Spasticity & Neuroregression - CP-Like but Progressive
- HSP is a genetically heterogeneous group of inherited disorders of the corticospinal tracts (and dorsal columns) causing progressive lower-limb spasticity, hyperreflexia and a spastic gait.
- MLD is an autosomal-recessive lysosomal leukodystrophy (arylsulfatase A deficiency, sulfatide accumulation, central and peripheral demyelination) causing progressive neuroregression.
- The sequelae of both are spasticity-driven and CP-like: equinus and pes planovalgus, flexed-knee crouch, hip flexion/adduction with displacement, contractures and neuromuscular scoliosis.
- 70% of HSP children presenting under 3 years in an Alberta registry had first been diagnosed with cerebral palsy; suspect HSP in spastic diplegia without prematurity, IUGR, infection or vascular insult.
- Manage with the CP toolkit (tone management, orthoses, selective surgery, hip and spine surveillance), tailored to a progressive trajectory rather than a static baseline.
- There is essentially no condition-specific orthopaedic outcome evidence in either disease: every threshold is borrowed from CP.
- “HSP is a length-dependent 'dying-back' degeneration of the longest axons: legs first, hands spared, spasticity out of proportion to weakness.
- “SPG4 (SPAST, spastin, autosomal dominant) is the commonest HSP type.
- “MLD can show spasticity with absent or reduced reflexes: central demyelination plus a peripheral demyelinating neuropathy.
- “HSCT or gene therapy (arsa-cel, 'Libmeldy') given early can halt or slow MLD, leaving a more static, CP-like trajectory.
Overview: CP-Like Sequelae in a Progressive Disease
Hereditary spastic paraplegia (HSP) and metachromatic leukodystrophy (MLD) are different disorders that reach the orthopaedic clinic with the same spasticity, or upper-motor-neuron, picture. That picture produces the lower-limb problems of spastic cerebral palsy, and their management borrows its principles.
The sequelae. Lower-limb spasticity produces a pattern familiar from cerebral palsy:
- Equinus and pes planovalgus feet
- A flexed-knee "crouch" gait
- Hip flexion and adduction deformity, with the risk of hip displacement or subluxation
- Progressive contractures
- Neuromuscular scoliosis and other spinal deformity, more so in the more severely affected and in MLD
The difference from cerebral palsy. Cerebral palsy is static; HSP and MLD are progressive. The neurological deficit and the deformity worsen over time, in MLD often relentlessly.
Do not assume a stable baseline when planning surgery or setting goals. The natural history and prognosis should shape the timing and extent of surgery, the realistic functional aims and the intensity of surveillance, within a multidisciplinary team that includes neurology and genetics, and with honest discussion of the trajectory, especially in MLD.
HSP: Genetics and Classification
The disorder. HSP is a genetically heterogeneous group of inherited neurodegenerative disorders of the corticospinal tracts and dorsal columns. It causes progressive lower-limb spasticity, hyperreflexia and a spastic gait.
Why the legs, with power preserved. HSP is a length-dependent "dying-back" degeneration of the longest axons, the distal corticospinal tracts to the legs and the dorsal columns. The lower limbs are affected first, the hands are spared, and power is relatively preserved, so spasticity is out of proportion to weakness. That is what gives the orthopaedic problems their foot, knee and hip pattern.
Pure and complex forms. Pure (uncomplicated) HSP is a spastic paraparesis with, at most, dorsal-column sensory loss and urinary urgency. Complex (complicated) HSP adds features such as ataxia, cognitive impairment, peripheral neuropathy, epilepsy, retinopathy or a thin corpus callosum.
