Differential Diagnosis for Cat Scratch

• Single most likely diagnosis
  • Cat scratch disease (Bartonellosis): This is the most likely diagnosis due to the direct exposure to a cat scratch, which is a common mode of transmission for Bartonella henselae, the bacterium responsible for cat scratch disease.
• Other Likely diagnoses
  • Cellulitis: A bacterial infection of the skin and subcutaneous tissues, which can occur after a cat scratch, especially if the scratch becomes contaminated with bacteria.
  • Abscess: A localized collection of pus that can form as a result of a bacterial infection, potentially caused by bacteria introduced through the cat scratch.
  • Folliculitis: An inflammation of the hair follicles, which can be caused by bacterial infection, including those introduced by a cat scratch.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Rabies: Although rare, if the cat is infected with rabies, a scratch could potentially transmit the virus, making prompt recognition and treatment critical.
  • Tetanus: A bacterial infection caused by Clostridium tetani, which can enter the body through wounds, including deep scratches, and can be life-threatening if not treated.
• Rare diagnoses
  • Pasteurella multocida infection: A bacterium commonly found in the mouths of cats and dogs, which can cause infections in humans through bites or scratches, though it's less commonly associated with scratches than bites.
  • Capnocytophaga canimorsus infection: A bacterium found in the mouths of dogs and cats, which can cause severe infections in humans, particularly those who are immunocompromised, though it's more commonly associated with dog bites.