Progressive multifocal leukoencephalopathy and relapsing-remitting multiple sclerosis: A comparative study

Objective: To identify clinical and magnetic resonance imaging (MRI) features that distinguish progressive multifocal leukoencephalopathy (PML) from relapsing-remitting multiple sclerosis (RRMS). Design: Retrospective medical record review. Setting: Two urban teaching hospitals in Detroit, Michigan. Patients: Forty-five confirmed PML cases and 100 patients with RRMS. Main Outcome Measures: Clinical and MRI features distinguishing PML from RRMS. Results: Overall, monosymptomatic presentations were more common in multiple sclerosis (MS) than PML (85% vs 47%; P<.01). However, patients with PML presented more often with hemiparesis (24% vs 5%; P=.001) and altered mentation (19% vs 0%; P<.0001), whereas brainstem (2% vs 18%; P=.007) presentations were more common in patients with RRMS. Spinal cord and optic neuritis presentations were seen in 18% and 33% of patients patients with RRMS, respectively, but not in patients with PML (P<.0001). Brain MRI scans, available in 35 (78%) PML cases, revealed 7 lesion types. Large, confluent T2-weighted lesions (74% vs 2%; P<.0001) and deep gray matter lesions (31% vs 7%; P<.001) were more frequent in patients with PML than patients with RRMS. Crescentic cerebellar lesions (23% vs 0%; P<.001) were seen only in patients with PML. Gadolinium-enhancing (23%), transcallosal (9%), and periventricular (9%) lesions were noted in patients with PML. Brain magnetization transfer ratio (MTR) was low in both PML and MS lesions. However, normal-appearing brain tissue MTR in PML was higher than normal-appearing brain tissue MTR in RRMS (44.15% vs 41.04%; P=.002), suggesting that PML may be relatively more focal than MS. Conclusions: There appear to be differences between the clinical and MRI characteristics of PML and RRMS, which may help distinguish new MS activity from PML. Magnetization transfer ratio studies may provide additional clues in improving early detection of PML in patients with preexisting MS and warrant further investigation.