Dr. Scott of Allegheny Neurological Associates received payments from Biogen, Genentech, Genzyme, and Novartis for advisory work, consulting, and speaking engagements and research support from Biogen and Genentech.)
Dr. Reder of the University of Chicago received honorariums from Bayer, Biogen Idec, Caremark Rx, Genentech, Genzyme, Novartis, Mallinckrodt, Mylan, Serono, and Teva-Marion for service on advisory boards and as a consultant as well as stock options from NKMax America for advisory work.)
This article includes discussion of Balo concentric sclerosis, leukoencephalitis periaxialis, Schilder encephalitis periaxialis diffusa, Marburg encephalitis, and concentric sclerosis. The foregoing terms may include synonyms, similar disorders, variations in usage, and abbreviations.
Balo concentric sclerosis is often thought of as a distinct demyelinating syndrome. The author argues that no absolute evidence differentiates Balo concentric sclerosis from other acute, aggressive forms of multiple sclerosis, although there are many indications that a district pathology may become clear in the future. The article discusses how the spectrum of Balo concentric sclerosis has changed with the discovery of nonfatal cases by MRI. In addition, it describes its spectrum of symptoms and provides the current concepts behind the formation of its rings. The author speculates that much about the mechanism of tissue destruction in multiple sclerosis may be inferred from pathological observations in Balo concentric sclerosis. This update includes the most recent descriptions of MRI findings, comparing Balo concentric sclerosis to prototypic multiple sclerosis.
• Balo concentric sclerosis shares features with other forms of acute demyelination, including multiple sclerosis, neuromyelitis optical, and myelin oligodendrocyte glycoprotein–associated demyelinating disease.
• Many cases with a Balo concentric sclerosis pattern noted by magnetic resonance imaging do not progress to multiple sclerosis and have a limited course.
• The concentric ring pattern of Balo concentric sclerosis may be explained by activated microglia and macrophages migrating centrifugally and concentrating in rings for which spacing and activation state is determined by an inhomogeneous diffusion of chemokines and cytokines.
• Activated microglia and macrophages release nitric oxide and oxygen radicals, which may inhibit complex IV of cytochrome c oxidase, leading to failure of energy production and cell death. This might be a hyperacute form of a pathology often associated with multiple sclerosis.
Historical note and terminology
Balo concentric sclerosis is a CNS disease with characteristic pathological and MRI features consisting of alternating concentric rings of demyelinated and relatively myelinated tissues. The evidence that the MRI pattern is tantamount to Balo concentric sclerosis by pathological criteria is based on biopsied cases. The unusual and puzzling pattern has led to a distinctive place in multiple sclerosis nosology following its description by Balό (Balo 1927). When Balό gave this rare pattern the name “leukoencephalitis periaxialis concentrica,” it became inevitable that future neurologists would link his name to the entity. Nonetheless, the first description of this pathological pattern should be attributed to Marburg who wrote about it 21 years earlier as part of the spectrum of changes found in acute multiple sclerosis (Marburg 1906).
Currently, whether or not Balo concentric sclerosis is a distinct entity is somewhat controversial. A few reviewers have lumped Balo leukoencephalitis periaxialis, Schilder encephalitis periaxialis diffusa, and Marburg encephalitis periaxialis scleroticans under the single term “concentric sclerosis” (Courville 1970). The distinction between Balo concentric sclerosis, tumefactive multiple sclerosis, and prototypic multiple sclerosis has been described as overlapping syndromes (Hardy et al 2016). Because about half of the published cases occur in the setting of typical multiple sclerosis (Kastrup et al 2002), Balo concentric sclerosis has frequently been thought to be a variant of multiple sclerosis. Because a significant number of patients with Balo concentric sclerosis lesions have severe and disabling attacks, this view suggests that Balo concentric sclerosis occurs when unfavorable pathological factors are found in a small portion of patients, many of whom progress to multiple sclerosis. Importantly, not all patients with a Balo-like presentation subsequently develop multiple sclerosis.
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