eMedicine Specialties > Dermatology > Bacterial Infections

Impetigo: Differential Diagnoses & Workup

Author: Sadegh Amini, MD, Senior Clinical Research Fellow, Skin Research Group, Department of Dermatology and Cutaneous Surgery, Miller School of Medicine, University of Miami
Coauthor(s): Anne E Burdick, MD, MPH, Professor of Dermatology, Director of Leprosy Program, Associate Dean for TeleHealth and Clinical Outreach, University of Miami Miller School of Medicine
Contributor Information and Disclosures

Updated: Sep 8, 2009

Differential Diagnoses

Other Problems to Be Considered

Differentials
 
Bullous impetigo

Nonbullous impetigo

Workup

Laboratory Studies

  • Impetigo is usually diagnosed on the basis of clinical findings.
  • Bacterial culture and sensitivity are recommended (1) in cases to identify methicillin-resistant Staphylococcus aureus (MRSA), (2) if an outbreak of impetigo has occurred, or (3) if poststreptococcal glomerulonephritis is present. Exudate from underneath the crust is sent for culture.
  • Leukocytosis is present in approximately 50% of impetigo cases.
  • Antideoxyribonuclease (anti-DNAase) B antibody levels are often elevated in persons with streptococcal impetigo.
  • Urinalysis is necessary to evaluate for acute poststreptococcal glomerulonephritis if the patient develops new-onset edema or hypertension. Hematuria, proteinuria, and cylindruria are indicators of renal involvement.
  • A potassium hydroxide wet mount may be performed to exclude bullous dermatophyte infection.
  • A Tzanck preparation or viral culture may be performed to exclude herpes simplex infection.
  • A bacterial culture of the nares may be obtained to determine whether a patient is an S aureus carrier.
  • If the nares culture is negative and the patient has persistent recurrent episodes of impetigo, bacterial cultures should be obtained from the axillae, pharynx, and perineum.
  • Obtain serum IgM levels in cases of recurrent impetigo in patients with negative S aureus carrier status and no predisposing factors such as a preexisting dermatosis.11 Serum level determination of IgA, IgM, and IgG, including IgG subclasses, is necessary to rule out other immunodeficiencies.

Histologic Findings

In bullous impetigo, few or no inflammatory cells are present within the bulla. A polymorphous infiltrate is present in the upper dermis. Acantholysis is noted in the granular layer.

In nonbullous impetigo, a serum crust is present above the epidermis. Neutrophils are common within the crust. In addition, gram-positive cocci are seen. Epidermal spongiosis and a severe dermal infiltrate of neutrophils and lymphoid cells are seen.

More on Impetigo

Overview: Impetigo
Differential Diagnoses & Workup: Impetigo
Treatment & Medication: Impetigo
Follow-up: Impetigo
Multimedia: Impetigo
References
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Further Reading

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Keywords

impetigo, impetigo contagiosa, Fox impetigo, impetigo bullosa, impetigo contagiosa bullosa, impetigo neonatorum

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Contributor Information and Disclosures

Author

Sadegh Amini, MD, Senior Clinical Research Fellow, Skin Research Group, Department of Dermatology and Cutaneous Surgery, Miller School of Medicine, University of Miami
Sadegh Amini, MD is a member of the following medical societies: American Society for Dermatologic Surgery, International Society for Dermatologic Surgery, and International Society of Dermatology
Disclosure: Nothing to disclose.

Coauthor(s)

Anne E Burdick, MD, MPH, Professor of Dermatology, Director of Leprosy Program, Associate Dean for TeleHealth and Clinical Outreach, University of Miami Miller School of Medicine
Anne E Burdick, MD, MPH is a member of the following medical societies: Washington State Medical Association
Disclosure: Nothing to disclose.

Medical Editor

James J Nordlund, MD, Professor Emeritus, Department of Dermatology, University of Cincinnati College of Medicine
James J Nordlund, MD is a member of the following medical societies: American Academy of Dermatology, Sigma Xi, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

Pharmacy Editor

Michael J Wells, MD, Associate Professor, Department of Dermatology, Texas Tech University Health Sciences Center
Michael J Wells, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, and Texas Medical Association
Disclosure: Nothing to disclose.

Managing Editor

Paul Krusinski, MD, Director of Dermatology, Professor, Department of Internal Medicine, Fletcher Allen Health Care, University of Vermont
Paul Krusinski, MD is a member of the following medical societies: American Academy of Dermatology, American College of Physicians, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

CME Editor

Catherine M Quirk, MD, Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania
Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology
Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD, Director, Department of Dermatology, Geisinger Medical Center
Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology
Disclosure: Nothing to disclose.

 
 
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