Understanding progressive multifocal leukoencephalopathy: links between milky-way appearance and mismatch T2/FLAIR

Area of Science:

• Neurology
• Radiology
• Infectious Diseases

Background:

• Magnetic resonance imaging (MRI) is crucial for diagnosing progressive multifocal leukoencephalopathy (PML).
• Understanding the radiological spectrum, lesion evolution, and anatomical predilection in PML is limited.
• New insights into PML pathophysiology and early radiological markers are emerging from recent studies.

Purpose of the Study:

• To introduce the T2/fluid-attenuated inversion recovery (FLAIR) mismatch sign as a marker for cavitated PML lesions.
• To explore the relationship between the T2/FLAIR mismatch sign and the milky-way appearance, an early PML sign.
• To hypothesize about viral dissemination routes in PML.

Main Methods:

• Retrospective longitudinal study of 13 progressive multifocal leukoencephalopathy patients.
• Analysis of clinical and MRI features from January 2010 to January 2020.
• Focus on patients at the symptomatic stage of the disease.

Main Results:

• HIV was the most prevalent underlying pathology (61.5%).
• Motor deficit was the most common symptom (76.9%).
• Frontal lobes, middle cerebellar peduncle, cerebellum, and pons were frequently affected.
• Milky-way appearance was observed in 58.3% of patients.
• T2/FLAIR mismatch was found in 5 patients with milky-way appearance (P=0.02).
• T2/FLAIR mismatch demonstrated high sensitivity and specificity (100-71%) for evolved lesions.

Conclusions:

• Tract-dependent spread, clinical, and genetic factors influence MRI variability in PML.
• The milky-way appearance may indicate a transitional phase to evolved lesions.
• T2/FLAIR mismatch is a key MRI sign for diagnosing evolved PML lesions.
• Both milky-way appearance and T2/FLAIR mismatch are valuable for diagnosing symptomatic PML.