Differential Diagnosis for Altered Mental Status

The patient's presentation of altered mental status, cough, headache, vomiting, and history of intravenous drug use, along with the cerebrospinal fluid (CSF) findings, suggests a central nervous system (CNS) infection. The key CSF findings include elevated protein, low glucose, and a white blood cell (WBC) count with lymphocyte predominance.

• Single Most Likely Diagnosis

  • Cryptococcus neoformans: This is a common cause of meningitis in immunocompromised patients, particularly those with a history of intravenous drug use. The CSF profile (elevated protein, low glucose, and lymphocytic pleocytosis) is consistent with cryptococcal meningitis. Cryptococcus neoformans is notorious for causing severe CNS infections in individuals with compromised immune systems.

• Other Likely Diagnoses

  • Tuberculosis: Tuberculous meningitis can present with similar CSF findings, including elevated protein, low glucose, and a lymphocytic predominance. A history of cough and headache could also suggest pulmonary tuberculosis, which increases the likelihood of CNS involvement.
  • Cytomegalovirus: CMV can cause CNS infections, including meningitis and encephalitis, particularly in immunocompromised individuals. However, the presentation might be more varied, and diagnosis often requires specific testing like PCR.

• Do Not Miss Diagnoses

  • Toxoplasma gondii: Although less likely given the CSF findings, toxoplasmosis is a critical diagnosis to consider in immunocompromised patients, as it can cause life-threatening CNS infections. It's often associated with ring-enhancing lesions on CT or MRI, but these might not always be present.
  • Primary CNS Lymphoma: This condition can mimic infectious processes and is a consideration in immunocompromised patients presenting with CNS symptoms. However, the diagnosis typically requires imaging findings suggestive of lymphoma and/or biopsy.

• Rare Diagnoses

  • Other rare fungal infections or unusual bacterial pathogens could potentially present similarly but are less likely given the information provided. These might include infections like histoplasmosis or coccidioidomycosis, depending on the patient's geographic history and other risk factors.