Introduction Neurosarcoidosis is a great mimicker and distinction from multiple sclerosis can be troublesome. This study characterises a cohort of neurosarcoidosis patients with focus on CSF analysis and whether this could help distinguish these two conditions.

Methods We enrolled 80 patients with a diagnosis of neurosarcoidosis based on stringent diagnostic criteria. The CSF and serum oligoclonal IgG patterns after iso-electric focusing were compared.

Results 80 patients had a probable or definitive diagnosis of neurosarcoidosis. MRI findings were leptomeningeal enhancement (35%) and white matter and spinal cord involvement (30% and 23%). PET was positive in (62%) of isolated neurosarcoidosis. CSF analysis showed that oligoclonal bands were rare (3% had CSF alone,11% with mirror pattern). No patient with definite neurosarcoidosis had CSF oligoclonal bands. Only 14% of patients with definite neurosarcoidosis had elevated serum ACE, CSF ACE was absent in all.

Discussion Large elevations in CSF protein, WCC and ACE occur in neurosarcoidosis, but are rare in MS. However, minimal changes may occur in both conditions. Intrathecal oligoclonal IgG is a powerful discriminator as it is rare in neurosarcoidosis but common in MS (95–98%). We suggest caution in making a diagnosis of neurosarcoidosis when intrathecal oligoclonal IgG synthesis is found.