cellulitis is a spreading, deep skin and subcutaneous fat infection characterized by poorly demarcated erythema, swelling, warmth, and tenderness
there is often a linear proximal erythema of lymphangitis +/- tender regional lymphadenopathy
it most commonly affects the legs and is usually caused by Group A beta-haemolytic streptococcal infections
uncommonly, it may be caused by staph aureus and, in the immunocompromised, or those with unusual sources of infection by a range of microbes including Gram negatives
it tends to be rapidly progressive and may develop into severe sepsis, particularly in the immunocompromised
there are many differentials that need to be considered
failure to properly identify and treat mimickers of cellulitis can result in:
unnecessary hospital admissions
failed treatment and re-admissions
unnecessary and prolonged antibiotic Rx with risk of Cl. difficile colitis
simple, uncomplicated unilateral cellulitis of a normal adult's limb
this is in a previously well adult with no pre-existing limb pathology such as chronic oedema, and with no immunocompromise such as diabetes, corticosteroid use, etc.
there is usually an obvious cause such as a wound or perhaps entry point in foot such as cracked skin or tinea
the treating doctor should exclude/address other issues such as:
unusual infection sources - these may require different antibiotics
animal or human bites
wounds that may need debriding such as cat bites which tend to be deep puncture wounds
abscess (look for fluctuance) which will need drainage
retained foreign body - (careful history) may need xray or USS to exclude if suspected
severe sepsis - life threatening requires blood cultures and early antibiotics (broad spectrum coverage if immunocompromised), and assessment and Mx as for septic shock
necrotizing fasciitis (expanding oedematous red plaque with blue discolouration +/- blister and anaesthesia of skin) - life threatening - requires urgent theatre and broad antibiotic coverage (urgent MRI may be useful if doesn't substantially delay theatre)!
erysipelas - superficial spreading sharply defined, often shiny, red, skin infection with superficial dermal oedema due to marked dermal lymphatic involvement, +/- plaques or bullae, usually of the legs or face, caused by Strept.
impetigo or folliculitis - most likely to be Staph. aureus rather than Strept.
septic arthritis - joints should be able to go through FROM without substantial pain and there should not be an effusion, if there is a possibility the joint is the source, d/w orthopaedics BEFORE starting antibiotics unless patient has severe sepsis (ortho usually want a joint aspirate or washout in theatre first)
osteomyelitis - this is usually from a penetrating injury but may be haematogenous spread (eg. salmonella), if suspected, xray and perhaps nuclear med scan
thrombophlebitis erythema and tenderness tends to be linearly oriented over a vein
acute limb ischaemia although present usually as painful, pallor rather than erythema, check distal pulses
erythema migrans
Mx in ED
once doctor is happy there are no complicating factors and the above are addressed:
if leg cellulitis, strict elevation of leg to improve circulation and healing, and consider prophylactic enoxaparin to prevent deep venous thrombosis (DVT)
if the cellulitis is early, the patient is well, then the patient may be suitable for a trial of oral antibiotics (eg. flucloxacillin or cephalexin) +/- initial stat iv dose (eg. long acting antibiotic such as cephazolin)
otherwise, admit into short stay unit for iv antibiotics +/- hospital in the home, then if improved a course of oral antibiotics
usually need 5 days of iv antibiotics (eg. cephazolin 1-2g bd if managed by HITH nurses)
remember to Rx the cause such as tinea pedis
preferred choices of oral antibiotics
possible Staph:
flucloxacillin, or clindamycin if penicillin sensitive
NB. cefalexin has poor coverage for Staph aureus
most likely Strept:
cefalexin may be an option as better tolerated than the above
water-borne infections
those acquired in sea water could be caused by Vibrionaceae including Shewanella sp
those acquired in fresh water could be caused by Aeromonas sp
may need ciprofloxacin 500mg o bd or 400mg iv bd for at least 14 days +/- merepenem if severe
other unilateral cellulitis
these cases are likely to warrant further Ix or prolonged Rx and are usually best referred to general medicine rather than admission into a short stay unit where they are likely to block patient flow in the ED
they should be assessed as for simple cellulitis above, looking to exclude and address potential differentials or complications.
"bilateral leg cellulitis"
in the absence of trauma to both legs, rarely does cellulitis start on both legs simultaneously and rarely starts on one leg and jumps to the other
as a general rule these patients do not have cellulitis but another disorder often grouped as “pseudocellulitis” such as:
patients with bilateral chronic leg oedema from the many causes of this are most likely to have florid venous dermatosis, although uncommonly could have extensive DVTs
venous stasis dermatosis due to chronic oedema can cause the intense red discoloration on the shins, without sharp lines of demarcation, that is the hallmark of non infectious leg oedema, unfortunately they may temporarily improve on admission but this is due to leg elevation not the antibiotics leading to further confusion
one should not miss classic conditions such as:
urticaria
erythema nodosum - tender discrete red nodules on mainly anterior aspects lower legs
sunburn
contact dermatitis - this is a common cause of increasing pain, erythema in patients with stasis dermatosis, especially if topical creams or antibiotics have been used
xerotic eczema - itchy, dry lake bed like skin lesions over shins (eg. elderly excessive bathing or legs close to heaters), may become weepy dermatitis