Amyotrophic Lateral Sclerosis
Amyotrophic lateral sclerosis (ALS) is the most common acquired motor neuron disease, characterized by progressive degeneration of both upper motor neurons (UMNs) and lower motor neurons (LMNs) in the brain, brainstem, and spinal cord. The disease follows a relentlessly progressive course with a median survival of 3–5 years from symptom onset, although phenotypic variants can confer a significantly different prognosis. Despite advances in genetics, diagnostics, and disease-modifying therapy, ALS remains a clinical diagnosis without a definitive biomarker, and no treatment can halt or reverse the disease.
Bottom Line
- Epidemiology: Global incidence of ~2 per 100,000/year with a male predominance (1.5:1); peak onset between ages 60–75 years; established risk factors include age, family history, and cigarette smoking
- Clinical presentation: Three most common phenotypes — lower limb onset, upper limb onset, and bulbar onset — each accounting for 25–30% of cases; up to 50% develop cognitive dysfunction and ~15% develop frontotemporal dementia
- Diagnosis: The Gold Coast criteria simplify diagnosis by requiring progressive motor impairment with UMN and LMN dysfunction in ≥1 body region (or LMN dysfunction in ≥2 regions), plus exclusion of other diseases; EMG is essential but a normal study does not exclude ALS
- Genetics: ~10% familial; C9orf72 is the most common monogenic cause (40% of familial ALS); pathogenic variants found in up to 15% of sporadic cases; testing increasingly recommended for all patients given emerging gene-based therapies
- Pathophysiology: Cytoplasmic TDP-43 aggregation in motor neurons in >90% of sporadic ALS; multiple molecular pathways involved including RNA processing, protein homeostasis, and glutamate excitotoxicity
- Disease-modifying therapies: Riluzole (glutamate inhibitor, ~3–6 month survival benefit), oral edaravone (free-radical scavenger), sodium phenylbutyrate–tauroursodeoxycholic acid (AMX0035), and tofersen (antisense oligonucleotide for SOD1 mutations)
- Supportive care: Noninvasive ventilation improves survival and quality of life; gastrostomy tube placement before FVC drops below 50%; multidisciplinary clinic care is associated with improved outcomes
Epidemiology
The global incidence of ALS is approximately 2 per 100,000 people per year, with a prevalence of roughly 5 per 100,000. Men are more commonly affected, with an incidence ratio of approximately 1.5 compared with women. ALS most commonly presents between the ages of 60 and 75 years, although onset can range from the second to beyond the ninth decade of life.
Risk Factors
| Risk Factor | Evidence |
|---|---|
| Age | Well-established; peak incidence 60–75 years |
| Family history | Well-established; ~10% familial; heritability estimated >50% in some sporadic ALS populations |
| Cigarette smoking | Well-established risk factor |
| Physical activity/concussion sports | Higher levels of physical activity and participation in concussion-associated sports reported to increase risk |
| Military service | Increased risk regardless of branch or timing of service |
| Heavy metals/pesticides | Possible risk factor; weaker evidence |
| Electromagnetic fields | Possible risk factor; weaker evidence |
Clinical Features
The motor manifestations of ALS are attributable to the loss of UMNs and LMNs in the brain, brainstem, and spinal cord. The presentation is heterogeneous, depending on where neuronal degeneration begins. Patients most commonly present with asymmetric lower limb weakness (~25–30%), asymmetric upper limb weakness (~25–30%), or bulbar manifestations (~25–30%). Less common initial presentations include respiratory weakness and head drop.
Limb Manifestations
Limb weakness typically begins distally. Patients with upper limb onset may initially report hand clumsiness, difficulty with buttons, or difficulty opening jars. In lower limb onset, foot drop is a common initial manifestation, with patients reporting frequent tripping or "foot slapping." These patients may initially be referred for evaluation of more common conditions such as carpal tunnel syndrome or lumbosacral radiculopathy. However, the absence of pain or sensory symptoms accompanying progressive weakness should alert the clinician to a more serious diagnosis.
With disease progression, weakness extends to proximal muscles. Upper arm and shoulder involvement interferes with overhead tasks such as dressing and hair washing, while hip and thigh weakness manifests with difficulty climbing stairs and rising from a seated position.
