Differential Diagnosis

• Single most likely diagnosis
  • Cat scratch disease: This is the most likely diagnosis given the patient's history of petting a stray cat and the subsequent development of a red, itchy patch near her right eye. The incubation period of cat scratch disease, which is typically 3-10 days, also fits with the timeline provided.
• Other Likely diagnoses
  • Contact dermatitis: This could be a possible diagnosis if the patient is allergic to the cat's dander or saliva, which caused an allergic reaction when she petted the cat.
  • Impetigo: This is a contagious skin infection that could be spread through contact with an infected animal, although it's less likely given the initial presentation.
  • Insect bite reaction: The patient may have been bitten by an insect, such as a mosquito or flea, which was on the cat, causing a localized reaction.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Rabies: Although rare, rabies is a potentially deadly disease that can be transmitted through the bite or scratch of an infected animal. It's essential to consider this diagnosis, especially if the patient hasn't been vaccinated against rabies.
  • Tularemia: This is a bacterial infection that can be transmitted through contact with infected animals, including cats. It can cause skin ulcers, fever, and other systemic symptoms.
• Rare diagnoses
  • Erysipeloid: This is a rare bacterial infection that can be transmitted through contact with infected animals, including cats. It typically causes a well-demarcated, red lesion on the skin.
  • Sporotrichosis: This is a rare fungal infection that can be transmitted through contact with infected animals or contaminated soil. It typically causes a skin lesion that can ulcerate and spread along lymphatic channels.