Differential Diagnosis

• Single most likely diagnosis
  • Cryptococcal meningitis: This diagnosis is likely due to the patient's history of intravenous drug use, which increases the risk of immunocompromised status and subsequent fungal infections. The symptoms of progressive diffuse headache, generalized malaise, low-grade fever, weight loss, neck stiffness, and cranial nerve abnormalities (such as weakness of the lateral rectus muscle and bilateral papilledema) are consistent with cryptococcal meningitis. The cerebrospinal fluid (CSF) analysis showing elevated opening pressure, low glucose, elevated protein, and lymphocytic pleocytosis further supports this diagnosis.
• Other Likely diagnoses
  • Tuberculous meningitis: This diagnosis is considered due to the patient's symptoms of chronic headache, malaise, fever, weight loss, and neck stiffness, which are similar to those of cryptococcal meningitis. The CSF analysis also shows findings consistent with tuberculous meningitis, such as low glucose and elevated protein.
  • Viral meningitis: Although less likely than fungal or tuberculous meningitis, viral meningitis could still be a consideration given the patient's symptoms and CSF analysis showing lymphocytic pleocytosis.
• Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
  • Subarachnoid hemorrhage: Although the CT scan did not show evidence of hemorrhage, it is essential to consider this diagnosis due to the patient's sudden onset of headache and neck stiffness. A repeat CT scan or lumbar puncture may be necessary to rule out this condition.
  • Meningitis due to other pathogens (e.g., bacterial, parasitic): It is crucial to consider other infectious causes of meningitis, as prompt treatment with the appropriate antimicrobial agents is essential to prevent serious complications and death.
• Rare diagnoses
  • Coccidioidal meningitis: This fungal infection is rare but can occur in immunocompromised individuals, particularly those with a history of intravenous drug use. The patient's symptoms and CSF analysis could be consistent with coccidioidal meningitis.
  • Histoplasmosis: This fungal infection can cause meningitis, particularly in immunocompromised individuals. Although rare, it should be considered in the differential diagnosis, especially if the patient has a history of exposure to bird or bat droppings.
  • Sarcoidosis: This condition can cause neurosarcoidosis, which may present with symptoms similar to those of the patient, including headache, malaise, and cranial nerve abnormalities. However, the CSF analysis and imaging findings would likely be different from those of infectious meningitis.