Infectious Mononucleosis (Mono): This condition, caused by Epstein-Barr virus (EBV), often presents with sore throat, lymphadenopathy, and can be associated with erythema multiforme, especially in the context of a viral infection triggering the skin condition.

Streptococcal Infection: Streptococcal pharyngitis can lead to sore throat and lymphadenopathy. Erythema multiforme can occasionally be triggered by streptococcal infections, making this a plausible diagnosis.
Viral Exanthem: Various viral infections can cause exanthems (rashes) that might resemble erythema multiforme, along with sore throat and lymphadenopathy, due to the body's immune response to the virus.

Lymphoma: Although less common, lymphoma can present with lymphadenopathy and systemic symptoms. The presence of erythema multiforme, while rare, has been associated with lymphoma in some cases, making it crucial not to miss this potentially life-threatening diagnosis.
HIV Infection: Acute HIV infection can manifest with a variety of symptoms, including sore throat, lymphadenopathy, and rash. Given the significant implications of HIV infection, it is essential to consider this diagnosis.
Autoimmune Disorders (e.g., Lupus): Systemic lupus erythematosus (SLE) and other autoimmune disorders can present with a wide range of symptoms, including skin rashes (potentially resembling erythema multiforme), lymphadenopathy, and sore throat, due to the body's immune system attacking its own tissues.

Kawasaki Disease: Although more common in children, Kawasaki disease can present with fever, lymphadenopathy, and a rash, which might be confused with erythema multiforme. It's a rare but important consideration due to its potential for cardiac complications.
Drug Reaction with Eosinophilia and Systemic Symptoms (DRESS): This is a rare but severe drug reaction that can cause rash, lymphadenopathy, and systemic symptoms, including sore throat. It's essential to consider in patients recently started on new medications.