The SPG types. Genetic types are designated SPG1 to SPG80+, over 80 loci, and inheritance may be autosomal dominant, autosomal recessive, X-linked or mitochondrial. The commonest type and the other frequent ones:
- SPG4 (SPAST gene, spastin): autosomal dominant, and the commonest cause of pure adult-onset HSP
- SPG3A (atlastin): autosomal dominant, childhood-onset
- SPG11 (spatacsin): the commonest autosomal-recessive and complex form, with a thin corpus callosum
- SPG7 (paraplegin): autosomal recessive
MLD: Subtypes, the Mixed Nerve Picture, and Therapy That Changes the Trajectory
The disorder. MLD is an autosomal-recessive lysosomal storage leukodystrophy. Deficiency of arylsulfatase A leads to sulfatide accumulation with central and peripheral demyelination. The result is progressive neuroregression: loss of motor and cognitive skills, with evolving tone abnormalities (spasticity, sometimes preceded by hypotonia) and contractures.
The subtypes. Age of onset drives the speed of the disease: the later the onset, the slower the course.
- Late-infantile, the commonest: onset about 6 months to 2-3 years. A previously walking toddler regresses, with rapid motor and cognitive decline, often fatal within a few years.
- Juvenile: onset about 3-16 years. Cognitive and behavioural decline with gait problems, more slowly.
- Adult: onset over 16 years. A psychiatric or cognitive presentation, and the slowest course.
A mixed upper- and lower-motor-neuron picture. Central demyelination gives spasticity and hyperreflexia, but the peripheral demyelinating neuropathy gives lower-motor-neuron signs: weakness and, characteristically, absent or reduced reflexes. A child with spasticity and lost reflexes is showing a diagnostic clue. As the disease advances, the picture evolves towards hypotonia and areflexia.
Diagnosis. The diagnosis rests on:
- Low arylsulfatase A activity
- Raised urinary sulfatides
- ARSA gene testing
- MRI showing symmetric periventricular demyelination in a "tigroid" or leopard-skin pattern
- Nerve conduction evidence of a demyelinating neuropathy
Therapy that changes the trajectory. Two treatments can halt or slow the disease if given early. Haematopoietic stem-cell transplant is used for pre-symptomatic later-onset disease. Atidarsagene autotemcel (arsa-cel, "Libmeldy") is an ex-vivo autologous ARSA gene therapy for pre-symptomatic late-infantile and early-juvenile MLD; the Fumagalli series in the evidence below also treated early-symptomatic children.
The Child in Front of You Is Probably Labelled Cerebral Palsy
The registry. In an Alberta registry of 90 HSP families, 29 had a paediatric presentation of spasticity and 20 presented under 3 years. Fourteen families had received an initial diagnosis of cerebral palsy, amounting to 70 percent of those presenting under 3. For early-onset HSP, arriving under a CP label is the usual situation.
How the label is corrected. In every case it was corrected only after the symptoms progressed and prompted neurogenetic assessment, and exome sequencing identified a pathogenic variant in nine of the fourteen. An orthopaedic surgeon following a "CP" diplegia through serial gait and hip assessments is often the first clinician in a position to see that the picture is progressing rather than growing out of proportion. The diagnosis changes prognosis, surgical planning and the family's recurrence risk.
In a young child with spastic diplegia and no clear history of prematurity, intrauterine growth restriction, infection or vascular insult, consider HSP.
Management: The Cerebral-Palsy Toolkit in a Progressive Disease
The toolkit. Management is multidisciplinary and uses largely the same tools as spastic cerebral palsy, framed by the progressive natural history and realistic functional goals:
- Spasticity and tone management: physiotherapy, oral agents, botulinum toxin and, in selected cases, baclofen
- Orthoses: AFOs, and custom insoles for pes planovalgus and foot pressure
- Selective surgery: soft-tissue releases and lengthenings, foot reconstruction, hip surveillance and reconstruction, and scoliosis correction
Orthoses for the HSP foot. Children with HSP develop pes planovalgus and a flexed-knee gait, and foot orthoses are used to control plantar pressure and improve gait. The figures that follow come from the single-patient study that optimised personalised insoles for one such child.
