Motor Neurone Disease and Other Neurological Conditions

TL;DR. Motor neurone disease kills the neurons that carry the command to move, and only those. Sensation stays intact, the bladder usually works, the eyes keep moving, and in most patients the mind remains largely present, which means people watch themselves become paralysed while feeling everything. Median survival is two to three years from symptom onset, most people die of respiratory failure, and the only widely licensed drug extends life by a few months. What genuinely changes outcomes is not a drug: it is a multidisciplinary team, non-invasive ventilation, and feeding support, which together add substantially more time and far more quality than anything in a bottle. This chapter also covers several other neurological conditions the book has not reached, including two that are frequently missed and eminently treatable: Guillain-Barré syndrome and normal pressure hydrocephalus.

Key takeaways

• Motor neurone disease has a lifetime risk of roughly 1 in 300 to 400, which is far more common than most people assume, with a median survival of two to three years.
• It spares sensation, eye movement, and continence, which is why communication technology works and why the experience is one of being trapped rather than absent.
• Non-invasive ventilation adds around seven months of survival and improves quality of life, which is more than any approved drug.
• Guillain-Barré syndrome is an ascending paralysis that is treatable, and uniquely among inflammatory neurological diseases, corticosteroids do not work and should not be used.
• Normal pressure hydrocephalus is a reversible cause of a dementia-like picture, and its gait disturbance comes first, which is the diagnostic clue.
• Bell's palsy involves the forehead; a stroke usually spares it. That single distinction separates a benign condition from an emergency.

Motor neurone disease

In short: Progressive death of the neurons controlling voluntary movement, sparing everything else, and fatal within a few years.

What it is

Motor neurone disease (MND), called amyotrophic lateral sclerosis (ALS) in North America and in most research literature, is a progressive neurodegenerative disease of the motor system.

The motor pathway has two neurons in series: an upper motor neuron running from the brain's motor cortex down to the spinal cord, and a lower motor neuron running from the spinal cord to the muscle. MND destroys both, and the mixture of signs from the two is what makes the diagnosis.

Finding both patterns in the same limb, without sensory loss, is the signature of MND, and it occurs in very few other conditions.

The variants, which differ in prognosis:

What it does not do, which matters

MND characteristically spares:

• Sensation. Touch, pain, and temperature remain normal. This is why pressure sores are agonising, and it is a key diagnostic feature.
• Eye movements, until very late, which is what makes eye-tracking communication devices viable.
• Bladder and bowel control, usually.
• Consciousness and, in most patients, the majority of cognition.

The cognitive picture is more complicated than the classic teaching. Around 15 percent of patients develop frontotemporal dementia, and up to half have some measurable change in executive function, language, or behaviour. MND and frontotemporal dementia are now understood as two ends of one disease spectrum, sharing the same underlying protein pathology and, in many familial cases, the same gene.

What actually goes wrong

TDP-43 is the central protein. In roughly 97 percent of ALS cases, this protein, normally resident in the nucleus, mislocalises to the cytoplasm and forms aggregates. The same pathology is found in the majority of frontotemporal dementia cases, which is what unified the two conditions.

Several processes are implicated and none is established as the initiating event: protein misfolding and impaired clearance, RNA processing failure, glutamate excitotoxicity (overstimulation of motor neurons, and the rationale for riluzole), mitochondrial dysfunction, oxidative stress, impaired axonal transport along the very long axons these neurons maintain, and neuroinflammation.

Genetics. Roughly 10 percent of cases are familial, and a proportion of apparently sporadic cases also carry causative variants:

What it does over time

Onset is usually focal: weakness in one hand, a foot drop, or slurred speech. It then spreads, typically to contiguous body regions.

Respiratory failure is the usual cause of death, and it is typically peaceful, with rising carbon dioxide producing drowsiness and then unconsciousness.

Is it deadly?

Yes, and predictably.

• Median survival is 2 to 3 years from symptom onset, roughly 2 years from diagnosis given typical diagnostic delay.
• About 10 percent live more than 10 years.
• Bulbar onset and older age at onset predict shorter survival; younger onset, limb onset, and primary lateral sclerosis predict longer.
• Stephen Hawking, who lived 55 years with the disease, is an extreme statistical outlier, and his case is frequently and misleadingly cited to newly diagnosed patients.

Is it contagious?

No. Motor neurone disease is not transmissible.

The TDP-43 protein spreads within one nervous system in a prion-like templating manner, which explains the contiguous anatomical progression, and this does not mean person-to-person transmission. No excess risk has been demonstrated in carers, spouses, or clinicians.

