Photobiomodulation (low-level laser) in cerebral palsy

How photobiomodulation works

Photobiomodulation is the absorption of light photons by chromophores inside cells — most importantly cytochrome c oxidase in mitochondria — leading to increased ATP synthesis, balanced reactive oxygen species, modulation of inflammation, and downstream effects on neuroplasticity. The wavelengths used are red (around 630–700 nm) and near-infrared (around 800–1100 nm); near-infrared penetrates more deeply and is the range used when the goal is to influence deeper muscle or, transcranially, brain tissue.

PBM does not heat tissue and does not damage it. The biological story is biochemical and signalling, not thermal. That is what makes it tolerable for paediatric use and what gives it the safety profile reported across decades of research.

What it does in paediatric spastic cerebral palsy

In paediatric spastic CP, PBM has been studied mainly for two complementary goals. First, peripheral application targeting spastic muscle groups — most often gastrocnemius and hamstrings in lower-limb involvement — to reduce tone and provide a temporary window of improved range of movement during which physiotherapy can work more effectively. Second, transcranial application targeting motor cortex to support the cortical side of motor learning and to amplify the response to intensive task-specific therapy.

Systematic reviews report clinically meaningful reductions in modified Ashworth scale scores in selected protocols, with the strongest effect at 808–830 nm and around 1–5 J/cm² delivered over 8–12 sessions at 2–3 sessions per week. The effect is cumulative rather than immediate, with maximum benefit typically appearing around 4–6 weeks. Functional outcomes — gait speed, step length, GMFM-88 dimensions D (standing) and E (walking, running, jumping), and Pediatric Balance Scale — follow the reduction in spasticity when intensive rehabilitation is delivered alongside.

Why we combine PBM with intensive rehabilitation

The combination rationale is biological and behavioural. PBM lowers spasticity and improves muscle metabolism, creating a short window in which the child can be guided through higher-quality movement than is normally available to them. Intensive, goal-directed physiotherapy — including constraint-induced movement therapy, bimanual training, task-specific training, treadmill training, and where appropriate hippotherapy — uses that window to drive motor learning while the nervous system is in a more receptive state.

The evidence base from related rehabilitation literature supports this combination logic. Botulinum toxin A studies, action-observation training studies, and neurodevelopmental treatment (Bobath) protocols all show the same pattern: the technique alone is not what changes the long-term trajectory — the technique used to enable intensive, repetitive, goal-directed practice is what changes it. PBM fits into that template.

Safety and side effects

PBM has an exceptionally favourable safety profile across decades of paediatric use. Reported side effects are limited to mild local warmth or transient erythema at the application site, occasional mild headache, and brief sleep changes; all are transient. Eye protection is required during application and is standard in any properly run PBM service. PBM is not suitable in the presence of active malignancy at the application site or over open epiphyseal growth plates in some protocols; these are screened for routinely.

What we measure

Outcomes are measured with the same scales we use throughout cerebral palsy care: modified Ashworth and Tardieu for spasticity, GMFM-88 for gross-motor function, MACS for manual ability, CFCS for communication, EDACS for eating and drinking, Pediatric Balance Scale for balance, 10-metre and 6-minute walk tests for gait, and where appropriate gait analysis. Baseline, mid-block (week 4–6), end-of-block (week 12) and follow-up (3 and 6 months) are the standard checkpoints. Response is called response when the numbers move alongside the family's lived experience.

Where PBM does not fit

PBM is not the right step for every child. We do not recommend it where conventional intensive rehabilitation has not yet been optimised, where an unresolved orthopaedic or epilepsy problem should come first, where the clinical picture suggests no realistic motor target, or where families are being offered PBM by external providers in protocols that bypass the rehabilitation context altogether. Light without a rehabilitation programme around it tends to disappoint.

How an educational review can help

An educational review can pull together the current PBM literature in paediatric spastic cerebral palsy, frame the combined-approach evidence honestly, and prepare focused questions for your treating team — including whether PBM as part of an intensive rehabilitation block could be considered for your child. It is educational and does not replace your treating clinician's care.