24 - White Matter and Myelin Disorders

This chapter focuses on the surgical neuropathology of demyelinating diseases of the central nervous system, that is, diseases in which myelin itself or the oligodendrocytes (or astrocytes in neuromyelitis optica) represent the targeted element with relative (although, in most cases, not absolute) preservation of axonal integrity. The chapter also includes diseases in which white matter is preferentially targeted by processes that are often more destructive than they are demyelinating (e.g., fat embolism, human immunodeficiency virus [HIV]-induced leukoencephalitis/vacuolar myelopathy). Diseases of the white matter are often neglected in surgical neuropathology, given the greater focus on neoplastic disease that forms the majority of diagnostic biopsies. Nonetheless, an important part of surgical neuropathology is the recognition of neoplasia in the presence of reactive myelinopathy and the need to avoid traps in the false recognition of reactive tumorous myelinopathic processes as neoplasm ("tumefactive multiple sclerosis"). Neuroradiologic techniques are more capable of localizing processes to permit stereotactic biopsies and increase the variety of diseases discussed in this chapter, diseases which would not have been previously considered for biopsy and were only confirmed at autopsy. Molecular genetic analysis now contributes substantively to the workup of white matter disease, particularly leukodystrophies. Thus, in this chapter there are discussions of common demyelinating disorders (multiple sclerosis, acute disseminated encephalomyelitis), destructive leukoencephalopathy, and leukoencephalitis, as well as rare forms of hereditary leukodystrophies, which are, admittedly, infrequently encountered in surgical biopsies.