Coincidental Coexistence of Human T-lymphotropic Virus Type 1 (HTLV-1)-Associated Myelopathy/Tropical Spastic Paraparesis and Myasthenia Gravis in a Patient With Chronic HTLV-1 Infection: A Case Report

Abstract

Human T-lymphotropic virus type 1 (HTLV-1) infection profoundly alters central immune regulation via molecular mechanisms involving the viral proteins transactivator X and HTLV-1 basic leucine zipper factor, which promote the proliferation of autoreactive T lymphocytes and the dysfunction of regulatory T cells, resulting in persistent inflammation of the central nervous system. These alterations not only explain the occurrence of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) but have also been associated with the development of autoimmune diseases such as myasthenia gravis (MG). While the connection between chronic HTLV-1 infection and MG is still anecdotal, a small number of case studies and limited molecular research suggest a potential link. Recent investigations have identified HTLV-1 tax and pol gene sequences in thymic tissue from MG patients, supporting the idea that the virus can persistently infect the thymus and interfere with the negative selection of T lymphocytes. Here, we present the case of a patient with HAM/TSP for over 12 years who subsequently experienced a myasthenic crisis, confirmed by the detection of anti-acetylcholine receptor autoantibodies. The patient responded favorably to treatment with acetylcholinesterase inhibitors. The absence of thymoma, together with a history of chronic retroviral infection, reinforced the potential role of HTLV-1 as a trigger for autoimmunity in the absence of structural abnormalities. This case illustrates the clinical and molecular convergence between retroviral infection and immune dysfunction, providing further support for a model of virally induced autoimmunity.

Keywords: antibody-mediated disease; htlv-1; human t-lymphotropic virus; myasthenia gravis; neuroinflammation; neurologic complications; neuromuscular autoimmune disease; rare case report; retroviral infection; tropical spastic paraparesis.

Figure 1. T1-weighted sagittal MRI scan of the cervical spine.

Preserved cervical spinal cord with no compressive lesions, intramedullary signal alterations, or significant atrophy. The upper arrow indicates the mid-cervical cord, where spinal morphology and signal are preserved. The lower arrow shows an intervertebral space with no disc protrusion or canal stenosis. No overt signs of cervical myelopathy are visible on this sequence. Thoracic spine imaging was not available for evaluation of spinal cord atrophy often associated with human T-lymphotropic virus type 1-associated myelopathy/tropical spastic paraparesis.