Unusual clinical course of infectious mononucleosis: Complicating bilateral peritonsillar abscess

Background: Infectious mononucleosis (IM) caused by Epstein-Barr virus typically presents with fever, pharyngitis, and lymphadenopathy, and most patients recover within a few weeks. However, bilateral peritonsillar abscess is a rare but serious complication of IM that can lead to airway compromise and descending mediastinitis. Due to its rarity and similarity in clinical presentation of IM, it may be challenging to diagnose bilateral peritonsillar abscess during the course of IM. Case report: A 21-year-old healthy male who initially presented with fever, sore throat, and abdominal discomfort for ten days was diagnosed with IM based on clinical and laboratory findings. Despite initial treatment, the patient returned to the emergency department three times within one week due to persistent symptoms, and on the third visit, he had difficulty opening his mouth and had worsening odynophagia. Contrast-enhanced computed tomography revealed bilateral peritonsillar abscess, and an emergent incision of the right tonsil was performed. Bacterial culture revealed multiple oral organisms. He was diagnosed with bilateral peritonsillar abscess associated with IM and was discharged without complications. Why should an emergency physician be aware of this?: This case highlights two important clinical issues: the potential for patients with IM to develop bilateral peritonsillar abscess and the significance of trismus and exacerbation of odynophagia as a clue for identifying this complication. The rarity of this complication may result in delayed diagnosis and treatment, leading to serious complications. Prompt diagnosis and treatment are crucial for preventing potentially life-threatening consequences.