Clusters have been reported and investigated repeatedly, including elevated rates among professional footballers, military veterans of certain deployments, and historically among the Chamorro people of Guam. Proposed explanations have included head injury, pesticide exposure, intense physical activity, and environmental toxins, and no cause has been established.

Who gets it

• Incidence roughly 2 to 3 per 100,000 per year; prevalence is lower than incidence would suggest because survival is short.
• Lifetime risk approximately 1 in 300 to 1 in 400.
• Age: peak onset 55 to 75.
• Sex: slightly more men, roughly 1.2 to 1.5 to 1.
• Risk factors with some evidence: smoking, family history, and possibly military service, repeated head injury, and certain occupational exposures. The evidence for most environmental factors is weak and inconsistent.

Treatment, and how it works

In short: Two modest drugs, one gene-specific therapy, and three non-drug interventions that do more than any of them.

Palliative care from diagnosis, not at the end. As in Chapter 26, early palliative involvement improves symptoms and quality of life, and in a disease with this trajectory it also allows advance planning while communication is still easy.

Advance decisions matter unusually much here. Decisions about ventilation, feeding, and resuscitation are far better made early, in discussion, than in an emergency department at 3 a.m. Some patients choose tracheostomy ventilation, which can extend life for years at the cost of total dependence and, eventually, sometimes a locked-in state; most do not. MND is also central to assisted dying debates in every country that has had one, for reasons this chapter's clinical description makes obvious.

Living with it

The distinctive cruelty of MND is that it removes function while leaving the person intact to observe it. Loss of speech is frequently rated as the hardest single loss, because it removes the means of expressing everything else.

Carers, usually a spouse, provide enormous amounts of physical care over a short and intense period, and carer strain in MND is among the highest measured in any condition. Practical support, equipment provided before it is needed rather than after, and rapid access to a specialist team make the largest difference.

What's next

• Antisense oligonucleotides for other genetic forms, particularly C9orf72, following the SOD1 precedent.
• Neurofilament light chain as a biomarker for diagnosis, prognosis, and trial endpoints, which is already changing how trials are designed.
• Platform trials testing several drugs simultaneously against a shared control arm, which is how a rare, rapidly fatal disease can be studied efficiently.
• Earlier diagnosis. Average delay from symptom onset to diagnosis remains around a year, which is a large fraction of the remaining life and of the window for treatment.

Guillain-Barré syndrome

In short: An ascending paralysis after an infection, which is treatable, can stop breathing within days, and is the one inflammatory neurological disease where steroids do not work.

What it is. An acute immune attack on the peripheral nerves, usually following an infection by one to three weeks. The immune response to the infection cross-reacts with nerve components, a clean example of molecular mimicry (Chapter 49).

Triggers: Campylobacter jejuni (the commonest, and a reason food poisoning matters, Chapter 34), cytomegalovirus, Epstein-Barr virus, Mycoplasma, Zika virus, influenza, and, rarely, vaccines at rates far below the risk from the infections themselves.

What it does. Ascending symmetrical weakness starting in the legs, with loss of reflexes, progressing over hours to days and reaching its worst within four weeks by definition. Often with back pain and tingling. Then:

• Respiratory muscle failure in around 20 to 30 percent, requiring ventilation. This is what makes it an emergency.
• Autonomic instability: dangerous swings in heart rate and blood pressure.
• Bulbar weakness: swallowing and speech.

Miller Fisher variant presents differently, with eye movement paralysis, ataxia, and areflexia.

Treatment: intravenous immunoglobulin or plasma exchange, which are equally effective and are not combined. Plus close supportive care: monitoring respiratory function with regular vital capacity measurements rather than waiting for breathlessness, cardiac monitoring, and clot prevention.

Don't be confused: corticosteroids do not work in Guillain-Barré syndrome. This is genuinely surprising, since steroids help most inflammatory neurological conditions, and trials have consistently shown no benefit and possibly harm. It is a rare instance where the obvious treatment is the wrong one.

Outcome: most patients recover substantially, over weeks to months. Roughly 20 percent are left with significant disability, and mortality is around 3 to 7 percent even with modern care, mostly from respiratory and autonomic complications.

CIDP (chronic inflammatory demyelinating polyradiculoneuropathy) is the chronic relapsing counterpart, evolving over more than eight weeks, and unlike Guillain-Barré it does respond to steroids as well as to immunoglobulin.

Cerebral palsy

In short: A non-progressive injury to the developing brain producing a permanent movement disorder, and the commonest physical disability of childhood.

