Category: Visual Diagnosis
41year-old male without past medical history presents with the image below. What's the diagnosis and what's the most likely causative organism?
Gram-Negative web-space infection; most common etiologic organism is Pseudomonas
Gram Negative Web-space Infections
Gram-negative infections may occur in toe web-spaces of healthy patients, especially in areas with hyperhidrosis (excessive perspiration) and macerated skin.
Common organisms include Pseudomonas; others include Corynebacterium minutissimum (causes erythrasma, chronic superficial infection of the intertriginous areas of the skin), and other gram-negative bacteria
Woods-light examination may be clinically helpful if Pseudomonas is suspected (fluoresce green) and erythrasma will fluoresce coral red. KOH direct examination for fungal elements may show the presence of dermatophytes or Candida.
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Wolff, K., & Johnson, R. J. (2009). Fitzpatrick's Color Atlas and Synopsis of Clinical Dermatology. (6th ed., pp. 662-664;698). McGraw-Hill.