Hereditary spastic paraplegia (HSP): stiff legs, genes and management

Signals for voluntary movement travel from the brain down the spinal cord along corticospinal tracts. The longest of these fibres supply the legs, and they are the ones most vulnerable in HSP. The NHS describes deterioration of the long spinal nerves that control lower body movement and muscle tone. When the brake signals from the brain are lost, the leg muscles become stiff and overactive, a state called spasticity, and they also become weak.

Because the damage is in the upper motor neurone, reflexes are brisk, ankles may jerk repeatedly, and toes may point upwards on stroking the sole. This is the opposite of what happens in conditions that damage the nerves outside the spinal cord, such as Charcot-Marie-Tooth disease.

In the pure form, the problem is limited to the legs and sometimes the bladder. The NHS lists gradual leg weakness, muscle stiffness and spasms, urinary urgency, possible foot numbness and walking difficulties such as stumbling.

Complicated forms bring extra features, depending on the gene: cognitive difficulty, epilepsy, neuropathy, eye problems, a thin corpus callosum on MRI and others. Because many different genes can be responsible, a gene panel is the usual route to an answer rather than testing one gene at a time.

• Walking becomes stiff, with toes catching on the ground

• High-arched feet are common

• Urgency of urine and sometimes constipation

• Upper limbs are usually spared in pure forms

• Symptoms can start in childhood, adolescence or adulthood

There is no single test for HSP. The NHS describes clinical examination, specialist tests including MRI scans of the brain and spine, and genetic testing to rule out similar conditions. MRI is important because other, treatable causes of spastic paraparesis must be excluded first, among them spinal cord compression, multiple sclerosis, vitamin B12 deficiency and primary lateral sclerosis.

A family history that fits autosomal dominant, recessive or X-linked inheritance supports the diagnosis, but a negative family history is common, either because of recessive inheritance, new changes or mildly affected relatives. NHS genetic testing is free when arranged by a hospital specialist, and genetic counselling is provided alongside it.

HSP can be inherited in autosomal dominant, autosomal recessive or X-linked patterns, depending on the gene. SPG4, the most common form, is autosomal dominant. MedlinePlus explains that the SPAST gene makes spastin, a protein that regulates microtubules, the cell structures involved in transport inside nerve cells, and that mutations impair transport particularly in neurons. Most people with SPG4 inherit it from a parent, but others have new mutations.

Severity in dominant families is variable. Some relatives have only mild stiffness late in life, while others are affected from childhood.

The NHS lists muscle relaxants, physiotherapy, occupational therapy, braces and occasionally surgery as options. Stretching and strengthening programmes help preserve range of movement and gait efficiency. Ankle-foot orthoses can reduce toe catching. Anti-spasticity medicines such as baclofen or tizanidine are taken orally, and in more severe spasticity a specialist may consider botulinum toxin injections or intrathecal baclofen delivered by a pump. Each is a specialist decision.

Urinary urgency is managed with bladder training, medicines and pelvic health advice. Falls prevention, appropriate footwear, a walking aid when helpful and adaptations at home and work protect independence. Fatigue and pain are common, and a rehabilitation team can address both.

The NHS states that pure HSP does not usually affect life expectancy and that many people live relatively independent lives, while prognosis for complicated forms depends on the individual symptoms. Most people eventually need a stick or walker, and some use a wheelchair for longer distances. Progress is typically gradual, over years or decades.