Motor Neuron Disease (ALS)

Overview & Definition

Use the terms precisely. MND is the umbrella used for classical ALS, primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), bulbar-predominant presentations and regional phenotypes. ALS is the commonest adult MND phenotype; it usually shows progressive clinical or electrophysiological LMN dysfunction together with clinical UMN dysfunction, but either component may be subtle early.[1][2]

The examination pattern is a progressive motor syndrome: weakness, wasting and fasciculations suggest LMN involvement; spasticity, pathologically brisk reflexes, clonus and extensor plantar responses suggest UMN involvement. Mixed signs need not occur in the same limb at first presentation. Spread to another region, loss of function over time and absence of a better explanation are more important than a memorised stereotype.[1][2]

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Classification — four subtypes that differ by prognosis

[1] [11] [1] [3]

ALS-FTD lies on the ALS-frontotemporal spectrum, particularly with C9orf72 expansions. Flail arm and flail leg are regional phenotypes that may remain regionally restricted for a prolonged period; prognosis must therefore be individualized rather than inferred from a single label.[12][13]

How common, and who

ALS incidence, age distribution, sex ratio and gene frequencies vary by population and ancestry. A reasonable teaching estimate in European-ancestry populations is roughly 1.5–2.5 new cases per 100,000 people per year, while familial disease accounts for about 5–10% by family history; a pathogenic variant may still be found in a person without an affected relative.[1][4]

Most ALS remains apparently sporadic and multifactorial. Smoking and some occupational or environmental exposures have epidemiological associations, but association does not establish a single cause in an individual. Avoid presenting head trauma, pesticides, military service or cyanobacterial toxins as proven patient-level causes.[1]

Why motor neurons die — four convergent mechanisms

ALS is biologically heterogeneous. Converging mechanisms include impaired RNA processing and protein homeostasis, glutamate excitotoxicity, mitochondrial dysfunction, oxidative stress, axonal transport failure and non-cell-autonomous glial injury. Cytoplasmic TDP-43 pathology is common in ALS and frontotemporal lobar degeneration, but important genetic subgroups, including many SOD1- and FUS-associated cases, have different dominant pathology.[1][13]

Corticospinal and corticobulbar pathway dysfunction produces UMN signs; loss of cranial motor nuclei and spinal anterior horn cells produces LMN signs. Relative resistance of sensory, ocular-motor and sacral motor systems explains the classical examination pattern, but it must not be turned into an “always spared” rule.[1]

[1] [13]

Meet the patient at the bedside — by region of onset

Limb, bulbar and respiratory presentations

Limb-onset ALS commonly begins with painless focal weakness, loss of dexterity, foot drop, cramps or fasciculations and then spreads. A brisk reflex in a wasted limb strongly supports mixed motor-system involvement, but an early limb may show only LMN or only UMN signs.[1]

Bulbar involvement causes dysarthria, dysphagia, impaired cough, drooling from ineffective handling of saliva and sometimes pseudobulbar affect. Tongue wasting or fasciculations support bulbar LMN dysfunction; a slow, strained voice and brisk jaw jerk support corticobulbar UMN dysfunction. Many patients have a mixed pattern.[1][3]

Respiratory involvement may present with orthopnoea, breathlessness, weak cough, unrefreshing sleep, morning headache, nightmares, daytime somnolence or recurrent chest infection. These symptoms can precede a markedly reduced upright FVC, especially with bulbar or diaphragmatic weakness.[3]

Cognitive and behavioural involvement

ALS is not a purely motor disease. Overt ALS-FTD occurs in a minority, often taught as roughly 10–15%, while milder executive, language or behavioural change occurs in a substantially larger group.[11][12] Screen with the Edinburgh Cognitive and Behavioural ALS Screen (ECAS) or ALS Cognitive Behavioral Screen (ALS-CBS) and obtain an informant history. Capacity is decision-specific: cognitive impairment does not automatically remove capacity, and communication support must precede judgment.[11]

Classical relative sparing — and its limits

Objective sensory loss, early prominent sphincter dysfunction and a primary ocular-motor disorder are atypical dominant features and should trigger mimic review. However, sensory symptoms or subclinical abnormalities, urinary urgency and late ocular-motor changes can occur. Mild sensory NCS abnormalities do not by themselves exclude ALS. Cognition is not a spared system.[1][3][11]

The differential — the highest-yield viva ground in MND

The closest treatable or structurally remediable mimics are:[1][3]

[1] [3]

