Ruling out Cellulitis

Certain conditions affecting the lower limb can have similar symptoms to cellulitis.

If a patient has symptoms such as oedema or erythema but does not have a raised temperature, raised CRP or WBC, then it is unlikely to be cellulitis (Beldon & Burton, 2005). Other common conditions that may look similar with unilateral redness and or swelling and should be ruled out are:

Condition	Characteristics
Deep vein thrombosis	Characterised by pain, swelling of the calves without significant redness.
Septic arthritis	Involvement of the joint and disproportionate pain with joint movement.
Acute gout	Swelling, redness, warmth, and pain on passive movement. The skin around the joint may be inflamed.
Thrombophlebitis	Venous inflammation with thrombus formation. May cause redness, inflammation, and pain.
Cutaneous abscess	Hot, red, swollen, and painful swelling, which may need incision and drainage.
Erysipelas	Form of cellulitis involving more superficial dermal structures distinguished clinically by raised and well demarcated borders.
Gravitational eczema	Itch, non-tender erythema and sometimes areas of brown discoloration. Can become infected, which occasionally evolves into a secondary cellulitis.
Varicose eczema	Venous insufficiency — crusting, scaling, and itching.
Contact allergic dermatitis	Can present acutely as erythematous, sore, and tender areas of skin, sometimes with blisters.
Lipodermatosclerosis	Painful, red, tender, warm, hard, and sometimes scaly rash that occurs in the absence of significant systemic upset. It is most likely to occur in the lower leg in obese women with venous insufficiency.
Lymphoedema	Swelling (especially in the subcutaneous tissues) that occurs because of excess accumulation of lymph due to inadequate drainage.
Panniculitis	Inflammation of subcutaneous adipose tissue. Causes multiple tender nodules and plaques.
Oedema with blisters	Swelling with visible serous fluid filled blisters.

Adapted from (CKS NICE, 2023; PCDS, 2023)

Other less common conditions to consider, include:

Condition	Characteristics
Drug reactions	Itching and burning. There is usually a well-demarcated area of involvement and a history of similar reaction with prior exposure to the same drug.
Necrotising fasciitis	Destructive and rapidly progressive soft tissue infection that involves the deep subcutaneous tissues, fascia, and occasionally muscles. The presenting signs are usually non-specific (redness, swelling, and pyrexia). The person is usually systemically very unwell and has disproportionate pain.
Metastatic cancer	Fixed, red patch often with a raised edge and oedema due to lymphatic obstruction.
Wet gangrene	Ischaemia of tissue with adjacent cellulitis due to putrefaction of dead tissue.
Pyoderma gangrenosum	Small, tender pustules or papules that ulcerate with a purple undermined edge and surrounding redness, typically on the trunk or legs.
Erythema nodosum	Painful, red, warm nodules and plaques on the shins, knees, and ankles.
Eosinophilic cellulitis (Wells syndrome)	Rare - presents with large, indurated erythematous plaques, and less commonly nodules, that evolve over several weeks. Most people have a blood eosinophilia.
Eosinophilic fasciitis	Rare - cutaneous manifestations of eosinophilic fasciitis evolve as the condition progresses. The acute inflammatory stage consists of pain, swelling and tenderness of the distal limbs. These findings are later replaced by induration, and eventually fibrosis with limitation of the movement of the hands and feet. The affected skin is taut and firmly adherent to underlying tissue with dimpling and a peau d'orange appearance. The condition has a symmetrical distribution. There is a blood eosinophilia in 70% of cases.

Adapted from (CKS NICE, 2023; PCDS, 2023)