Differential Diagnosis

Based on the signs and symptoms provided, the differential diagnosis can be categorized as follows:

• Single Most Likely Diagnosis

  • Infectious Mononucleosis (Mono): This condition, caused by the Epstein-Barr virus (EBV), is characterized by a gradual onset of low-grade fever, marked fatigue, severe sore throat, and posterior cervical lymphadenopathy, closely matching the patient's symptoms.

• Other Likely Diagnoses

  • Streptococcal Pharyngitis: Although it typically presents with a more acute onset, streptococcal pharyngitis can cause severe sore throat and fever. The presence of posterior cervical lymphadenopathy can also be seen in this condition.
  • Acute HIV Infection: The acute retroviral syndrome can present with fever, fatigue, sore throat, and lymphadenopathy, making it a consideration in the differential diagnosis.
  • Toxoplasmosis: Infection with Toxoplasma gondii can cause a mononucleosis-like syndrome, including lymphadenopathy and fever, especially in immunocompetent individuals.

• Do Not Miss Diagnoses

  • Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can present with lymphadenopathy, fever, and fatigue. Although less common, missing this diagnosis could have severe consequences.
  • Tuberculosis (TB): TB can cause lymphadenopathy, fever, and fatigue. It's particularly important to consider in individuals with risk factors for TB exposure.
  • Leukemia: Certain types of leukemia, such as acute lymphoblastic leukemia (ALL), can present with symptoms similar to those described, including lymphadenopathy and fatigue.

• Rare Diagnoses

  • Cytomegalovirus (CMV) Mononucleosis: Similar to EBV, CMV can cause a mononucleosis syndrome, but it's less common and typically seen in specific populations, such as immunocompromised individuals or those with certain occupational exposures.
  • Human Herpesvirus 6 (HHV-6) Infection: HHV-6 can cause a mononucleosis-like illness, but it's relatively rare and often associated with specific clinical contexts, such as immunosuppression.
  • Brucellosis: This zoonotic infection can cause fever, fatigue, and lymphadenopathy but is relatively rare and usually associated with specific occupational or travel exposures.