Other pattern-directed exclusions include inflammatory motor neuropathy, structural brainstem or spinal lesions, endocrine/metabolic disease, B12 or copper deficiency with sensory myelopathy, infection where exposure supports it, adult-onset spinal muscular atrophy, hereditary spastic paraplegia and riboflavin-transporter deficiency in an appropriate young phenotype.[1]

The bedside assessment — show UMN and LMN across regions

Map findings across bulbar, cervical, thoracic and lumbosacral regions. Document weakness, wasting, fasciculations, tone, reflexes, plantar responses, speech, swallow, neck/trunk strength and cough. Examine sensation, ocular movements and sphincter history to identify atypical features rather than to enforce an absolute exclusion rule.[2]

At each review ask about breathing during sleep and when supine; record weight trajectory, meal duration, choking, hydration, communication, mobility, pain, cramps, spasticity, secretions, mood, cognition, behaviour, caregiver strain and the patient’s goals.[3]

ALSFRS-R

The ALS Functional Rating Scale–Revised (ALSFRS-R) has 12 items, each scored 0–4, giving a total of 0–48 where higher scores indicate better function. Items cover speech, salivation, swallowing, handwriting, cutting food/handling utensils, dressing and hygiene, turning in bed, walking, stairs, dyspnoea, orthopnoea and respiratory insufficiency.[10]

[10] [11]

Use serial scores and the slope to describe function and inform prognosis or trial outcomes, but do not assume linear decline in every patient. ALSFRS-R does not assess cognition, behaviour, caregiver burden or the complete respiratory picture.[10][11]

Investigations — a clinical diagnosis, EMG-supported, mimic-excluding

Gold Coast diagnostic framework

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For a region to count as LMN-involved, abnormalities must be present in either two limb muscles supplied by different roots and nerves or one bulbar or thoracic muscle, according to the Gold Coast proposal.[2] Clinical UMN dysfunction is defined by pathologically brisk or spreading reflexes, pathological reflexes, spasticity or slowed poorly coordinated voluntary movement not explained by LMN weakness.[2]

EMG and nerve conduction studies

Needle EMG samples clinically involved and uninvolved regions. ALS-compatible LMN dysfunction combines chronic neurogenic change with ongoing denervation, which may include fibrillation potentials, positive sharp waves or fasciculation potentials in the appropriate neurogenic context. Fasciculations in isolation are not diagnostic.[2]

NCS help exclude demyelinating motor neuropathy, conduction block and a prominent sensory neuropathy. Motor conduction block supports MMN; its absence does not eliminate MMN, and mild sensory abnormalities do not automatically eliminate ALS. EMG sensitivity is imperfect in bulbar- or UMN-predominant disease and no electrophysiological pattern independently proves ALS.[2][3]

Imaging, laboratory and genetic work-up

Choose investigations to test plausible alternatives raised by age, tempo, distribution, atypical sensory/autonomic/ocular features, exposure history and electrophysiology. Use brain or spine MRI when a structural mimic is plausible, and select laboratory, CSF, neuromuscular-junction, muscle or other tests only when the clinical pattern indicates them. There is no universal ALS imaging or laboratory panel, and no test independently confirms ALS.[1][2]

Offer genetic testing to every person with ALS after pre-test education and counselling. A minimum diagnostic assay should cover C9orf72 repeat expansion plus SOD1, FUS and TARDBP, with a broader validated panel where appropriate. Explain consent, incomplete penetrance, variants of uncertain significance, possible insurance/social implications and consequences for relatives; provide post-test counselling.[4] Predictive testing of an unaffected relative should follow identification of a familial pathogenic variant and formal counselling, not occur automatically.[4]

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Suspected ventilatory failure

Treat orthopnoea, morning headache, somnolence, disturbed sleep, weak cough, rising bicarbonate or hypercapnia as possible neuromuscular ventilatory failure. Check pulse oximetry, sitting and supine VC/FVC, SNIP or MIP, and blood gases or nocturnal oximetry/capnography when indicated; do not wait for one isolated FVC value.[3]

Offer non-invasive ventilation (NIV) when symptoms, signs or investigations support respiratory insufficiency, regardless of bulbar status; bulbar dysfunction may make interface and secretion management harder but is not an exclusion.[3] The NICE NG42 respiratory table uses VC/FVC below 50% predicted, or below 80% with respiratory symptoms/signs, SNIP/MIP below 40 cmH2O, or sex-specific pressure thresholds with symptoms as prompts for discussion and further assessment—not as a single universal gate.[3]

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Assess cough and secretions. Escalate from positioning, hydration/humidification and manually assisted cough or unassisted breath-stacking to assisted breath-stacking/lung-volume recruitment and mechanical insufflation–exsufflation when simpler measures are inadequate; use suction as an adjunct and treat saliva or thick secretions.[3]