What it is. A group of permanent disorders of movement and posture caused by a non-progressive disturbance in the developing fetal or infant brain. It affects roughly 2 to 3 per 1,000 live births.

The word non-progressive is precise and often misunderstood. The brain lesion does not worsen. The musculoskeletal consequences do: spasticity causes contractures, hips can dislocate, scoliosis develops, and pain accumulates. So the underlying condition is static and the person's function can deteriorate without intervention, which is why lifelong follow-up matters.

Types:

Severity is described by the Gross Motor Function Classification System, levels I (walks without limitation) to V (transported in a wheelchair, no independent mobility), which predicts far more about a person's life than the subtype does.

Causes. Contrary to widespread assumption and to a great deal of litigation, birth asphyxia accounts for a minority, on the order of 10 percent. Most cases originate before labour: prematurity and low birth weight (the largest single risk factor), intrauterine infection, placental problems, multiple pregnancy, congenital brain malformation, and perinatal stroke.

Prevention that works: magnesium sulphate given to women in preterm labour reduces cerebral palsy in the baby, and therapeutic hypothermia (cooling newborns with hypoxic-ischaemic encephalopathy to around 33.5 degrees for 72 hours) reduces death and disability. Both are established and both are relatively recent.

Management: physiotherapy and occupational therapy; spasticity treatment with botulinum toxin injections, oral baclofen, intrathecal baclofen pumps, or selective dorsal rhizotomy (cutting selected sensory nerve roots) in carefully chosen children; hip surveillance programmes, which have dramatically reduced hip dislocation where implemented; orthopaedic surgery; communication support; and treating the frequently co-occurring epilepsy, feeding difficulty, pain, and learning disability.

Important framing: intelligence in cerebral palsy varies across the full range, and many people with severe motor impairment have entirely typical cognition. Assuming otherwise on the basis of speech difficulty or posture is a common and damaging error.

Normal pressure hydrocephalus

In short: A treatable condition that looks like dementia, and the gait comes first.

What it is. Enlargement of the brain's fluid-filled ventricles with normal or intermittently raised pressure, producing a characteristic triad:

1. Gait disturbance: a slow, broad-based, shuffling "magnetic" gait, as though the feet are stuck to the floor. This usually comes first, and it is the feature that responds best to treatment.
2. Urinary incontinence, typically urgency progressing to indifference.
3. Cognitive impairment, usually of the slowed, apathetic, executive type rather than the memory-first pattern of Alzheimer's disease.

The mnemonic taught for a century is "wet, wacky, and wobbly", and the useful correction is that wobbly comes first.

Why it matters. It is one of the few reversible causes of a dementia-like picture. It is treated by inserting a shunt to drain fluid from the ventricles to the abdomen, and selected patients improve substantially, particularly in gait.

The difficulty is selection. Ventricles enlarge with age and with brain atrophy in general, so imaging alone over-diagnoses it. Response is predicted by a large-volume lumbar puncture or external drainage trial: if removing fluid temporarily improves the gait, a shunt is more likely to help. Coexisting Alzheimer pathology is common and reduces the benefit.

Shunts carry real risks including infection, blockage, and over-drainage, so this is a genuine risk-benefit judgement rather than an obvious win.

Prion diseases

In short: A misfolded protein converting its normal counterpart into copies of itself, producing rapid fatal dementia, and it is transmissible.

Prions are the fourth kind of pathogen from Chapter 14: proteins with no genetic material, which cause disease by converting the normal cellular version of the same protein into the misfolded form, which then does the same to others. It is a chain reaction made of protein.

Creutzfeldt-Jakob disease (CJD) occurs in four forms:

Clinically: rapidly progressive dementia over weeks to months, with myoclonus (sudden jerks), ataxia, visual disturbance, and akinetic mutism. Median survival in sporadic CJD is about four to six months. Variant CJD affected younger people and progressed more slowly, often presenting with psychiatric symptoms and sensory disturbance.

There is no treatment. The public health significance is transmissibility: prions resist normal sterilisation, which is why neurosurgical instruments used on suspected cases are destroyed and why people who received certain medical products or lived in the UK during the BSE years are excluded from blood donation in several countries.

Kuru, transmitted by funerary cannibalism among the Fore people of Papua New Guinea, and studied by Carleton Gajdusek, was the disease that established that these conditions were transmissible, and Stanley Prusiner's identification of the protein mechanism won the 1997 Nobel Prize.

Two common conditions worth recognising

In short: Bell's palsy and trigeminal neuralgia, both dramatic, both treatable, and both frequently mismanaged.

