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Cellulitis - Cellulitis DDx
See also in: Overview,Anogenital,Hair and Scalp,Oral Mucosal Lesion
Other Resources UpToDate PubMed

Cellulitis - Cellulitis DDx

See also in: Overview,Anogenital,Hair and Scalp,Oral Mucosal Lesion
Contributors: Sabrina Nurmohamed MD, Susan Burgin MD
Other Resources UpToDate PubMed


Cellulitis is a common bacterial infection of the deep dermis and subcutaneous tissue characterized by erythema, pain, warmth, and swelling. Pathogens of cellulitis are strongly correlated with age and immune status:
  • Immunocompetent adults: Staphylococcus aureus and Streptococcus pyogenes. Staphylococcus aureus is the most frequent etiology in children and in purulent cellulitis.
  • Immunocompromised individuals, including those with diabetes and decubitus ulcers: mixture of gram-positive cocci and gram-negative aerobes and anaerobes.
A focused history should determine immune status, comorbid conditions, possible sites and causes of skin barrier disruption, prior history of cellulitis, and methicillin-resistant S. aureus (MRSA) risk factors. The most common route of bacterial seeding in immunocompetent individuals is via direct inoculation, and in immunocompromised individuals, it is via hematogenous seeding. Risk factors include minor skin trauma, body piercing, intravenous drug use, tinea pedis infection, animal bites, peripheral vascular disease, immune suppression (chronic systemic steroid use, neutropenia, immunosuppressive medications, alcohol use disorder), and lymphatic damage (lymph node dissection, radiation therapy, vein harvest for coronary artery bypass surgery, and damage that occurs following multiple prior episodes of cellulitis). Implantable cardiac devices can also cause infection.

Fevers, chills, and malaise often precede the onset of cellulitis. Poorly defined borders, erythema, swelling, tenderness, and warmth characterize typical cellulitis lesions. In adults, the extremities are the most common sites affected. In more severe cases, additional clinical features may include vesicle and bulla formation, pustules, and necrosis. Complications are not common but can include glomerulonephritis, lymphadenitis, and subacute bacterial endocarditis.

A rising prevalence of MRSA has been identified as a pathogen of skin and soft tissue infections in otherwise healthy individuals lacking the aforementioned risk factors for cellulitis. MRSA should be considered for penetrating traumas, purulent infections, and in specific populations: athletes, children, prisoners, military service members, long-term care residents, and intravenous drug users. Other MRSA risk factors include recent admission to a health care facility, presence of an indwelling catheter, poor personal hygiene, and history of MRSA.

Note: Cellulitis virtually never occurs bilaterally at the same time. If redness and involvement of the legs are bilateral in a patient suspected to have cellulitis, consider an alternative diagnosis such as stasis dermatitis or contact dermatitis.

Related topics: Orbital Cellulitis, Preseptal Cellulitis


L03.90 – Cellulitis, unspecified

128045006 – Cellulitis

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Differential Diagnosis & Pitfalls

Cellulitis can be caused by many different bacterial pathogens, but the diagnosis of typical cellulitis is almost always made clinically. If a patient has had more than 1 episode of cellulitis, investigate risk factors for recurring cellulitis but also consider alternative diagnoses.

Stasis dermatitis is a frequent cause of recurring severe leg or foot redness. There are usually no systemic signs or leukocytosis; commonly it is bilateral with pruritus and pigmentary changes.

Also consider:
  • Insect bite reactions
  • Contact dermatitis – Look for well-demarcated, weeping erythematous and pruritic plaques. Vesicles and bullae can be present. Usually no associated systemic signs.
  • Erysipelas – Well-defined erythematous plaque; associated with fever, chills, malaise.
  • Erythema nodosum (panniculitis) – Tender, indurated, multifocal, less superficial, and no epidermal changes.
  • Urticaria
  • Herpes infections (herpes simplex) with associated lymphangitic erythema.
  • Lipodermatosclerosis – Look for signs of chronic venous hypertension. A skin biopsy will confirm this diagnosis.
  • Fixed drug eruption
  • Gout
  • Vasculitis
  • Thrombophlebitis – No fever; tenderness and erythema overlying a palpable cord.
  • Tinea pedis
  • Impetigo – Honey-colored serous crusting.
  • Atopic dermatitis – Chronic course; pruritic and scaly.
  • Necrotizing fasciitis – Look for a violaceous hue, bullae or necrosis, and severe localized pain. Pain is out of proportion to physical exam and extends beyond the area of erythema. Anesthesia and malodorous fluid are associated features. Does not respond to antibiotics alone and requires surgical debridement. Rapidly progressive. Consider MRI to delineate soft tissue involvement.
  • Deep vein thrombosis – Rule out with ultrasound; decreased unilateral distal pulses, pain with ambulation, usually with little or no erythema.
  • Myonecrosis (gas gangrene) – Rapidly progressive; commonly occurs post surgical intervention; Clostridium perfringens isolated in over 80% of cases.
  • Herpes zoster – Pain and burning; unilateral and usually dermatomal; 10%-12% multidermatomal; grouped vesicles on an erythematous base.
  • Lyme disease (erythema chronica migrans) – Erythema, minimal edema, slow spreading over weeks.
  • Necrotizing fasciitis
  • Eosinophilic cellulitis
  • Osteomyelitis
  • Abscess

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Last Reviewed:08/10/2017
Last Updated:05/20/2019
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