[3] [7] [9]

Management — Definitive & Stepwise

Disease-modifying therapy

Riluzole is recommended for ALS at 50 mg orally twice daily. Randomized-trial evidence supports a modest aggregate survival benefit, commonly taught as roughly 2–3 months; the Cochrane estimates must not be misquoted as the false hybrid “HR 0.80, 95% CI 0.70–0.99.”[5] Obtain baseline liver tests, monitor regularly during early treatment and through the first year, then periodically according to the current local label; stop and seek specialist advice for clinically important hepatic injury or label-defined marked transaminase elevation.[3][5]

Edaravone has jurisdiction-specific authorization and guideline use. The pivotal trial randomized 137 highly selected participants and found 2.49 fewer ALSFRS-R points of decline over 24 weeks; entry included disease duration no more than 2 years, FVC at least 80% predicted and preserved individual ALSFRS-R items.[6] In the US, the current IV/oral schedule uses daily treatment for 14 days followed by 14 drug-free days in cycle 1, then treatment on 10 of 14 days followed by 14 drug-free days in later cycles; consult the FDA Drugs@FDA Radicava ORS record for formulation, fasting, feeding-tube and hypersensitivity/sulfite warnings.[6] FDA/PMDA authorization does not equal universal recommendation: the EAN 2024 guideline does not recommend edaravone outside trials in its setting.[3]

Tofersen is genotype-specific therapy only for ALS with a pathogenic SOD1 mutation. VALOR missed its prespecified week-28 ALSFRS-R primary endpoint but reduced CSF SOD1 protein and plasma neurofilament light; open-label-extension clinical findings are exploratory rather than proof of slowed progression.[7] The FDA accelerated approval rests on the neurofilament surrogate; the EU EMA Qalsody authorization is under exceptional circumstances. The label dose is 100 mg intrathecally, with 3 loading doses 14 days apart then maintenance every 28 days; specialist counselling must cover myelitis/radiculitis, papilloedema or raised intracranial pressure and aseptic meningitis.[7]

AMX0035 is not current routine ALS therapy. Sodium phenylbutyrate/taurursodiol (Relyvrio/Albrioza) failed the PHOENIX phase 3 trial, was removed from the US and Canadian markets in 2024, and FDA formally withdrew the Relyvrio approval effective 29 August 2025 at the manufacturer’s request; see the Federal Register withdrawal notice. It should not appear on a current treatment list.[3]

Nutrition, swallowing and gastrostomy

Monitor weight/BMI trajectory, intake, hydration, meal duration, choking and aspiration risk at multidisciplinary reviews. Speech-language/swallow assessment and dietetics guide texture modification, energy density, supplements, posture and safer feeding.[3]

Discuss gastrostomy early and revisit it according to swallowing burden, aspiration/choking, hydration, weight trajectory, respiratory status and patient preference. FVC 50% is not a universal deadline or contraindication. Respiratory impairment increases procedural risk; optimize/establish NIV and use ventilatory support during the procedure when needed. PEG, RIG or PIG choice is individualized, and ProGas found broadly similar procedural safety between methods.[9] The strongest goals are reliable nutrition, hydration and medication access and reduced meal burden; survival evidence is observational and confounded.[9] Oral intake for pleasure may continue only if consistent with the person’s swallowing risk and goals.

Communication, mobility and symptom control

Refer early to speech-language therapy for communication assessment, message/voice banking and augmentative and alternative communication; move to switch access or eye-gaze systems as limb and bulbar function change.[3] Physiotherapy and occupational therapy address stretching, positioning, contracture prevention, falls, orthoses, seating, wheelchairs, environmental control and caregiver handling.[3]

Treat symptoms with individualized ladders rather than unsupported fixed prescriptions:[3]

• Spasticity: stretching, positioning and physiotherapy; consider baclofen, tizanidine, gabapentin or locally licensed cannabinoids while monitoring sedation and worsened weakness.[3]
• Sialorrhoea: swallowing/posture measures, then a comorbidity-appropriate anticholinergic; specialist botulinum toxin and occasionally radiotherapy for refractory symptoms.[3]
• Thick secretions: hydration/humidification, review drying medicines, mucolytic strategies, assisted cough and suction.[3]
• Pseudobulbar affect: distinguish it from depression and FTD; dextromethorphan/quinidine where licensed or an individualized SSRI/TCA may be considered with interaction review.[3]
• Cramps, pain, mood and sleep: identify mechanism and use non-drug measures first where appropriate. For disabling cramps that persist, EAN 2024 says a monitored low-dose quinine sulfate trial (100–200 mg/day) may be considered.[3] This is not universal routine prescribing: follow current local authorization/product information, screen for jurisdiction-specific contraindications and interactions, and perform the cardiac monitoring recommended by EAN.[3]