The management is borrowed. There is essentially no condition-specific orthopaedic outcome evidence in HSP or MLD: no hip-surveillance series, no comparative results for soft-tissue or bony surgery, no scoliosis cohort, and no validated migration-percentage programme or threshold. Every threshold and protocol is imported from cerebral palsy, a static encephalopathy. That is a reasoned extrapolation rather than an evidence-based standard, and in a progressive disease a CP-derived threshold may act too late, so say so when asked.
Follow the trajectory. Serial gait, serial migration percentage and serial spinal assessment tell you more than any borrowed cut-off, so let the trajectory rather than a single measurement drive the decision. Set goals against the expected course.
The treated MLD child. Ask whether the child has had stem-cell transplant or gene therapy. A treated, stabilised child has a more static, CP-like trajectory and behaves far more like the population the protocols were written for, which shifts decision-making from purely palliative toward the standard surveillance and reconstruction used in cerebral palsy.
Where the borrowed principles come from. The pages these principles are borrowed from are the source of every threshold used here: cerebral palsy for the overall framework, cerebral palsy hip surveillance for the migration-percentage programme, cerebral palsy gait and single-event multilevel surgery for the crouch and lever-arm reasoning, spastic equinovarus foot for the foot, and neuromuscular scoliosis for the spine. The other inherited neuropathy that reaches a paediatric orthopaedic clinic with a progressive foot deformity is covered under hereditary motor and sensory neuropathies.
Mnemonics & Memory Aids
SPASTIC
Hook:SPASTIC: Spasticity/Storage, Progressive, Ankle (equinus/planovalgus), Stance (crouch), Tone management, (hip) Instability, Curve/Contractures (CP toolkit).
WRONGSuspect HSP over CP - WRONG
Hook:If the CP label feels WRONG - no perinatal cause, a family history, and a progressing course - think HSP: 70% of early-onset HSP was first called CP.
TIGERMLD at a Glance - TIGER
Hook:MLD is the TIGER: Tigroid MRI, Infantile-fastest, Gene therapy changes the course, Enzyme arylsulfatase A, Reflexes lost despite spasticity.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“How do the orthopaedic problems of hereditary spastic paraplegia and metachromatic leukodystrophy compare with cerebral palsy, and how does that change management?”
The disorders
- HSP: inherited corticospinal-tract disorder → progressive lower-limb spasticity + spastic gait
- MLD: autosomal-recessive lysosomal leukodystrophy (arylsulfatase A) → neuroregression
- Both progressive (unlike static cerebral palsy)
- 70 percent of HSP presenting under 3 years was first diagnosed as CP - suspect it without a perinatal cause
Orthopaedic sequelae (spasticity-driven)
- Equinus / pes planovalgus; flexed-knee crouch gait
- Hip flexion/adduction with hip displacement/subluxation; contractures
- Neuromuscular scoliosis
Management
- CP toolkit: tone management (physio/botulinum toxin/baclofen), orthoses/AFOs
- Selective surgery (releases/lengthenings, foot, hip/spine reconstruction); hip + spine surveillance
- Tailor goals/surgery timing/surveillance to the progressive trajectory; MDT (neurology/genetics)
- Every threshold is borrowed from CP - no condition-specific orthopaedic outcome evidence exists; follow the trajectory, not a cut-off
Evidence & Key Studies
Foot orthoses for pes planovalgus and flexed-knee gait in a child with hereditary spastic paraplegia
- Children with hereditary spastic paraparesis develop foot/lower-limb deformity (pes planovalgus and a flexed-knee gait), and customised foot orthoses are widely used to manage plantar pressure and improve structural support.
- Optimised personalised insoles substantially reduced peak plantar pressure and improved load distribution in a paediatric patient with HSP, pes planovalgus and flexed-knee gait.
- Orthotic management is a noninvasive intervention to prevent secondary complications and improve gait mechanics in HSP - reflecting the spasticity-driven, CP-like orthopaedic sequelae.
