Differential Diagnosis for Sore Throat, Headache, Fever, Erythema to Throat, and Allergic to PCN

• Single Most Likely Diagnosis
  • Viral pharyngitis: This is the most common cause of sore throat and is often accompanied by headache, fever, and erythema of the throat. The patient's allergy to penicillin (PCN) does not directly influence this diagnosis since viral infections do not require antibiotic treatment.
• Other Likely Diagnoses
  • Streptococcal pharyngitis (caused by Group A beta-hemolytic streptococcus): Although the patient is allergic to PCN, which is a common treatment for streptococcal infections, this diagnosis must be considered due to its potential for serious complications if left untreated. Alternative antibiotics can be used.
  • Mononucleosis (infectious mononucleosis): Caused by Epstein-Barr virus, this condition can present with sore throat, fever, headache, and sometimes a rash, which might be mistaken for erythema. It's more common in younger individuals.
• Do Not Miss Diagnoses
  • Epiglottitis: Although less common, epiglottitis is a potentially life-threatening condition that requires immediate attention. It can cause severe sore throat, difficulty swallowing, fever, and in severe cases, airway obstruction. The patient's allergy to PCN is irrelevant to the urgency of diagnosing and treating this condition.
  • Lemierre's syndrome: A rare but serious condition that starts with pharyngitis and can progress to septicemia and thrombophlebitis of the internal jugular vein. It's crucial to consider this diagnosis due to its high morbidity and mortality if not promptly treated.
• Rare Diagnoses
  • Diphtheria: A bacterial infection caused by Corynebacterium diphtheriae, characterized by a sore throat, fever, and a distinctive greyish membrane covering the tonsils and throat. It's rare in areas with high vaccination coverage but should be considered in travelers or individuals from areas with low vaccination rates.
  • Gonococcal pharyngitis: Caused by Neisseria gonorrhoeae, this condition can present with sore throat and is more common in sexually active individuals. It's a rare cause of pharyngitis but is important to consider due to its implications for sexual health and the need for appropriate treatment and contact tracing.