Ultrastructural pathology of a Chilean case of tropical spastic paraparesis human T-cell lymphotropic type I-associated myelopathy (TSP/HAM)

Human T-cell lymphotropic virus type I (HTLV-I), is the cause of endemic tr opical spastic paraparesis (TSP) or HTLV-I-associated myelopathy (HAM). Bec ause TSP/HAM is not a fatal disease, the neuropathology of this disease, al beit relatively well understood, is based on the examination of just a few incidental cases. Previously, we demonstrated peculiar lamellated structure s, called "multilamellar bodies" (MLB). In this report, we present the ultr astructural neuropathology of a TSP/HAM case from Chile, with further detai led descriptions of MLB. It is tempting to suggest that MLB may represent s pecific ultrastructural markers of TSP/HAM. The pathology of the anterior a nd posterior horns was similar and was comprised of axonal degeneration, ac companied by extensive astrocytic gliosis. Lymphocytic infiltration, partic ularly observed as "cuffs" around blood vessels, was scattered among Other cellular elements. Ultrastructurally, myelin sheaths were relatively well p reserved, and some demyelinated but not remyelinated fibers were observed. Moreover, axons with abnormal accumulations of neurofilaments, suggestive o f axonal degeneration, were detected. Several axons contained Hirano bodies . In many samples, glial processes replaced most of the remaining neuropil. In a few specimens of the anterior and posterior horns of the spinal cord, MLB were observed. These structures consisted of stacks of 30 to 40 electro n-dense lamellae, which were interrupted by narrow electron-lucent spaces. All of the lamellae were immersed within an amorphous substance of intermed iate density. Neurons of the dorsal root ganglia were basically normal except for increas ed lipofuscin accumulation. As in the spinal cord, myelinated axons were we ll preserved, but a few were demyelinated and surrounded by concentric arra ys of Schwann cell membranes. Also, axons of the dorsal roots accumulated i ncreased number of neurofilaments. Mast cells and Schwann cells were increa sed in number, the latter containing abundant pi granules and myelin fragme nts.