Cellulitis

[Clin Infect Dis 2014;59;e10-52]

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Minimum criteria for cellulitis:

• redness, and

• warmth, and

• swelling, and

• pain, and

• unilateral involvement.

- If purulence/abscess, see Skin Abscess.

Cellulitis includes:

• erysipelas – acute, superficial, nonnecrotizing infection of dermis/hypodermis typically caused by streptococci. Classically presents with well defined raised edge/erythematous plaque of sudden onset associated with pain, swelling and fever.

• cellulitis - acute, subacute or chronic nonnecrotizing infection of dermis/ hypodermis that extends into the subcutaneous/connective tissues with/without lymphadenopathy and/or abscess formation.

Investigations:

- Superficial skin cultures not recommended.

Exceptions:

• subcutaneous abscess present: incision and drainage with culture recommended.

• toe web intertrigo: culture of fissures may yield pathogen (β-hemolytic strep/S. aureus/MRSA) to help guide treatment. Also culture for dermatophytes and treat if positive as may be source of bacterial entry/recurrence.

- In moderate-severe cellulitis (extensive involvement, systemic symptoms), WBC and CRP recommended.

- Blood cultures recommended if septic, temp ≥ 38.5°C, chills/rigors, lymphangitis, elevated lactate, WBC > 15x10⁹/L, or immunocompromised.

Most Common Differential Diagnosis:

Unilateral Cellulitis

• Deep vein thrombosis/superficial thrombophlebitis

• Contact dermatitis (may be bilateral)

• Drug reactions (often sulfa-based drugs)

• Gout

• Erythema migrans

• Pyoderma gangrenosum (anterior shin/ulcerative)

• Relapsing polychondritis (ears)

• Polyarteritis nodosa (lower extremities)

Bilateral Cellulitis

NB: rare condition; always consider alternate diagnosis

• Venous stasis (most common misdiagnosis of cellulitis)

• Contact dermatitis (may be unilateral)

• Lymphedema with chronic inflammation

• Neuropathic arthropathy (acute Charcot joint) – always consider in neuropathic patients

• Hemosiderin staining/Lipodermatosclerosis

• Peripheral vascular disease – may need urgent vascular surgery consult

Other Less Common Diagnoses to Consider:

• Toxic epidermal necrolysis

• Eosinophilic cellulitis (Well's syndrome)

• Acute febrile neutrophilic dermatosis (Sweet's syndrome)

• Erythema nodosum

• Carcinoma erysipeloides

• Foreign body reactions

• Myositis (viral/parasitic)

• Familial Mediterannean Fever

Management:

• Elevation of affected limb essential:

  • lower extremity – elevate higher than hip joint

  • upper extremity – elevate higher than shoulder.

- Assess response to initial antibiotic therapy at 3 days.

NB: Increased redness/extension of cellulitis may occur after initiation of antibiotic therapy (due to release of toxins); NOT a reliable marker of clinical status if otherwise improving.

- In moderate-severe cellulitis (extensive involvement, systemic symptoms), a decrease in WBC and/or CRP are useful markers to assess clinical improvement.