Differential Diagnosis for a 14-year-old Female with a Stingy Red Rash and Vesicles on the Bilateral Neck

• Single most likely diagnosis:
  • Contact Dermatitis: This is likely due to an allergic reaction or irritant from an external source, possibly related to playing outside, such as plants (e.g., poison ivy, oak, or sumac) or an insect bite. The absence of fever and the localized nature of the rash support this diagnosis.
• Other Likely diagnoses:
  • Sunburn: Although the mother suspects sunburn, the presence of vesicles is less typical for sunburn, which usually presents with erythema and sometimes blistering but not typically vesicles. However, it cannot be ruled out without further history or examination.
  • Insect Bites: Multiple bites from insects like mosquitoes or bed bugs could cause a similar appearance, especially if the reaction is severe.
  • Eczema (Atopic Dermatitis): If the patient has a history of atopic diseases (asthma, allergies), eczema could be a consideration, though the acute onset and localization to the neck might be less typical.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): Although rare and usually associated with medication use or infections, these conditions can present with skin lesions and are medical emergencies. The lack of fever and new medication use makes this less likely, but it's crucial to monitor for any signs of worsening or systemic involvement.
  • Herpes Zoster (Shingles): Uncommon in this age group without immunocompromise, but could present with a vesicular rash. Typically, it's dermatomal and accompanied by pain.
• Rare diagnoses:
  • Pemphigus Vulgaris: An autoimmune disease that can cause blistering of the skin and mucous membranes. It's rare and usually seen in older adults, making it an unlikely diagnosis in a 14-year-old.
  • Bullous Pemphigoid: Another autoimmune blistering disease, more common in elderly individuals, which could present with vesicles and erythema but is rare in adolescents.
  • Dermatitis Herpetiformis: Associated with celiac disease, it presents with intensely itchy, blistering skin. The diagnosis would require further investigation into gastrointestinal symptoms and serological tests for celiac disease.