Differential Diagnosis for 57-year-old Male with Acute Onset Seizure and Confusion

• Single most likely diagnosis:
  • Herpes Simplex Encephalitis (HSE): The presence of a cold sore (herpes labialis) and the acute onset of seizure and confusion are highly suggestive of HSE, especially given the fever and altered mental status. HSE is known for its rapid progression and severity, making it a prime consideration in this scenario.
• Other Likely diagnoses:
  • Bacterial Meningitis: Although the neck is supple and there are no meningeal signs, bacterial meningitis can present atypically, especially in older adults. The high fever and confusion warrant consideration of this diagnosis.
  • Viral Meningoencephalitis (other than HSE): Other viral infections could cause similar symptoms, including enteroviruses, arboviruses, and less commonly, influenza or COVID-19, depending on the epidemiological context.
  • Acute Stroke or Transient Ischemic Attack (TIA): Seizures can be a presenting feature of stroke, particularly in older adults. The sudden onset of symptoms could also suggest a vascular event.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed):
  • Subarachnoid Hemorrhage: Although less likely given the absence of headache or meningeal signs, subarachnoid hemorrhage can present with sudden onset of seizure and altered mental status. Missing this diagnosis could be catastrophic.
  • Brain Abscess: A brain abscess could cause focal neurological signs, seizures, and altered mental status, especially if it involves the frontal lobe. It's a less common diagnosis but critical to consider due to its severity and need for prompt treatment.
  • Status Epilepticus due to Other Causes: Prolonged or recurrent seizures can lead to status epilepticus, which is a medical emergency. Identifying and treating the underlying cause is crucial.
• Rare diagnoses:
  • Autoimmune Encephalitis: This is a group of conditions that can present with seizures, altered mental status, and sometimes fever, but they are less common and might be considered after more typical diagnoses are ruled out.
  • Prion Diseases: Although extremely rare, prion diseases like Creutzfeldt-Jakob disease can present with rapid neurological deterioration, including seizures and altered mental status. However, they typically have a more gradual onset and distinct features like myoclonus.
  • Mitochondrial Encephalomyopathies: These are a group of rare genetic disorders that affect the mitochondria and can cause a variety of neurological symptoms, including seizures and encephalopathy, but they usually have a more chronic course and other systemic involvement.