fasciitis)

Definition

Deep infection of connective tissue, usually skin and subcutaneous tissues, in which there is obvious oedema. Erysipelas is a form of cellulitis      

• The orbital region can also be affected by cellulitis. This can be caused by an external focus of infection (eg a wound); or an infection that extends from the nasal sinuses or teeth, or metastatic spread from infection elsewhere
• Symptoms include eyelid pain, discoloration, and swelling; also causes fever, malaise, proptosis, impaired ocular movement, and impaired vision
• Diagnosis is based on history, examination, and CT or MRI. Treatment is with antibiotics and sometimes surgical drainage

Epidemiology

Little is known
No predilection for one sex or race 

Sites

One limb (usually)
Two limbs (occasionally, depends on cause)    
Non limb tissues (eg face)

Causes
(common organisms)

• Gp A, β-haemolytic streptococci (eg Streptococcus pyogenes)
• Staphylococcus aureus; typically more localised, and usually occurring with an open wound or cutaneous abscess

• Methicillin-resistant S. aureus (MRSA) has become more common in the community. Historically, MRSA was typically confined to patients who were exposed to the organism in a hospital or nursing facility. MRSA infection should now be considered in patients with community-acquired cellulitis, particularly in those with cellulitis that is recurrent or unresponsive to monotherapy. Also:
• Gp B streptococci: eg S. agalactiae; especailly in older patients with diabetes
• Gram-negative bacilli: eg Haemophilus influenzae in children; and Pseudomonas aeruginosa in patients with diabetes or neutropenia, hot tub or spa users, and hospitalised patients
• Pasteurella multocida: bites from from cats; and Capnocytophaga sp (dogs)
• Aeromonas hydrophila (fresh water)
• Vibrio vulnificus (warm salt water)
• Fungi

Risk factors

Identifiable break in skin, usually from:
Trauma (eg laceration, burn, or bite)
Or ulceration (eg leg)
Or concomitant skin disorder (atopic eczema, fungal infections eg tinea pedis)
Note: cellulitis that has spread from an adjacent structure (eg osteomyelitis) or through the blood (bacteraemia) is very serious and requires immediate treatment with IV antibiotics
Obesity, immunosuppression, PVD
Note: cellulitis can occur in a patient with no DM; and frequently no obvious risk factors, or skin break

Symptoms

Acute onset of red, hot, painful rash
Signs systemic infection (fever, malaise, acute confusion, nausea and rigors)
Note: these symptoms may precede the skin changes (sometimes by several hours)
Enlarged nodes (lymphangitis) of same limb

Key questions

"When did the rash start?"    
"Have you been bitten or burnt recently?"        

Signs

Fever
Red, hot, painful, rash, with oedema and tender skin; can have appearance of skin of an orange ('peau d'orange')
± petechiae (common), vesicle or bullae formation (can rupture); sometimes with necrosis of involved skin
Enlarged nodes (lymphangitis) same limb

Blood

FBC (WC usually raised), CRP, ESR
U+E, LFT, Bone, Glucose
BC            

Other

CXR, if diagnostic confusion
Wound swab if visible portal of entry for bacteria (eg open wound)
Mark extent of rash with marker pen, as baseline

Specialist investigation

MRI (if considering osteomyelitis or necrotizing fasciitis)

Differential diagnosis

3 most important differential diagnoses:
1. Necrotizing fasciitis; look for crepitus, severe pain (inappropriate for extent of rash), sensation loss; needs urgent surgery; frozen biopsy and/or MRI, if will not delay diagnosis or Rx; [Ref]
2. Osteomyelitis; think about diagnosis in patient with DM and foot ulcers
[Ref]
Note: a normal XR does not exclude osteomyelitis; you need a NM bone scan and/or MRI
3. Deep venous thrombosis (do they have any risk factors? See table below)

Other: infected eczema/psoriasis, ruptured Baker's Cyst, varicose eczema (but usually bilateral with crusting, scaling, and itch); rarely gangrene, acute gout, adverse drug reactions, metastatic cancer (carcinoma erysipeloides)

Feature

Lymphangitis
+ regional
lymphadenopathy

Treatment
(first line)

Drugs 
PO FLUCLOXACILLIN 500 mg-1 g qds (mild, outpatient); Penicillin Allergy: PO DOXYCYCLINE 200 mg od OR PO ERYTHROMYCIN 500 mg qds
IV CEFTRIAXONE 2 g od (moderate, outpatient); see 'Risk Stratification ' below
IV FLUCLOXACILLIN 2 g qds iv (± IV GENTAMICIN 5 mg/kg od + PO RIFAMPICIN 600 mg bd OR IV CLINDAMYCIN 600mg qds; severe, inpatient); Penicilin Allergy: IV VANCOMYCIN 1 g bd ± (IV GENTAMICIN 5 mg/kg od + PO RIFAMPICIN 600 mg bd)
IV line (+fluids, if dry)

Stop

?Immunosuppression (after DW prescriber)

Treatment
(second line)

Drugs:
Consider adding another antibiotic, if cellulitis has arisen from a wound contaminated with water:
PO DOXYCYCLINE (100 mg od) for saltwater contamination
PO CIPROFLOXACIN (750 mg bd) for freshwater contamination
± GCSF in patients with DM

Procedures:
Elevate leg
(If unwell) urinary catheter, CVP line, arterial line

Admit?

Usually, especially if:
• Severe or rapidly deteriorating cellulitis (eg affecting extensive areas of skin or which is spreading), or an uncertain diagnosis with sinister signs or symptoms (eg possible necrotizing fasciitis)
• Comorbidities that complicate or delay healing (eg PVD, chronic venous insufficiency, morbid obesity, immunosuppression, IV drug use)
• Other factors: frail, elderly; facial cellulitis; periorbital cellulitis (+refer to ophthalmologist); failure to respond to oral antibiotics; recurrent cellulitis

Bed plan

Medical admission ward
± ITU
± Dermatology

Referrals

General surgery ASAP, if suspect necrotising fasciitis
Orthopaedics, if suspect osteomyelitis
Dermatology, if not improving in 24h
Microbiology, if not improving in 24h

Complications

• Severe sepsis/shock
• Local abscesses may require incision and drainage
• Recurrences in the same area are common; sometimes leading to lymphatic damage, chronic lymphatic damage and lymphoedema
• Rarely, can lead to necrotizing subcutaneous infection, requiring rapid surgical intervention
• Also rarely, bacteraemia with metastatic foci of infection (disciitis, endocarditis)

Follow-up

GP (7 days AB); if no substantial improvement, assess compliance, and continue Rx for further 7 days
If swabs were taken, use sensitivity results to guide Rx
Dermatology (re) referral, if extended treatment is ineffective

Risk stratification: who can be managed as an outpatient

[Ref]

2° Prevention  
+ Health promotion 

(If obese) lose weight
(If diabetic) look at feet every day, and seek help if any small lesion develops
Treat tinea pedis (risk factor)

Don't forget

Patients can (and do) die of cellulitis

Red flags

• Reduced conscious level, confusion
• Speed of rash spreading
• Severe sepsis/shock
• Excessive pain (think alternative diagnoses eg necrotising fasciitis)