Differential Diagnosis

• Single most likely diagnosis
  • Erythema Multiforme: This condition is characterized by target-like lesions with a dusky red center, which matches the patient's presentation. The presence of a recent cold sore (herpes simplex infection) is also a common trigger for erythema multiforme.
• Other Likely diagnoses
  • Contact Dermatitis: Although the patient's rash is not itchy, which is unusual for contact dermatitis, it's still possible, especially given her occupation as a personal trainer where she may be exposed to various substances at the gym.
  • Vesiculopapular rash (possibly Herpes Simplex): Given the patient has had a cold sore, it's possible that the rash on her hands could be related to a herpes simplex infection, although this is less common.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Secondary Syphilis: This condition can cause a rash on the palms and soles, although it's less common. Given the potential severity of untreated syphilis, it's crucial not to miss this diagnosis.
  • Rocky Mountain Spotted Fever (RMSF): Although rare, RMSF can cause a rash on the hands and feet and is critical to diagnose early due to its high mortality rate if left untreated.
• Rare diagnoses
  • Molluscum Contagiosum: This viral infection causes small, pearly, or flesh-colored lesions, which doesn't exactly match the patient's presentation of dusky red and white centers.
  • Scabies: Typically presents with intense itching and burrows, which doesn't fit the patient's description of a non-itchy rash.
  • Versicolor: A fungal infection that causes discolored patches on the skin, which doesn't match the target-like lesions described.