Hereditary spastic paraplegia initially diagnosed as cerebral palsy
- From an Alberta registry of 90 HSP families, individuals in 29 families had a paediatric presentation of spasticity and 20 presented under 3 years of age. Fourteen families had received an initial diagnosis of cerebral palsy - 70 percent of the children presenting under 3 - with the correct diagnosis made only after symptom progression prompted neurogenetic assessment.
- Whole exome sequencing identified pathogenic or likely pathogenic variants in nine of the fourteen cases across six genes; in the remaining five, progression and a positive family history made HSP the most likely diagnosis without a confirmed variant.
- The authors conclude that in a young child with spastic diplegia and no clear history of prematurity, intrauterine growth restriction, infection or vascular insult, HSP should be considered, because accurate diagnosis alters prognosis, management and recurrence risk. This is a registry chart review from one Canadian province and cannot give the proportion of all CP-labelled children who in fact have HSP.
Lentiviral haematopoietic stem-cell gene therapy (atidarsagene autotemcel) for early-onset MLD
- Integrated analysis of a phase 1/2 trial plus expanded access: 29 children with pre-symptomatic or early-symptomatic early-onset MLD treated with arsa-cel (autologous HSPCs transduced ex vivo with ARSA-encoding lentivirus), compared with a matched untreated natural-history cohort of 31.
- 26 treated patients were alive at median follow-up 3.16 years (0.64-7.51); two died of disease progression and one of a sudden event deemed unlikely to be treatment-related.
- ARSA activity in peripheral blood mononuclear cells rose a mean 18.7-fold (late-infantile) and 5.7-fold (early-juvenile) above baseline at 2 years, with sustained multilineage engraftment after busulfan conditioning.
- Gross motor function scores diverged favourably from the age-matched natural-history course - the basis for the page's claim that early gene therapy converts a relentless trajectory into a more static, CP-like one.
Outcome measures of instrumented gait analysis in hereditary spastic paraplegia: a systematic review
- PRISMA-2020 systematic review of 38 studies (2004-2024; 29 observational, 9 interventional) using instrumented gait analysis (motion capture and inertial sensors) in HSP.
- Walking speed and knee range of motion differentiate HSP from healthy controls but are general rather than disease-specific measures.
- Foot lift, foot range of motion and gait variability are the more disease-specific parameters, reflecting severity and balance deficit.
- No consensus HSP-specific digital outcome measure exists - which is why serial, same-method measurement beats any single borrowed cut-off.
The development of pes planovalgus and a flexed-knee gait in children with hereditary spastic paraplegia and the role of foot orthoses to manage plantar pressure and improve gait come from the cited Alsaleh report. The corticospinal-tract basis and progressive nature of HSP, the lysosomal (arylsulfatase A) basis and neuroregression of metachromatic leukodystrophy, the broader spasticity-driven CP-like sequelae (equinus, crouch, hip displacement, contractures, neuromuscular scoliosis), and management with the cerebral-palsy toolkit (tone management, orthoses, selective surgery, hip/spine surveillance) tailored to the progressive trajectory are standard, well-established teaching. The misdiagnosis figures come from the Suchowersky registry review, which is from a single Canadian province and describes the proportion of known HSP patients previously labelled CP - not the proportion of CP-labelled children who actually have HSP. The gene-therapy trajectory change comes from the cited Fumagalli arsa-cel trial (26 of 29 treated children alive at median 3.16 years, enzyme reconstituted 18.7-fold in the late-infantile variant), and the serial-measurement hierarchy from the cited Koch gait-analysis systematic review (foot lift, foot range of motion and gait variability are the disease-specific parameters). Beyond that, there is essentially no condition-specific orthopaedic outcome literature: no hip-surveillance series, no comparative results for soft-tissue or bony surgery, no scoliosis cohort, no validated migration-percentage threshold and no return-to-function data in either disease. Every protocol quoted here is imported from cerebral palsy, and the page says so rather than presenting borrowed thresholds as established for these conditions.