Bell's palsy is sudden weakness of one side of the face from inflammation of the facial nerve, probably usually viral. It affects roughly 20 to 30 people per 100,000 per year.

Don't be confused: the forehead is the distinguishing feature. In Bell's palsy the forehead is involved, so the person cannot raise that eyebrow or wrinkle that side of the forehead. In a stroke affecting the face, the forehead is usually spared, because that part of the face receives input from both sides of the brain. Sudden facial weakness with a spared forehead, or with any other neurological symptom, should be treated as a stroke until proven otherwise (Chapter 22).

Treatment: corticosteroids started within 72 hours improve the chance of complete recovery, which makes it time-sensitive. Antivirals add little. Eye protection is essential and frequently neglected: if the eye will not close, the cornea dries and ulcerates, so lubricant drops and taping the eye shut at night prevent a permanent injury. Around 70 percent recover completely, and recovery is better in younger patients with incomplete palsy.

Trigeminal neuralgia causes sudden, severe, electric-shock-like facial pain lasting seconds, triggered by light touch, chewing, cold air, or brushing teeth. It is usually caused by a blood vessel compressing the trigeminal nerve root, and in younger patients it can be a presenting feature of multiple sclerosis (Chapter 40).

It is among the most severe pains described in medicine, historically called "the suicide disease", and it is treatable. Carbamazepine is first-line and usually effective. For refractory cases, microvascular decompression, an operation placing a cushion between the vessel and the nerve, offers durable relief in the majority. Ordinary painkillers, including opioids, do not work, which is a common source of mismanagement.

What the person can do

In short: Recognise the time-critical ones, and get to a specialist team early in the chronic ones.

• Progressive painless weakness without sensory loss warrants urgent neurological assessment. Diagnostic delay in MND averages around a year, which is a large share of the time available.
• Rapidly ascending weakness with loss of reflexes over days, especially after a diarrhoeal illness, is an emergency. Guillain-Barré can stop breathing, and the deterioration can be fast.
• Sudden facial weakness: check the forehead. If it is spared, or if there is any other symptom, treat it as a stroke and call emergency services. If Bell's palsy is likely, seek care within 72 hours to get steroids, and protect the eye immediately.
• A shuffling magnetic gait with incontinence and cognitive change deserves specific consideration of normal pressure hydrocephalus rather than assuming dementia.
• In MND, get to a specialist multidisciplinary clinic early, accept equipment and ventilation assessment before you feel you need them, discuss feeding before swallowing becomes unsafe, bank your voice while you can, and make advance decisions while communication is easy.
• In cerebral palsy, insist on hip surveillance for children, which prevents a common and painful complication.

Sources and notes

MND/ALS incidence, lifetime risk, and survival: Hardiman et al., Nature Reviews Disease Primers, 2017, and Brown and Al-Chalabi, NEJM, 2017. TDP-43 pathology: Neumann et al., Science, 2006. C9orf72: DeJesus-Hernandez et al. and Renton et al., Neuron, 2011. SOD1: Rosen et al., Nature, 1993. Riluzole effect size: Cochrane review. Non-invasive ventilation survival benefit: Bourke et al., Lancet Neurology, 2006. Multidisciplinary clinic and survival: Traynor et al., and subsequent cohorts. Tofersen: VALOR trial and FDA accelerated approval, 2023. ALS-FTD spectrum frequencies: Phukan et al. and Ringholz et al. Guillain-Barré epidemiology, treatment equivalence of IVIG and plasma exchange, and the ineffectiveness of steroids: Cochrane reviews and Willison, Jacobs, and van Doorn, The Lancet, 2016. Cerebral palsy prevalence and aetiology: Graham et al., Nature Reviews Disease Primers, 2016; intrapartum asphyxia as a minority cause is well established in the epidemiological literature. Magnesium sulphate neuroprotection: Doyle et al., Cochrane review. Therapeutic hypothermia: TOBY and CoolCap trials. Normal pressure hydrocephalus selection and outcomes: international guidelines and shunt outcome series. Prion diseases: Prusiner, Nobel Lecture, 1997; UK vCJD case counts from the National CJD Research and Surveillance Unit. Bell's palsy steroids: Sullivan et al., NEJM, 2007. Trigeminal neuralgia and microvascular decompression: Zakrzewska and Linskey reviews.

Open questions. What initiates sporadic motor neurone disease is unknown. Whether reported disease clusters reflect genuine environmental causes has never been resolved. Which patients with normal pressure hydrocephalus will benefit from shunting remains difficult to predict.

Next: the most common diseases in this book, and the ones most often dismissed. 👉