History

Fact Explanation
Pruritic skin lesions Due to infection by staphylococcus aureus and group A streptococcus. Pruritus is seen especially if associated with atopic dermatitis, ie. owing to the inflammation [1].
History of predisposing factors: injury to skin, genetic & inflammatory conditions and cutaneous infections These predisposing factors act as portals of entry for pathogenic organisms. Minor cuts / ulcers cause primary impetigo while atopic dermatitis / insect bites / porphyria cutania tarda / sunburn / bullous pemphigoid / chronic lymphedema / cutaneous infections with herpes simplex, varicella zoster, herpes zoster and dermatophytes cause secondary impetigo [1].
References
  1. WOLFF, Klaus. Richard Allen JOHNSON. Fitzpatrick’s Color atlas and synopsis of clinical dermatology. 6th edition. Singapore: McGraw-Hill, 2009.

Examination

Fact Explanation
Non-bullous impetigo: Skin lesions are 1-3 cm size erosions with golden crusting. Central healing and satellite lesions may be present. Satellite lesions occur by autoinoculation [1]. Usually there are multiple lesions in a single patient, mostly involving the face [2]. Note: The golden/honey color of the lesions is not a distinguishing feature of impetigo, as there are other causes for this presentation as well [1].
Bullous impetigo: skin lesions are bullae and vesicles containing fluid/pus, with surrounding erythema. Exfoliative toxins of staphylococcus aureus produce blistering by cleaving cell adhesion molecules. When the bullae are ruptured yellowish exudate is released, followed by crust formation [2]. This is considered the localized form of staphylococcal scalded skin syndrome [3].
Underlying skin conditions predisposing to impetigo may be observed. Patients with atopic dermatitis / sunburns / abrasions / lymphedema / ulcers are more prone to develop impetigo, as a breach in the skin is essential for staphylococcal infection [2].
References
  1. WOLFF, Klaus. Richard Allen JOHNSON. Fitzpatrick’s Color atlas and synopsis of clinical dermatology. 6th edition. Singapore: McGraw-Hill, 2009.
  2. WELLER, Richard, John HUNTER, John SAVIN, Mark DAHL. Clinical Dermatology. Fourth Edition. Singapore: Blackwell Publishing, 2008.
  3. ELIAS, Peter M., S. William LEVY. Bullous Impetigo. Archives of Dermatology [Online]. American medical association. June 1976, 112,856-8 [viewed 18 March 2014].

Differential Diagnoses

Fact Explanation
Allergic contact dermatitis Produces bullae, erosions and crusting in severe lesions. May have pruritus [1].
Herpes simplex viral infection Usually causes vesicular lesions. May even cause patches of erythema and erosions [1].
Dermatophytosis May form bullae. The site of the lesions are commonly the feet (tenia pedis), trunk (taenia corporis), groin (taenia cruiris), hands (taenia mannum), and the face is usually spared unlike in impetigo [1]. Taenia capitis is also an important differential to consider [2].
Scabies Causes itchy skin lesions which consist of nodules and burrows. May have eczematous dermatitis [1].
Thermal burns Causes blisters similar to bullous impetigo [1].
Bullous pemphigoid This is an autoimmune diseases that produces bullae and blisters associated with itching. Bullae are large and tense. Urticarial plaques may be seen in the surrounding skin[1].
Pediculosis (scalp lice) This is a cause of pruritus and excoriation in the area around the face and head. Important: always consider this differential in patients presenting with recurrent impetigo [3].
References
  1. WOLFF, Klaus. Richard Allen JOHNSON. Fitzpatrick’s Color atlas and synopsis of clinical dermatology. 6th edition. Singapore: McGraw-Hill, 2009.
  2. NOBLE, sara L., D. PHARM, Robert C. FORBES. Diagnosis and Management of Common Tinea Infections. American family physician [Online]. American academy of family physicians. July 1, 1998, 58(1), 163-174. [viewed 19 March 2014].
  3. WELLER, Richard, John HUNTER, John SAVIN, Mark DAHL. Clinical Dermatology. Fourth Edition. Singapore: Blackwell Publishing, 2008.

