What is the initial diagnostic test for multiple sclerosis and what finding is expected?

• A. CT head
• B. Lumbar puncture showing oligoclonal bands and elevated IgG
• C. EEG
• D. Ultrasound of the optic nerve

Answer: (B)

Multiple sclerosis is diagnosed by evidence of demyelination that is disseminated in time and space. While MRI is the primary imaging test to identify demyelinating lesions in the brain and spinal cord, a lumbar puncture with analysis of cerebrospinal fluid provides a highly characteristic laboratory finding: oligoclonal bands and an elevated IgG index. Oligoclonal bands represent intrathecal synthesis of IgG from clonally expanded B cells within the CNS and are present in the majority of MS patients. The elevated IgG index confirms that this IgG production is occurring inside the CNS rather than being derived from the bloodstream. This CSF profile strongly supports the diagnosis, especially when MRI findings are equivocal or to bolster confidence in the diagnosis. CT head is not sensitive for MS lesions, EEG is not diagnostic for MS, and ultrasound of the optic nerve does not provide a definitive MS diagnosis.