- LMN features: Muscle cramps (often painful and sleep-disruptive), fasciculations (profuse, visible on examination with proper exposure and indirect lighting), progressive weakness and atrophy
- UMN features: Spasticity (experienced as stiffness or slowness), hyperreflexia, Hoffmann sign or Tromner sign (often more reliable than plantar responses, which may be flexor or mute); UMN-predominant presentations often have less marked weakness on examination
Clinical Pearl: Fasciculations in ALS
Fasciculations should be assessed with the patient in a gown with arms, legs, shoulders, and upper chest exposed. With indirect lighting, observation for 30–60 seconds often reveals profuse fasciculations the patient may not have noticed. Importantly, ALS rarely presents with isolated fasciculations in the absence of weakness or other UMN/LMN findings. Isolated fasciculations are usually benign or attributable to another neurogenic process.
Bulbar Manifestations
Bulbar involvement is among the most distinctive presentations of ALS. Patients typically present with both dysarthria and dysphagia. In an adult with progressive mixed spastic-flaccid dysarthria, tongue atrophy and fasciculations, and no underlying structural abnormalities on imaging, the diagnosis can often be made rapidly.
- UMN bulbar features: Spastic dysarthria (slow, strained, often louder), slow and labored lingual movements, inability to protrude the tongue, laryngospasm (brief stridor with inspiratory difficulty), pseudobulbar affect (up to 30% of patients)
- LMN bulbar features: Flaccid dysarthria (hypernasal, quieter, breathy), weakness of lips, tongue, and palate, tongue atrophy with corrugated or "raisinlike" appearance, fasciculations (assess with tongue completely at rest)
- Pseudobulbar affect: Uncontrollable and intrusive bouts of laughing or crying, incongruent or excessive relative to the patient's emotional state; can be disruptive to patients and caregivers
Respiratory Manifestations
Weakness of the diaphragm and respiratory muscles results in exertional and resting dyspnea. Orthopnea is a characteristic feature, and diaphragmatic weakness may be unmasked when transitioning from upright to supine positioning. Patients may endorse excessive daytime sleepiness and morning headaches from sleep-disordered breathing. Expiratory muscle involvement leads to a weak cough and difficulty with secretion clearance. On examination, accessory muscle use, paradoxical breathing, and shortness of breath with speaking may be observed.
Cognitive Manifestations
Approximately 50% of patients with ALS will have some degree of cognitive or behavioral dysfunction on neuropsychological assessment, and about 15% will develop frontotemporal dementia (FTD). Co-occurrence of ALS and FTD portends a higher risk of an underlying genetic variation; patients with C9orf72 expansions have a 40–50% risk of cognitive impairment. Patients with ALS-FTD most commonly manifest behavioral features including disinhibition, apathy, and loss of empathy.
Case Vignette: ALS-FTD
A 52-year-old man presented with a 4-month history of progressive right upper limb weakness with hand clumsiness and subsequent forearm and biceps atrophy. His wife reported increasingly slurred speech and that he was "talking less and less." Examination revealed right upper limb atrophy and weakness (worse distally), fasciculations in all four limbs, mild spastic dysarthria, and decreased verbal fluency with impaired naming and repetition but preserved comprehension. EMG showed active and chronic denervation in the right upper limb and tongue. Over the following year, he became mute and developed left hand and right ankle weakness. He was diagnosed with ALS with frontotemporal dementia. Genetic testing for C9orf72, ATXN2, and a sequencing panel was negative.
Variant Presentations
Several well-described clinical variants exist within the ALS spectrum. These syndromes often do not satisfy formal diagnostic criteria because of preferential UMN or LMN involvement or restriction to one body region, but they are still acquired degenerative motor neuron diseases. Many will eventually evolve into a more characteristic ALS phenotype.
