Expanding the neurological spectrum of HTLV-1 beyond HAM/TSP: a contemporary perspective

Human T-lymphotropic virus type 1 (HTLV-1) has long been linked mainly to HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). However, four decades of research show that the virus causes a much broader range of neurological conditions. In Latin America and the Caribbean-regions with high prevalence but limited awareness, diagnostic capacity, and treatment-its burden is especially severe. Misdiagnosis or neglect often delays care, leading to increased disability and emotional distress. This Personal View highlights the expanding neurological spectrum of HTLV-1, which includes rare but well-documented encephalopathy, cognitive decline, peripheral neuropathy, inflammatory myopathy, cerebellar dysfunction, autonomic disorders, motor neuron disease-like syndromes, and seizures. These can happen independently or alongside HAM/TSP. The proposed concept of an "HTLV-1 neurological complex" better represents this multifaceted involvement. Recognising this diversity is essential for accurate diagnosis and better outcomes, particularly in endemic settings. A paradigm shift is needed-one that broadens the clinical focus beyond myelopathy to encompass the full neurological spectrum, thereby improving global care and management.