Neuromodulation to Enhance Motor Function in HSP

Hereditary spastic paraplegia (HSP) is a rare neurological condition that causes stiffness, weakness, and difficulty walking due to damage in the nerves that control movement. This study will test whether a noninvasive form of spinal cord stimulation, called transcutaneous spinal cord stimulation (tSCS), can improve walking and reduce muscle stiffness in adults with HSP. In this study, participants will receive tSCS twice a week for 8 weeks. The stimulation is delivered through self-adhesive electrodes placed on the skin over the lower back and does not require surgery. Each session will last about one hour. After the treatment period, participants will be followed for an additional 8 weeks without stimulation to see whether any improvements are maintained. Researchers will measure walking speed, walking endurance, muscle stiffness, and overall disease severity. Additional tests will explore changes in bladder and bowel function and muscle strength.

Inclusion Criteria: * Clinical diagnosis of hereditary spastic paraplegia (genetic confirmation if available). * Stable medications for spasticity and other neurologic symptoms for =4 weeks prior to enrollment. * Able to participate in study visits and assessments with or without assistive devices. * If ambulatory: able to walk at least 10 meters with or without an assistive device. * If wheelchair user: able to perform seated mobility tasks and transfers required for assessments. * Capacity to provide informed consent and follow study procedures, with an ability to communicate and understand instructions in English Exclusion Criteria: * Implanted electronic devices (e.g., pacemaker, deep brain stimulator, intrathecal pumps). * Severe cardiopulmonary disease that would make participation unsafe. * Open skin lesions or severe dermatologic conditions at electrode sites. * Pregnancy or plans to become pregnant during the intervention period. * Diagnosed with Primary Lateral Sclerosis (PLS) or another neurological condition that affects walking, such as stroke, multiple sclerosis (MS), or a recent surgery on legs. * Unable to participate in basic movement or mobility assessments, even with their usual mobility device (such as a wheelchair, walker, or cane). People who use wheelchairs or other mobility aids can participate if they can complete the study's mobility assessments in their usual way. * Cognitive or psychiatric conditions that make it difficult to give informed consent or follow study instructions. * Diagnosed with Urinary Tract Infection (UTI), either acute or ongoing, before or at the time of study enrollment. * Diagnosed with epilepsy. * Participation in another interventional clinical trial that could affect mobility or spasticity during the study. * A recent change (within the last 4 weeks) in medications or treatments that affect spasticity or movement (for example: baclofen, tizanidine, botulinum toxin injections). * Expect to start or change treatments for spasticity or mobility during the study period. * Any condition judged by the investigator to pose excess risk or confound outcomes.