Differential Diagnosis for 2 yo with Painful Vesicles on Gums and Lips

• Single most likely diagnosis:
  • Herpes Simplex Virus (HSV) infection: This is the most common cause of painful vesicles on the gums and lips in a 2-year-old, often presenting as primary herpetic gingivostomatitis.
• Other Likely diagnoses:
  • Hand, Foot, and Mouth Disease (HFMD): Caused by viruses like Coxsackievirus A, this condition can also present with vesicles on the gums and lips, though it more commonly affects the hands and feet.
  • Varicella-Zoster Virus (VZV) infection: Although more commonly associated with a rash on the trunk and extremities, VZV can cause oral lesions, especially if the child has not been vaccinated.
• Do Not Miss diagnoses:
  • Erythema Multiforme (EM): A potentially life-threatening condition that can be triggered by HSV or other infections, characterized by target lesions on the skin and sometimes mucous membranes.
  • Stevens-Johnson Syndrome (SJS) or Toxic Epidermal Necrolysis (TEN): These are severe skin and mucous membrane disorders, usually a reaction to medication or infection, which can present with oral lesions and are medical emergencies.
• Rare diagnoses:
  • Autoimmune disorders like Pemphigus Vulgaris: Although rare in children, this autoimmune disease can cause blistering of the skin and mucous membranes.
  • Behçet's Disease: A rare condition that can cause oral ulcers, among other symptoms, but is uncommon in young children.
  • Primary Immunodeficiency Diseases: Certain immunodeficiencies can predispose children to more severe or recurrent infections, including those causing oral vesicles.