PLS Spasticity Research
For most people with PLS, spasticity is the disease. Not in the sense that it is the only problem — fatigue, pain, and cognitive effects are real too — but in the sense that the velocity-dependent muscle stiffness, the scissor gait, the cramping, the difficulty taking steps: these are what most PLS patients are managing every day for decades. That makes the spasticity evidence base uniquely important. And the honest truth about it is that the evidence is thinner than it should be, almost all of it extrapolated from other diseases, and the area with the most room for real breakthrough — rehabilitation — has barely been studied at all.
The hard truth about the evidence base
There has never been a randomized controlled trial of any spasticity treatment conducted specifically in a PLS population. Almost everything clinicians use to treat PLS spasticity has been tested in multiple sclerosis, spinal cord injury, or stroke — conditions with upper motor neuron-driven spasticity that resembles PLS in mechanism but differs in pathology, pace, and context. The extrapolation is reasonable; it is not established.
This is not a minor caveat. PLS spasticity is cortical in origin — the motor neurons that are degenerating live in the motor cortex, and the spasticity they generate when they fail may respond differently to drugs that work primarily on spinal interneurons. Understanding that distinction is not just academic: it directly affects which treatments to try first, at what doses, and in what sequence. The research reviewed here is the best available evidence, and it should be read in full awareness of where it comes from.
Where the evidence comes from
The most directly applicable pharmacological trial for PLS spasticity is the tizanidine versus baclofen randomized controlled trial. Conducted in 66 patients with multiple sclerosis and clinically significant spasticity, this double-blind crossover study put the two first-line oral agents head-to-head — the only such direct comparison in the literature. The findings were nuanced: neurologists and physiotherapists judged baclofen marginally superior on overall efficacy and tolerance, but the side-effect profiles diverged sharply. Baclofen caused significantly more muscle weakness. Tizanidine caused more sedation and dry mouth. For PLS patients where preserving whatever ambulatory function remains is a central goal, that weakness distinction is not minor — it informs a preference for tizanidine in patients who are still walking and want to stay that way. This trial provides the clearest signal the field has on how to choose between these agents.
When oral agents fail, intrathecal baclofen (ITB) pump implantation is the standard next step for severe refractory spasticity. The backbone of confidence in long-term ITB is a 2004 Spinal Cord study: the 40-patient long-term follow-up that tracked outcomes over years rather than weeks. The study confirmed that spasticity reduction is sustained over time, not just acutely after pump placement, and it mapped the complication landscape in clinical detail. That complication profile — catheter malfunction, pump failure, infection, and above all the risk of abrupt baclofen withdrawal — is the essential safety knowledge for any patient or family considering pump implantation. Withdrawal is potentially life-threatening: hyperthermia, escalating spasticity, rhabdomyolysis, and multi-organ failure if unrecognized. Understanding this risk before committing to a pump is not optional. The 2004 study is where that understanding is grounded.
Whether ITB works the same way when the spasticity originates in the cortex rather than the spinal cord is an important mechanistic question. PLS is a cortical disease. Most ITB evidence comes from spinal cord injury and MS — conditions with predominantly spinal-origin spasticity, where baclofen delivered near spinal interneurons acts directly on the circuit generating the tone. The 2010 comparative analysis of spinal versus cortical spasticity addressed this directly. Both groups responded to ITB, but patients with cortical-origin spasticity required higher doses and showed more variable functional gains than those with spinal-origin disease. The takeaway for PLS is practical: ITB works for cortical spasticity, but titration is more demanding and expectations need calibrating. Higher pump doses, less predictable functional outcomes, and more careful selection are all appropriate features of PLS-specific ITB management.
PLS-specific ITB evidence is thin but exists. The clinical short communication on ITB utility in PLS reported a small series of PLS patients treated with pump implantation for refractory spasticity. Despite its size, this is one of the few reports anchored in an exclusively PLS population — not inferred from a larger mixed cohort. Patients showed sustained improvement in spasticity scores, tolerated the procedure, and managed the ongoing pump requirements. It is a modest piece of evidence, but it matters: it is direct confirmation, in the actual patient population, that the treatment the broader literature supports is viable in PLS specifically.
The rehabilitation angle is where the evidence is thinnest and the potential arguably largest. Physical therapy in PLS is typically managed as maintenance — protecting what function exists rather than recovering what has been lost. The 2021 case report of robot-aided gait training using the Lokomat-Pro system in a PLS patient challenged that framework. The patient underwent an intensive combined protocol — Lokomat exoskeleton plus conventional PT — and showed measurable improvements in spasticity severity, walking speed, and balance. A case report is the weakest form of evidence in the hierarchy; it cannot support a clinical recommendation on its own. But it is proof-of-concept that intensive technology-assisted gait training can produce functional gains in PLS, and it opens a question the field has not yet seriously pursued: what would a properly powered rehabilitation trial in PLS show?
What we know — and what we don't
The pharmaceutical evidence supports baclofen and tizanidine as roughly comparable first-line options with meaningfully different side-effect profiles. Intrathecal baclofen has demonstrated long-term efficacy for severe spasticity, including some direct PLS data. Cortical-origin spasticity — the PLS type — responds to ITB but requires higher doses and offers less predictable functional gains than spinal-origin disease.
What the evidence does not support is any claim that these treatments slow the progression of PLS. They manage the symptom; they do not modify the disease. And because PLS patients live for decades with their spasticity, the cumulative quality of that symptom management — the consistency of it, the side-effect burden it carries, the rehabilitation that surrounds it — matters enormously.
The genuine gap is at the rehabilitation end. Compared to stroke rehabilitation, MS rehabilitation, or even spinal cord injury rehabilitation, PLS-specific rehab evidence is nearly nonexistent. The Lokomat case report is a beginning, not a conclusion. There is no reason in principle why the principles of activity-dependent plasticity that have generated robust rehabilitation evidence in other UMN diseases could not be tested in PLS. That testing has not happened yet.
Why it matters for you
If you have PLS and spasticity is your dominant problem — as it is for most people with this disease — the research summarized here is the foundation on which your treatment decisions rest. It is worth understanding both what the evidence shows and where it comes from. The spasticity management guide translates this research into practical guidance on medications, doses, side effects, and escalation decisions. The treatments page covers the full spectrum of what is currently available, and the drug trials section looks at what might become available in the future.
Individual studies in this section
Full details on each study, including methods, findings, and context: