Template for Differential Diagnosis

When presenting a patient's symptoms, the following template can be used to organize the thought process:

• Single Most Likely Diagnosis: This category includes the diagnosis that is most probable based on the patient's presentation.
• Other Likely Diagnoses: These are diagnoses that are also plausible but less likely than the single most likely diagnosis.
• Do Not Miss Diagnoses: These are critical diagnoses that may not be the most likely but are potentially life-threatening or have significant morbidity if missed.
• Rare Diagnoses: These are less common conditions that could explain the patient's symptoms but are not as frequently encountered.

Example Application

For a hypothetical case of a patient presenting with fever, headache, and stiff neck, the differential diagnosis might be organized as follows:

• Single Most Likely Diagnosis
  • Viral meningitis: This is often the most common cause of meningitis, especially in younger adults, and presents with fever, headache, and neck stiffness.
• Other Likely Diagnoses
  • Bacterial meningitis: Although less common than viral meningitis, it is a critical diagnosis to consider due to its high morbidity and mortality if not treated promptly.
  • Viral encephalitis: Inflammation of the brain tissue, which can present similarly to meningitis but may have additional symptoms such as altered mental status or seizures.
• Do Not Miss Diagnoses
  • Subarachnoid hemorrhage: A life-threatening condition that can present with sudden onset of headache and may have associated neck stiffness, mimicking meningitis.
  • Brain abscess: A localized infection within the brain that can cause fever, headache, and focal neurological deficits.
• Rare Diagnoses
  • Fungal meningitis: More common in immunocompromised patients, this can present with similar symptoms to viral or bacterial meningitis but may have a more subacute onset.
  • Tuberculous meningitis: A rare form of meningitis caused by Mycobacterium tuberculosis, often presenting with a more gradual onset of symptoms.

Diagnostic Approach

• Labs to Order:
  • Complete Blood Count (CBC) to look for signs of infection or inflammation.
  • Blood cultures to identify any bacteremia.
  • Cerebrospinal fluid (CSF) analysis through lumbar puncture for cell count, glucose, protein, and culture to directly assess for meningitis.
• Imaging to Order:
  • Computed Tomography (CT) of the head to rule out space-occupying lesions or hemorrhage before proceeding with lumbar puncture if there are concerns about increased intracranial pressure.
• Treatment (Tx) with Dosages and Length:
  • Empiric antibiotic therapy for suspected bacterial meningitis (e.g., ceftriaxone 2g IV q12h) until culture results are available.
  • Antiviral therapy for viral meningitis or encephalitis (e.g., acyclovir 10mg/kg IV q8h) if herpes simplex virus is suspected.
  • Supportive care for viral meningitis, including hydration, pain management, and monitoring for complications.

This template provides a structured approach to differential diagnosis, ensuring that all potential causes are considered and that critical diagnoses are not overlooked.