Differential Diagnosis

The patient's symptoms of fever, conjunctivitis, cough, vomiting, diarrhea, papulopustular rash, and oral mucosa ulceration suggest a complex and potentially infectious or autoimmune etiology. Here's a categorized differential diagnosis:

• Single most likely diagnosis
  • Infectious Mononucleosis: Given the combination of fever, cough, conjunctivitis, and particularly the presence of a rash and oral mucosa ulceration, infectious mononucleosis (caused by Epstein-Barr virus) is a strong consideration. The patient's age and general well-being before the illness also align with this diagnosis.
• Other Likely diagnoses
  • Stevens-Johnson Syndrome (SJS): The presence of a papulopustular rash, especially on the face, along with mucosal involvement (oral ulceration) and systemic symptoms like fever, could suggest SJS, a severe skin and mucous membrane disorder often triggered by an infection or medication.
  • Influenza with secondary bacterial infection: The initial symptoms of fever, cough, and slight crepitations could indicate influenza, with the potential for secondary bacterial pneumonia, especially given the chronic cough history.
  • Gastroenteritis with extraintestinal manifestations: The gastrointestinal symptoms (vomiting and diarrhea) could be primary, with the other symptoms representing extraintestinal manifestations of a gastrointestinal infection.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Meningococcemia: Although less likely given the full spectrum of symptoms, meningococcemia can present with fever, rash, and severe systemic illness. It's critical to consider this diagnosis due to its high mortality rate if not promptly treated.
  • Toxic Shock Syndrome: The combination of fever, rash, and multi-system involvement (including gastrointestinal and respiratory symptoms) could suggest toxic shock syndrome, a life-threatening condition that requires immediate intervention.
  • Pneumonia with sepsis: The respiratory symptoms and slight crepitations, in combination with systemic symptoms like fever and vomiting, could indicate pneumonia complicated by sepsis, a condition that necessitates urgent medical attention.
• Rare diagnoses
  • Erythema Multiforme: A skin condition characterized by target lesions, which could be considered given the rash and mucosal involvement, though it's less likely than SJS given the description.
  • Behçet's Disease: A form of vasculitis that can present with oral ulcers, skin lesions, and eye inflammation, among other symptoms. It's a rare condition and would be less likely without additional specific findings like genital ulcers or a history suggestive of recurrent episodes.