Background,  The etiology of multiple sclerosis is unclear and infectious agents have been considered. Borrelia infections can cause an intrathecal inflammatory response with accompanying cerebral and spinal imaging findings.

Cases. Two children with acute or subacute initial neurological presentation, subsequent relapsing  course, and MR imaging features suggestive of multiple sclerosis are presented. A history of tick bite or dramatic response to antibiotic treatment supported Lyme disease in the beginning, but requirement of disaese-modifying treatment later in the course supported multiple sclerosis.

Results. These cases carrying features supportive of both multiple sclerosis and Lyme disease caused clinical dilemma and were treated for both disorders. Borrelia-specific IgG index testing before any treatment could have prevented the difficulty in differential diagnosis.

Conclusions. Clinical, imaging and CSF findings of multiple sclerosis and acute or chronic progressive borrelia encephalomyelitis may overlap and testing for Borrelia-specific intrathecal antibody synthesis should not be omitted in endemic areas.