Investigations - for Diagnosis

Fact Explanation
Gram stain of the skin lesions Will show gram positive cocci in clusters in staphylococcal infection, and gram positive cocci in chains in streptococcal infection [1]. Note: the diagnosis is made clinically and can be confirmed by the investigations if required only [2].
Bacterial culture of the skin lesions Will show the growth of causative organisms [1].
References
  1. WOLFF, Klaus. Richard Allen JOHNSON. Fitzpatrick’s Color atlas and synopsis of clinical dermatology. 6th edition. Singapore: McGraw-Hill, 2009.
  2. COLE, Charles, John GAZEWOOD. Diagnosis and Treatment of Impetigo. American family physician [Online]. American academy of family physicians. March 15, 2007, 75,859-64[viewed 18 March 2014].

Management - General Measures

Fact Explanation
Preventive measures Daily bath with benzyl peroxide wash helps to eliminate methicillin resistant staphylococcus aureus (MRSA) [1]. Intranasal mupirocin ointment, chlorhexidine gluconate washes, oral doxycycline & rifampicin are also effective in eradicating MRSA. However, susceptibility testing should be done before starting treatment with mupirocin, due to the developing resistance [2].
References
  1. WOLFF, Klaus. Richard Allen JOHNSON. Fitzpatrick’s Color atlas and synopsis of clinical dermatology. 6th edition. Singapore: McGraw-Hill, 2009.
  2. SIMOR, Andrew E., Elizabeth PHILLIPS, Allison MCGEER, Ana KONVALINKA et al. Randomized Controlled Trial of Chlorhexidine Gluconate for Washing, Intranasal Mupirocin, and Rifampin and Doxycycline Versus No Treatment for the Eradication of Methicillin-Resistant Staphylococcus aureus Colonization. Clinical infectious diseases [Online]. Infectious diseases society of America. 2007, 44(2), 178-185 [viewed 18 March 2014]. Available from: doi: 10.1086/510392.

Management - Specific Treatments

Fact Explanation
Topical antibiotics Application of neomycin, fusidic acid, mupirocin or bacitracin after removal of the crust is sufficient for minor lesions [1]. Topical mupirocin is superior to oral erythromycin in eradicating MRSA [2]. Note: sometimes the lesions heal even without treatment [1].
Systemic antibiotics Flucloxacillin, erythromycin or cephalexin is needed for severe lesions. Penicillin V is used for streptococcal strains that are at risk of causing glomerulonephritis [1]. Note: resistance rates to erythromycin are rising and is considered to be less effective [3]. Oral cephalexin is considered the drug of choice for systemic treatment in children [4].
References
  1. WELLER, Richard, John HUNTER, John SAVIN, Mark DAHL. Clinical Dermatology. Fourth Edition. Singapore: Blackwell Publishing, 2008.
  2. MERTZ, Patricia M., David A. MARSHALL, William H. EAGLSTEIN, Yvette PIOVANETTI, Josephina MONTALVO. Topical Mupirocin Treatment of Impetigo Is Equal to Oral Erythromycin Therapy. Archives of Dermatology [Online]. American medical association. August 1989, 125,1069-73 [viewed 18 March 2014].
  3. COLE, Charles, John GAZEWOOD. Diagnosis and Treatment of Impetigo. American family physician [Online]. American academy of family physicians. March 15, 2007, 75,859-64[viewed 18 March 2014].
  4. BASS, James W., Debora CHAN, Kevin M. Creamer, Mark M. THOMPSON et al. COMPARISON OF ORAL CEPHALEXIN, TOPICAL MUPIROCIN AND TOPICAL BACITRACIN FOR TREATMENT OF IMPETIGO. The Pediatric Infectious Disease Journal [Online]. Williams & Wilkins. July 1997, 16(7), 708-710 [viewed 18 March 2014].