Hypoxia-like tissue injury and glial response contribute to Balo concentric lesion development

OBJECTIVE To clarify the pathogenic factors and mechanisms underlying the development of concentric demyelinating lesions in Balo disease. METHODS We conducted serial clinical, MRI, and histopathologic assessments of concentric lesion formation in a case of relapsing Balo disease. RESULTS The patient experienced 2 attacks caused by left parietal and left frontal lesions in 5 years. In MRI findings from both episodes of expanding lesions, there were diffusion-restricted rings that antedated the appearance of gadolinium enhancement; subsequently, typical concentric T2 lesions appeared concurrently with the disappearance of this enhancement. Histopathologic examinations of biopsied brain tissues revealed definite concentric demyelinating layers typical of Balo disease with massive macrophage infiltration but preserved axons. Numerous hypertrophic astrocytes were observed beyond the edges of and within the demyelinating layers. The expression of hypoxia-inducible factor-1α, a protein related to hypoxia-induced tissue preconditioning that contributes to survival and protection against further hypoxia-like injury, was upregulated primarily in glial cells located beyond the edge of the demyelinating layers but was also elevated in hypertrophic astrocytes on the inner sides of resected lesions and in oligodendrocytes in nondemyelinating layers. In addition, these astrocytes expressed CC motif chemokine 2 and/or interleukin-1β, which are inducible by hypoxia-inducible factor-1α and potentially promote demyelination. CONCLUSIONS Our study suggests that a unique interplay between hypoxia-induced tissue preconditioning and proinflammatory cytokines derived from glial cells may contribute to the development of concentric demyelinating lesions in Balo disease.