“String of Pearls” Sign in Progressive Multifocal Leukoencephalopathy — A Radiologic Hallmark Beyond Susac’s Syndrome
Busranur Agac1, Govind Bhagavatheeshwaran1, Serhat V. Okar1, Yair Mina1, Daniel Reich1, Irene Cortese1
1National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH)
Background:
"String of pearls" sign is a radiologic hallmark for Susac’s syndrome representing microinfarcts along the internal capsules due to autoimmune vasculitis.
Results:
A 64-year-old woman with history of rheumatoid arthritis and immunosuppressive medication use presented with dysarthria, right-sided ataxia, and gait imbalance. Her brain MRI showed T2-weighted fluid-attenuated inversion recovery (T2-FLAIR) hyperintensities involving the right cerebellum and pons. Her cerebrospinal fluid (CSF) analysis showed positive JCV PCR confirming the diagnosis of progressive multifocal leukoencephalopathy (PML). PML continued to progress despite experimental immunotherapy. Her follow-up MRI 6 months after the diagnosis showed punctate hyperintense lesions on diffusion-weighted imaging (DWI) that appeared isointense on apparent diffusion coefficient (ADC) and T2-FLAIR hyperintensities associated with hypointense signal on T1-weighted images extending from the brainstem to the internal capsules along the corticospinal tracts as well as in bilateral posterior limbs of the internal capsules in "string of pearls" appearance on axial slices.
Conclusions:
Although "string of pearls" sign is classically associated with Susac’s syndrome, representing microinfarcts in the internal capsules, we describe its appearance in progressive multifocal leukoencephalopathy as a result of lesion extension along the corticospinal tracts.
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