Specialist multidisciplinary care

The core team includes neurology, an MND specialist nurse, respiratory care, dietetics, speech-language/swallow and communication expertise, physiotherapy, occupational therapy, psychology/neuropsychology, social care and palliative care.[3] Specialist MDT care is guideline-recommended and associated with better coordination, access and observational survival advantage, but an exact causal “7–9 month benefit” should not be claimed from non-randomized studies.[3]

Progressive bulbar palsy (PBP) — predominant bulbar UMN and LMN signs in an older patient, often female. PBP carries the worst prognosis of the MND subtypes — median survival is often under 2 years, because respiratory involvement develops early and aspiration is frequent. NIV is offered but is less effective in this group; PEG is almost always needed.[1][2]

PMA: a clinical LMN syndrome. Reassess if definite UMN signs emerge and actively exclude MMN, adult-onset spinal muscular atrophy, SBMA and other motor neuropathies or genetic phenocopies.[1][3]

PLS: a progressive UMN syndrome defined over time after exclusion of structural, inflammatory and hereditary causes and without significant active LMN degeneration. Do not teach “near-normal life expectancy” or a fixed conversion percentage as universal.[3]

Bulbar-predominant disease: distinguish bulbar-onset ALS from the historically variable PBP label; determine whether bulbar signs are UMN, LMN or mixed, and prioritize communication, swallowing, secretion, cough and respiratory support.[3]

ALS-FTD or major behavioural change: obtain an informant history, use an ALS-adapted screen, simplify care routines, support communication, assess each decision’s capacity and involve a proxy/advance directive according to law and the person’s wishes.[11][12]

Complications & Pitfalls

1. Overabsolute diagnosis: “sensation, eyes and sphincters are always spared” is false; prominent early abnormalities prompt mimic review but exceptions occur.[1]
2. Compulsory EMG myth: Gold Coast permits clinical or EMG evidence of LMN dysfunction; EMG supports and extends the examination but does not independently prove ALS.[2]
3. Fixed FVC gate: symptoms, supine testing, inspiratory pressures, nocturnal assessment and gas exchange matter; do not deny NIV or delay gastrostomy solely because FVC is above or below one number.[3][9]
4. Oxygen alone: oxygen can conceal/worsen hypercapnic ventilatory failure unless an indication is treated alongside adequate ventilation.[14]
5. Approval equals recommendation: edaravone and tofersen access, evidence and authorization differ by jurisdiction; genotype-specific accelerated approval is not proof of a positive functional endpoint.[3][7]
6. Outdated therapy: AMX0035 has been withdrawn and is not routine current care (Federal Register).[3]

Prognosis — uniformly fatal, but not uniform in pace

For ALS, median survival from symptom onset is often taught as about 2–5 years (commonly 3–5 years), but the range is wide.[1] Prognosis depends on phenotype, genotype, age, bulbar or respiratory onset, cognition/behaviour, nutritional trajectory, respiratory function and ALSFRS-R slope. PLS and some regional phenotypes can be much slower; therefore do not apply classical ALS survival statistics to the entire MND umbrella.[1][10]

Admission or urgent specialist review is appropriate for suspected ventilatory failure, inability to maintain hydration/nutrition, aspiration or infection, rapidly failing communication or mobility, uncontrolled symptoms or caregiver breakdown. Routine follow-up remains multidisciplinary and proactive rather than crisis-driven.[3]

Special Populations

Genetic disease may occur with or without family history. Young onset, a strong ALS/FTD family history, unusual phenotype or ancestry-specific founder variant increases the likelihood of a genetic explanation, but testing should still be offered to all people with ALS with counselling.[4] Pregnancy, frailty and major comorbidity require individualized risk-benefit review of medicines, ventilation and procedures using current local labels and the patient’s goals; avoid blanket contraindications based on old reviews.[3]

Evidence, Guidelines & Regional Differences

• Global/current care framework: EAN 2024 integrates multidisciplinary, respiratory, nutritional, communication, symptomatic and palliative care.[3]
• UK: NICE NG42 provides the reader-visible UK pathway for MDT review, respiratory testing/NIV, cough assistance, gastrostomy and advance planning.[3]
• Riluzole: globally established, with a modest randomized-trial survival benefit and local-label monitoring.[5]
• Edaravone: FDA and PMDA authorization exists, including a US oral formulation; EAN 2024 does not recommend it outside trials in its setting.[3][6]
• Tofersen: FDA accelerated approval for SOD1-ALS and EU authorization under exceptional circumstances; the pivotal functional endpoint was negative and confirmatory evidence remains important.[7]
• AMX0035: market withdrawal in 2024 followed the negative PHOENIX trial; formal FDA approval withdrawal took effect in 2025. It is not current routine therapy (Federal Register).[3]

