Differential Diagnosis for Cat Scratch to the Eye (not cornea)

• Single most likely diagnosis
  • Cat scratch disease (Bartonellosis): This is the most likely diagnosis due to the direct exposure to a cat scratch. The bacteria Bartonella henselae is commonly found in cats and can be transmitted through scratches, leading to infection.
• Other Likely diagnoses
  • Conjunctivitis: A cat scratch can introduce bacteria into the eye, leading to conjunctivitis, which is an inflammation of the conjunctiva.
  • Cellulitis: The scratch can also lead to a bacterial infection of the skin and soft tissues around the eye, resulting in cellulitis.
  • Allergic reaction: Some individuals may be allergic to the proteins in cat saliva or skin, leading to an allergic reaction around the eye.
• 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 can potentially transmit the virus, which is almost always fatal if not treated promptly.
  • Tularemia: Francisella tularensis, the bacteria that cause tularemia, can be found in cats and transmitted through scratches, leading to a potentially life-threatening infection.
  • Pasteurella multocida infection: This bacteria is commonly found in the mouths of cats and can cause severe infections, including sepsis, if not treated properly.
• Rare diagnoses
  • Erysipeloid: A rare bacterial infection caused by Erysipelothrix rhusiopathiae, which can be transmitted through animal scratches.
  • Sporotrichosis: A fungal infection caused by Sporothrix schenckii, which can be transmitted through scratches from animals that have come into contact with contaminated soil.