Differential Diagnosis

• Single most likely diagnosis:
  • Infectious Mononucleosis (IMN): Justification - The patient's symptoms of swollen tonsils with white spots or patches, bilateral neck lymphadenopathy, and the timeline of these symptoms resolving, along with the initial absolute lymphocytosis followed by mild lymphocytosis and then normalization, are consistent with IMN, typically caused by Epstein-Barr virus (EBV). The patient's rapid improvement and the fact that these symptoms appeared after a potential exposure (though the exact nature of the exposure is not specified) also support this diagnosis. The negative HIV tests further reduce the likelihood of an HIV-related condition, which can also present with similar symptoms.
• Other Likely diagnoses:
  • Acute Viral Pharyngitis: Justification - This could explain the initial symptoms of swollen tonsils and lymphadenopathy. However, the presence of absolute lymphocytosis and the subsequent evolution of symptoms make IMN more likely.
  • Streptococcal Pharyngitis: Justification - Although the patient was taking Amoxicillin, which would be appropriate for streptococcal infections, the lymphocytosis and the overall clinical picture are more suggestive of a viral etiology.
  • Toxoplasmosis: Justification - This infection can cause lymphadenopathy and mild lymphocytosis, but it is less likely given the acute presentation and the resolution of symptoms without specific treatment for toxoplasmosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.):
  • HIV Infection (Acute Retroviral Syndrome): Justification - Despite the negative HIV tests, the possibility of a very early HIV infection or a false-negative result (especially if the tests were done very early in the course of the infection) cannot be entirely ruled out without further testing, including a repeat test after an appropriate window period. The patient's reported negative HIV status and the timing of the symptoms in relation to the potential exposure are critical.
  • Lymphoma: Justification - Although less likely given the rapid resolution of lymphadenopathy and the absence of systemic symptoms like weight loss or night sweats, lymphoma can present with lymphadenopathy and should be considered, especially if there are residual or hard lymph nodes.
• Rare diagnoses:
  • Cytomegalovirus (CMV) Infection: Justification - CMV can cause a mononucleosis-like syndrome, but it is less common than EBV and would typically be considered if the patient was immunocompromised or if EBV serologies were negative.
  • Other viral infections (e.g., adenovirus, herpes simplex virus): Justification - These can cause similar symptoms but are less commonly associated with significant lymphocytosis and lymphadenopathy.