Neuromodulation & Rehabilitation Technology for PLS

Neuromodulation — the use of electrical or magnetic fields to alter how neurons function — and advanced rehabilitation technology represent a category of investigational approaches that is particularly relevant to PLS. Unlike most drug therapies, which are designed primarily for ALS and may not address upper motor neuron pathology, neuromodulation targets the motor cortex and corticospinal tract directly. This is precisely where PLS exerts its effects. The evidence is still developing, but this is the area of investigational treatment with the strongest theoretical alignment to PLS biology.

Why neuromodulation matters for PLS specifically

PLS is a disease of the upper motor neuron system — the motor cortex, the corticospinal tracts that carry signals from brain to spinal cord, and the corticobulbar tracts that control speech and swallowing. The defining symptoms of PLS (spasticity, slowness of movement, hyperreflexia, dysarthria) all reflect dysfunction in this specific neural pathway.

Neuromodulation techniques — including transcranial direct current stimulation (tDCS) and repetitive transcranial magnetic stimulation (rTMS) — act directly on the motor cortex. They can change cortical excitability, alter the balance between excitatory and inhibitory signalling, and modify corticospinal tract function. In principle, a technique that can reduce abnormal cortical hyperexcitability (a documented feature of both ALS and PLS) could reduce spasticity and potentially slow dysfunction in upper motor neuron circuits.

This is why neuromodulation research in ALS — even studies not conducted in PLS patients — is potentially the most directly relevant investigational approach for PLS. The target system is the same.

Transcranial direct current stimulation (tDCS)

Evidence level: Emerging (for ALS); Theoretical (specifically for PLS)

Transcranial direct current stimulation applies a weak, continuous electrical current to the scalp via electrodes, modulating the resting membrane potential of neurons in the underlying cortex. Anodal stimulation (positive current) typically increases cortical excitability; cathodal stimulation (negative current) typically reduces it. In MND, where motor cortical hyperexcitability is a documented problem, the therapeutic rationale is to use cathodal or cathodal-dominant protocols to reduce abnormal excitability.

The most rigorous evidence comes from a randomized, double-blind, sham-controlled trial by Benussi et al. (2023), which evaluated cortico-spinal tDCS in 31 ALS patients. The protocol combined anodal stimulation of the bilateral motor cortex with cathodal stimulation over the spine — a combined cortico-spinal approach — delivered five days per week over two weeks, with follow-up extended to 48 weeks. The trial measured short interval intracortical inhibition (SICI) via TMS as a physiological marker of cortical inhibitory function. The results showed that active tDCS improved cortical inhibition measures compared to sham, and the open-label extension suggested functional benefits that persisted over time.

This is a well-designed study, but 31 participants is small, and the primary endpoints were physiological rather than functional. The evidence is emerging, not strong. No controlled tDCS trial has been conducted specifically in PLS patients.

What makes tDCS interesting for PLS is the accessibility of the technique. Unlike some neuromodulation approaches that require specialist equipment or implantation, tDCS devices can be operated by trained therapists in outpatient settings. Home-based tDCS is also under investigation in other neurological conditions, though a certified clinical protocol would be needed for any MND application. If controlled evidence accumulates, tDCS could be a relatively accessible adjunct to standard rehabilitation for PLS patients — but that evidence does not yet exist in PLS.

Robot-aided gait training — The Lokomat evidence in PLS

Evidence level: Limited (one PLS case report)

Robot-aided gait training uses an exoskeleton device to guide the patient through precise walking movements, providing body weight support and allowing repetitive high-intensity gait training that would be impossible to perform manually by a therapist. The most widely studied system is the Lokomat (Hocoma), which suspends the patient above a treadmill in an exoskeleton that drives leg movements in a physiologically accurate pattern.

The theoretical rationale for robot-aided gait training in upper motor neuron disease is neuroplasticity: repetitive, task-specific movement stimulation can reinforce and potentially strengthen the corticospinal pathways that control walking. In conditions where upper motor neuron circuits are progressively deteriorating, intensive gait training may help maintain those circuits' function for longer than passive exercise or conventional physical therapy.

In 2021, a case report published in Innovations in Clinical Neuroscience described a PLS patient treated with Lokomat-Pro robot-aided gait training combined with conventional physical therapy. The patient showed improvements in spasticity measures, walking ability, and balance over the course of treatment. This is a single case — the weakest form of clinical evidence — but it is the only published report of robot-aided gait training specifically in PLS, and the results were clinically meaningful for the individual patient.