| Variant | Key Features | Prognosis |
|---|---|---|
| Primary lateral sclerosis (PLS) | Isolated UMN degeneration; bilateral lower limb spasticity and falls; spastic dysarthria; probable PLS at 2–4 years of isolated UMN involvement, definite PLS beyond 4 years | More favorable; longer course; some develop LMN features up to 10 years after onset |
| Progressive muscular atrophy (PMA) | Isolated LMN involvement; no UMN symptoms or signs; ~20% eventually develop UMN features; autopsy studies show UMN pathology | More prolonged survival than typical ALS |
| Flail arm syndrome | Bilateral, asymmetric LMN weakness and atrophy of both upper limbs; proximal onset common; EMG denervation restricted to cervical segments | Significant percentage survive >5 years |
| Flail leg syndrome | Bilateral, symmetric LMN weakness in the legs; distal onset typical; EMG denervation in lumbosacral segments | Significant percentage survive >5 years |
| Progressive bulbar palsy | Isolated bulbar onset with prominent dysphagia and dysarthria; may involve LMNs, UMNs, or both; majority evolve into typical ALS | Often aggressive; early gastrostomy tube consideration needed |
Case Vignette: Flail Leg Variant
A 77-year-old man presented with a 2-year history of bilateral leg weakness that began with right ankle weakness and tripping, progressing to marked atrophy and weakness in both lower limbs (grade 1–2/5). Upper limb reflexes were normal, lower limb reflexes were unobtainable, and the rest of the neurologic examination was unremarkable. EMG revealed active and chronic denervation confined to lumbosacral muscles with sparing of thoracic and arm segments. Weakness remained confined to the lower limbs for nearly 5 years before he developed hand weakness bilaterally, with interval development of cervical and thoracic denervation on EMG — illustrating the restricted clinical manifestations and protracted course of the flail leg variant.
Diagnosis
In the absence of a gold-standard test or biomarker, ALS continues to be primarily a clinical diagnosis. The clinician must recognize suggestive features while simultaneously excluding treatable mimics. The workup must be practical and tailored to the phenotype, ensuring a secure yet timely diagnosis. Through this process, the clinician should remain mindful of emerging respiratory or bulbar symptoms, treatment timelines, clinical trial eligibility, and the psychological burden of diagnostic uncertainty on patients and families.
Gold Coast Diagnostic Criteria
Gold Coast Criteria for ALS Diagnosis
All three of the following must be present:
- Progressive motor impairment documented by history or repeated clinical assessment, preceded by normal motor function
- UMN and LMN dysfunction in at least one body region (with both in the same region if only one region is involved) OR LMN dysfunction in at least two body regions
- Exclusion of other disease processes by appropriate investigations
Body regions: Bulbar, cervical, thoracic, and lumbosacral. LMN involvement in a region requires abnormalities in two limb muscles innervated by different roots and nerves, or one bulbar muscle, or one thoracic muscle (by clinical examination or EMG).
The Gold Coast criteria are simpler than the revised El Escorial and Awaji criteria, eliminate the definite/probable/possible classifications, and have increased sensitivity for detecting patients at earlier stages — facilitating earlier treatment initiation and clinical trial enrollment.
Electrodiagnostic Findings
EMG and nerve conduction studies should be performed in all patients with suspected motor neuron disease. Key findings include:
- Nerve conduction studies: Low-amplitude or absent compound muscle action potentials (CMAPs); sensory responses should be preserved
- Needle EMG: Active denervation (fibrillation potentials, positive sharp waves) and chronic denervation (large, long-duration motor unit potentials) in multiple myotomes spanning multiple body regions
- Fasciculation potentials: May be widespread and profuse, extending beyond the distribution of active denervation
Several caveats are important: incidental findings such as carpal tunnel syndrome or peripheral neuropathy are common and should not detract from ALS suspicion. EMG often evolves over time, and repeat testing may be indicated. Patients with UMN-dominant presentations may initially have a normal EMG, which does not exclude ALS.
Neuroimaging
MRI of the neuraxis is indicated in virtually all patients and should be guided by the clinical presentation. Brain MRI is typically most useful to exclude other diagnoses and is often unremarkable in ALS. However, T2 hyperintensity along descending corticospinal tracts may be seen, and susceptibility-weighted imaging (SWI) can reveal hypointensity in the precentral gyrus (the "motor band sign") in nearly 80% of patients.
