Low signal intensity in U-fiber identified by susceptibility-weighted imaging in two cases of progressive multifocal leukoencephalopathy

• This report describes two PML cases showing characteristic findings on SWI.
• This is the first report of a new finding of SWI in PML.
• SWI showed low signal intensities in U-fibers, progressing with disease progression.
• This finding may be useful for the diagnosis of PML.

Magnetic resonance imaging (MRI) is a useful tool for diagnosing and monitoring progressive multifocal leukoencephalopathy (PML). Although characteristic MRI findings of PML are well known, we noted a potential new finding for this disease on susceptibility-weighted imaging (SWI). Two patients with PML were studied and followed using MRI. SWI revealed low signal intensities in U-fibers adjacent to the white matter lesions of PML. These findings progressed along with the disease progression. The cause underlying these findings remains unclear. This new finding suggests that SWI is useful for the diagnosis of PML. It can provide a helpful clue in a clinical setting.