Robot-aided gait training is also used in other upper motor neuron conditions — multiple sclerosis and stroke rehabilitation in particular — where evidence for spasticity reduction and gait improvement is more robust. The ALS and PLS field lacks the volume of trials that MS research has accumulated, but the biological rationale is similar: repetitive UMN-targeted movement therapy in an upper motor neuron disease.

Lokomat training requires access to a specialist rehabilitation centre with the equipment. Sessions are typically 45–60 minutes, and treatment courses range from a few weeks to several months. If you are interested in exploring this, your physical therapist or neurologist can advise whether facilities with robotic gait training capability are available in your area.

Repetitive transcranial magnetic stimulation (rTMS)

Evidence level: Limited (ALS studies only; no PLS data)

Repetitive transcranial magnetic stimulation uses brief, rapidly changing magnetic fields to induce electrical currents in the motor cortex, modulating neuronal excitability. Unlike tDCS, which uses continuous low-level current, rTMS delivers discrete pulses that can produce more powerful and longer-lasting changes in cortical excitability. The direction of effect depends on stimulation frequency: low-frequency rTMS (typically 1 Hz) tends to inhibit cortical excitability; high-frequency rTMS (10 Hz or above) tends to facilitate it. For conditions involving cortical hyperexcitability, low-frequency inhibitory protocols are the most relevant.

rTMS has been studied in ALS in several small trials, with mixed results. Some studies have shown short-term improvements in cortical inhibition measures and modest functional benefits; others have shown no significant effect. The evidence base is not sufficient to establish rTMS as an effective treatment for ALS, and there are no published controlled rTMS trials in PLS specifically.

rTMS is widely available through academic medical centres and specialist neurological services (it has established approval for treatment-resistant depression and is used clinically in various neurological conditions). The equipment and training required make it primarily a clinic-based approach. Research interest in rTMS for MND is ongoing, and future trials combining rTMS with rehabilitation or drug therapy are under consideration. This is an area to watch.

Functional electrical stimulation (FES)

Evidence level: Limited (general UMN conditions; no specific MND trials)

Functional electrical stimulation uses low-level electrical pulses applied to peripheral nerves or muscles to produce coordinated muscle contractions that assist or substitute for impaired voluntary movement. In upper motor neuron conditions, FES can be used during gait training (FES cycling, FES-assisted walking) to activate weakened or spastic muscles in more normal movement patterns.

FES has well-established evidence in stroke rehabilitation and is also used in multiple sclerosis, spinal cord injury, and other upper motor neuron conditions. The evidence base in ALS specifically is limited — most ALS FES literature focuses on respiratory FES (diaphragm pacing) rather than limb applications. In PLS, where limb spasticity is the dominant problem and respiratory function is generally preserved, limb FES during exercise has theoretical appeal, but controlled trial evidence is lacking.

Some physiotherapists working with PLS patients incorporate FES-assisted cycling or FES-augmented gait training as part of their rehabilitation programs, extrapolating from the evidence in other UMN conditions. If you are working with a physiotherapist experienced in neurological rehabilitation, this is worth discussing.

Aquatic therapy

Evidence level: Anecdotal to Limited (general UMN conditions; no controlled PLS trials)

Aquatic therapy — exercise performed in warm water — is valued by many PLS patients and their physiotherapists for its effects on spasticity. Warm water reduces muscle tone by relaxing the muscle spindle system, making movement easier and stretching more effective than on land. The buoyancy of water reduces the effective weight load on joints and muscles, enabling movements that would be difficult or impossible on land in the presence of severe spasticity.

There are no controlled trials of aquatic therapy in PLS specifically, and the evidence in ALS is very limited. The rationale is strongly extrapolated from evidence in multiple sclerosis (where aquatic therapy has a modest evidence base for spasticity and fatigue) and from general upper motor neuron rehabilitation principles.

In practice, aquatic therapy is widely used by PLS patients who have access to it, and clinical experience is generally positive. The key practical considerations are safety (adequate supervision, appropriate water temperature, monitoring for fatigue and overheating), and access (not all rehabilitation facilities have hydrotherapy pools). This is a reasonable component of a comprehensive physiotherapy program and is mentioned on the current treatments page as a practical option.

Putting this together