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Pathology of chronic myelopathy associated with HTLV-I infection (HAM/TSP)
1Department of Neurological Sciences, Tohoku University School of Medicine, Sendai, Japan.
Insights
Japanese patients with HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) exhibit chronic spinal cord inflammation and white matter degeneration. These findings support classifying HAM/TSP as chronic progressive parainfectious myelitis.
Area of Science:
- Neuropathology
- Infectious Diseases
Background:
- Human T-lymphotropic virus type I (HTLV-I) infection is linked to neurological disorders.
- HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP) is a chronic inflammatory myelopathy.
Purpose of the Study:
- To review the central nervous system (CNS) pathology in Japanese HAM/TSP autopsy cases.
- To characterize the histopathological features and compare them with findings in other regions.
Main Methods:
- Review of 10 autopsy cases of Japanese HAM/TSP patients with confirmed HTLV-I infection.
- Histopathological examination of spinal cord tissue, focusing on inflammation and white matter degeneration.
Main Results:
- Consistent findings of chronic progressive inflammation with lymphocyte and monocyte exudation in grey and white matter.
- Severe white matter degeneration, most prominent in the lower thoracic cord, particularly affecting the lateral columns and pyramidal tracts.
- Histopathological features largely consistent with HAM/TSP in tropical regions, despite absent detectable HTLV-I antigens at inflammatory sites.
Conclusions:
- The observed pathology aligns with a chronic progressive parainfectious myelitis.
- The findings support the classification of HAM/TSP as a distinct clinicopathological entity.
- Understanding the CNS pathology is crucial for diagnosing and managing HTLV-I-associated neurological complications.
Abstract:
The CNS pathology of 10 autopsy cases of Japanese HAM/TSP patients with a serological confirmation of HTLV-I infection was reviewed. The essential histopathological feature was a chronic progressive inflammatory process with marked parenchymal exudation of lymphocytes and monocytes into both the grey and white matter of the spinal cord, uniquely perpetuating for more than 3 years after the onset of neurological symptoms, and resulting in severe degeneration of the white matter accompanied by marked glio-mesenchymal tissue reactions. Both the inflammation and the white matter degeneration were most conspicuous in the lower thoracic cord. The lateral column was always and most severely affected. Although the parenchymal tissue degeneration was not confined to any particular long tracts, symmetrical degeneration of the lateral pyramidal tract was evident in all cases. Diffuse myelin pallor was also seen in the anterior column but it was usually mild. The posterior column was commonly involved but the severity and extent of the white matter degeneration were variable. Neurons were relatively well preserved. These histopathological features of HAM/TSP in Japan largely agree with those previously described for HAM/TSP in tropical regions. In the absence of detectable amount of HTLV-I antigens at the sites of inflammation, "chronic progressive parainfectious myelitis" seems to be the most appropriate descriptive term for this unique histopathology of HAM/TSP.