Differential Diagnosis for the 29-year-old Woman

The patient presents with symptoms of severe headache, stiff neck, vomiting, fatigue, photophobia, and fever, along with specific cerebrospinal fluid (CSF) findings. Based on these, the differential diagnoses can be categorized as follows:

• Single Most Likely Diagnosis

  • Viral Meningitis: The CSF findings of a hazy appearance, elevated white blood cell count (WBC) with a predominance of lymphocytes (80%), and the presence of fever and symptoms like headache, stiff neck, and photophobia are highly suggestive of viral meningitis. The lymphocytic predominance is a key indicator of viral etiology.

• Other Likely Diagnoses

  • Bacterial Meningitis (early stage): Although the CSF differential shows a lymphocytic predominance, which is more typical of viral meningitis, early in the course of bacterial meningitis, the CSF may show a mixed picture before neutrophils become predominant. The presence of fever, headache, stiff neck, and a hazy CSF appearance could still suggest bacterial meningitis, especially if the patient is seen early in the disease process.
  • Tuberculous Meningitis: This condition can present with similar symptoms, including headache, fever, and stiff neck. The CSF typically shows a high lymphocyte count, which aligns with the patient's CSF findings. However, tuberculous meningitis often has a more subacute presentation and may be associated with other systemic symptoms or risk factors for tuberculosis.

• Do Not Miss Diagnoses

  • Subarachnoid Hemorrhage: Although the CSF RBC count is relatively low (10/μL), any presence of RBCs in the CSF should prompt consideration of subarachnoid hemorrhage, especially given the patient's severe headache. This condition is a medical emergency and requires immediate diagnosis and treatment.
  • Herpes Simplex Encephalitis: This condition can present with fever, headache, and altered mental status. While the CSF findings may overlap with viral meningitis, herpes simplex encephalitis is a medical emergency that requires prompt antiviral treatment to prevent significant morbidity and mortality.

• Rare Diagnoses

  • Fungal Meningitis: This condition is more common in immunocompromised patients but can present with similar symptoms to viral or bacterial meningitis. The CSF findings may show a lymphocytic predominance, but the diagnosis is often made based on culture or molecular testing.
  • Sarcoidosis-related Meningitis: Sarcoidosis can involve the central nervous system and present with meningitis symptoms. The CSF typically shows a lymphocytic pleocytosis, and the diagnosis is often suggested by other systemic manifestations of sarcoidosis or by specific testing.