Differential Diagnosis for a 30-year-old Male with Fever, Neck Stiffness, and Altered Sodium Levels

Single Most Likely Diagnosis

• Tubercular Meningitis (TBM): Given the patient's past history of pulmonary tuberculosis (TB) and current symptoms of fever, neck stiffness, and altered sensorium, TBM is a strong consideration. The lymphocytic predominance in the cerebrospinal fluid (CSF) analysis (though not fully provided) and the clinical presentation support this diagnosis.

Other Likely Diagnes

• Viral Meningitis: The presence of fever, neck stiffness, and altered sensorium could also suggest viral meningitis, especially given the lymphocytic predominance in the CSF. However, the patient's past history of TB and the severity of symptoms might lean more towards TBM.
• Chronic Meningitis: This could be due to various causes including fungal, parasitic, or other bacterial infections. The patient's symptoms of prolonged fever and neck stiffness could fit this diagnosis, but the specific cause would need further investigation.
• Central Nervous System (CNS) Tuberculoma: While the CMRI was reported as normal, CNS tuberculomas can sometimes be missed on initial imaging, especially if they are small or if the imaging quality is not optimal. The patient's past history of TB and current neurological symptoms make this a plausible diagnosis.

Do Not Miss Diagnoses

• Bacterial Meningitis: Although the patient's CSF analysis suggests a lymphocytic predominance, bacterial meningitis can present with a variety of CSF profiles, especially early in the course of the disease. It is crucial to consider and rule out bacterial meningitis due to its high morbidity and mortality if not promptly treated.
• Cryptococcal Meningitis: This is particularly important in immunocompromised patients or those with a history of TB, as it can present with similar symptoms and requires specific treatment.
• Neurosyphilis: Given the patient's presentation with neurological symptoms and fever, neurosyphilis should be considered, especially if there is a history of sexually transmitted infections.

Rare Diagnoses

• CNS Lymphoma: Although rare, CNS lymphoma can present with a variety of neurological symptoms, including fever, altered mental status, and neck stiffness. It is more common in immunocompromised patients.
• Sarcoidosis: Neurosarcoidosis can mimic many other neurological conditions, including meningitis, and should be considered in patients with unexplained neurological symptoms and a history of sarcoidosis.
• Whipple's Disease: A rare, systemic bacterial infection that can affect the CNS, presenting with a variety of symptoms including fever, altered mental status, and neurological deficits.

Each of these diagnoses requires careful consideration of the patient's clinical presentation, laboratory results, and imaging studies to guide further investigation and management.