The mnemonic, and the mantra

The mantra: UMN plus LMN, sensation spared; riluzole early, NIV at FVC 50, gastrostomy before FVC falls, multidisciplinary clinic — and never miss multifocal motor neuropathy.[1][7]

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Advance care planning and palliative care

Begin sensitively and revisit at diagnosis and meaningful functional, respiratory, communication, feeding or caregiver transitions. Use supported decision-making; document preferences for NIV/invasive ventilation, CPR, gastrostomy, communication, place of care/death, proxy/advance directives and anticipatory symptom medicines according to local law.[3]

Palliative care runs alongside disease-modifying and supportive treatment. It addresses breathlessness, pain, anxiety, secretions, psychosocial and spiritual distress and caregiver bereavement. Decisions about invasive ventilation or withdrawal of ventilation require specialist planning, individualized comfort medication and family support; do not promise a fixed time to death after withdrawal.[3]

References

1. [1]Hardiman O, Al-Chalabi A, Chio A, Corr EM, Logroscino G, Robberecht W, Shaw PJ, Simmons Z, van den Berg LH Amyotrophic lateral sclerosis Nature Reviews Disease Primers, 2017.PMID 28980624
2. [2]Shefner JM, Al-Chalabi A, Baker MR, Cui LY, de Carvalho M, Eisen A, et al. A proposal for new diagnostic criteria for ALS Clinical Neurophysiology, 2020.PMID 32387049
3. [3]Van Damme P, Al-Chalabi A, Andersen PM, et al. European Academy of Neurology (EAN) guideline on the management of amyotrophic lateral sclerosis in collaboration with European Reference Network for Neuromuscular Diseases (ERN EURO-NMD) European Journal of Neurology, 2024.PMID 38470068
4. [4]Roggenbuck J, Eubank BHF, Wright J, et al. Evidence-based consensus guidelines for ALS genetic testing and counseling Annals of Clinical and Translational Neurology, 2023.PMID 37691292
5. [5]Miller RG, Mitchell JD, Moore DH Riluzole for amyotrophic lateral sclerosis (ALS)/motor neuron disease (MND) Cochrane Database of Systematic Reviews, 2012.PMID 22419278
6. [6]Writing Group, Edaravone (MCI-186) ALS 19 Study Group Safety and efficacy of edaravone in well defined patients with amyotrophic lateral sclerosis: a randomised, double-blind, placebo-controlled trial The Lancet Neurology, 2017.PMID 28522181
7. [7]Miller T, Cudkowicz M, Shaw PJ, et al. Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS New England Journal of Medicine, 2022.PMID 36129998
8. [8]Bourke SC, Tomlinson M, Williams TL, Bullock RE, Shaw PJ, Gibson GJ Effects of non-invasive ventilation on survival and quality of life in patients with amyotrophic lateral sclerosis: a randomised controlled trial The Lancet Neurology, 2006.PMID 16426990
9. [9]ProGas Study Group Gastrostomy in patients with amyotrophic lateral sclerosis (ProGas): a prospective cohort study The Lancet Neurology, 2015.PMID 26027943
10. [10]Cedarbaum JM, Stambler N, Malta E, et al. The ALSFRS-R: a revised ALS functional rating scale that incorporates assessments of respiratory function Journal of the Neurological Sciences, 1999.PMID 10540002
11. [11]Pender N, Pinto-Grau M, Hardiman O Cognitive and behavioural impairment in amyotrophic lateral sclerosis Current Opinion in Neurology, 2020.PMID 32833751
12. [12]Renton AE, Majounie E, Waite A, et al. A hexanucleotide repeat expansion in C9ORF72 is the cause of chromosome 9p21-linked ALS-FTD Neuron, 2011.PMID 21944779
13. [13]Neumann M, Sampathu DM, Kwong LK, Truax AC, Micsenyi MC, Chou TT, et al. Ubiquitinated TDP-43 in frontotemporal lobar degeneration and amyotrophic lateral sclerosis Science, 2006.PMID 17023659
14. [14]O'Driscoll BR, Howard LS, Earis J, Mak V BTS guideline for oxygen use in adults in healthcare and emergency settings Thorax, 2017.PMID 28507176