Differential Diagnosis for Lymphocytes on CSF, Elevated C4a, Normal C3a, and Mildly Increased Polyclonal Gamma Globulins

Single Most Likely Diagnosis

• Multiple Sclerosis (MS): This condition is characterized by an increase in lymphocytes in the cerebrospinal fluid (CSF), which indicates an inflammatory process within the central nervous system (CNS). The elevated C4a level suggests activation of the classical complement pathway, which can be seen in autoimmune diseases like MS. The normal C3a level and mildly increased polyclonal gamma globulins further support this diagnosis, as MS can involve the production of various autoantibodies.

Other Likely Diagnoses

• Neurosyphilis: This condition can present with lymphocytic pleocytosis in the CSF and can involve the production of various antibodies, potentially leading to an increase in polyclonal gamma globulins. The elevated C4a could be indicative of an immune response to the infection.
• Lymphomatous Meningitis: Although less common, this condition involves the infiltration of lymphoma cells into the CNS, leading to lymphocytosis in the CSF. The immune response to the lymphoma could result in elevated complement levels and increased gamma globulins.
• Chronic Meningitis (e.g., Tuberculous Meningitis): Chronic infections can cause a lymphocytic response in the CSF, along with changes in complement levels and gamma globulins due to the ongoing immune response.

Do Not Miss Diagnoses

• Subarachnoid Hemorrhage: Although the presentation might not directly suggest a hemorrhage, the possibility of a traumatic tap or a very small, undetected hemorrhage could lead to changes in CSF composition. It's crucial to rule out this condition due to its severe implications.
• Central Nervous System Vasculitis: This rare condition involves inflammation of the blood vessels within the CNS and can present with a variety of symptoms, including changes in CSF. Missing this diagnosis could lead to severe consequences, including stroke or death.

Rare Diagnoses

• Sjögren's Syndrome with CNS Involvement: This autoimmune disorder primarily affects the exocrine glands but can have CNS manifestations, including lymphocytic pleocytosis in the CSF.
• Behçet's Disease with CNS Involvement: A form of vasculitis that can affect the CNS, leading to a variety of neurological symptoms and potential changes in CSF composition.
• CNS Sarcoidosis: A condition where sarcoidosis, a disease characterized by the formation of granulomas in various parts of the body, affects the CNS, potentially leading to lymphocytosis and other changes in the CSF.