Laboratory Workup
Routine blood work rarely changes the diagnosis but may be indicated based on phenotype. Many patients with ALS will have a mild-to-moderate creatine kinase elevation (often <1000 U/L). Additional targeted testing depends on the clinical scenario:
- LMN-dominant: Creatine kinase, West Nile virus serology, Lyme serology, anti-GM1 antibodies (for multifocal motor neuropathy, though elevated in >15% of ALS patients)
- Fatigability or ocular features: Acetylcholine receptor and MuSK antibodies, repetitive nerve stimulation
- UMN-dominant: Vitamin B12, vitamin E, copper levels; HIV, HTLV-I/II, syphilis, Lyme serologies; ANA and ENA panel; genetic testing for hereditary spastic paraparesis in chronic cases
Mimics and Diagnostic Pitfalls
ALS Mimics by Phenotype
- UMN-predominant mimics: Hereditary spastic paraparesis (sensory symptoms, bladder dysfunction, family history), nutritional deficiency myelopathy (B12, copper, vitamin E), adrenomyeloneuropathy (X-linked, sensory features, very long chain fatty acids), primary progressive MS, HTLV-I myelopathy
- LMN-predominant mimics: Multifocal motor neuropathy (peripheral nerve distribution weakness, conduction block, responds to IVIg), Kennedy disease (gynecomastia, perioral fasciculations, CK >1000 U/L, sensory involvement, CAG expansion), inclusion body myositis (finger flexor and quadriceps weakness), spinal muscular atrophy, post-polio syndrome, chronic inflammatory demyelinating polyradiculoneuropathy
- Combined UMN/LMN mimics: Cervical spondylotic myelopathy with polyradiculopathy (pain, sensory symptoms, bowel/bladder dysfunction), spinal dural arteriovenous fistula (abnormal flow voids, cord edema on MRI)
- Bulbar-onset mimics: Myasthenia gravis (ocular manifestations, fatigability), oculopharyngeal muscular dystrophy, multiple system atrophy (scanning dysarthria, ataxia), infiltrative tongue lesions (asymmetric unilateral atrophy — MRI of nasopharynx may be needed)
- Head drop mimics: Myasthenia gravis, inclusion body myositis, nemaline myopathy, multiple system atrophy (rigidity rather than true weakness)
Key principle: The presence of sensory symptoms, bowel/bladder dysfunction, or prominent pain should prompt investigation for alternative diagnoses. However, incidental sensory findings on EMG (e.g., from concomitant carpal tunnel syndrome) should not detract from ALS suspicion.
Genetics
Approximately 90% of patients are classified as sporadic ALS, with familial ALS accounting for at least 10% of cases (most autosomal dominant). However, pathogenic variations may be found in up to 15% of patients with sporadic disease. The heritability of ALS — the degree to which disease risk is attributable to genetic factors — has been estimated at greater than 50% in some sporadic populations, underscoring the complex interplay between genetic and environmental factors.
| Gene | Key Features |
|---|---|
| C9orf72 | Most common monogenic cause (~40% of familial ALS); hexanucleotide repeat expansion (GGGGCC); autosomal dominant with up to 100% penetrance by age 80; presents as ALS, FTD, or both; 40–50% risk of cognitive impairment; found in ~3% of sporadic ALS; can rarely be associated with parkinsonism, tremor, myoclonus, corticobasal syndrome |
| SOD1 | Second most common cause; discovered 1993; >200 variants identified; 90% penetrant by age 70; mediates disease through oxidative stress and inflammation; therapeutic target for tofersen |
| TARDBP | Encodes TDP-43 protein; discovered 2008; links genetic variation to the hallmark pathologic finding of cytoplasmic TDP-43 aggregation seen in >90% of sporadic ALS |
| FUS | RNA-binding protein; target for jacifusen (ION363) antisense oligonucleotide therapy currently in phase 3 trial |
| ATXN2 | Intermediate-length polyglutamine expansions increase ALS risk; therapeutic target for ION541 (BIIB105) antisense oligonucleotide in phase 1–2 trial |
Genetic Testing Recommendations
- Routinely offer: All patients with a family history of ALS or FTD; patients with ALS-FTD; patients younger than 50 years
- Consider broadly: All patients with ALS, given the frequency of pathogenic variants in sporadic disease and the ongoing development of gene-based therapies
- Asymptomatic relatives: May seek testing and genetic counseling for risk assessment and family planning
- Commercial laboratories now offer extensive panels covering common and rare genes, with some providing free or sponsored testing
Antisense Oligonucleotide Trials
| Target Gene | Medication | Trial Name | Phase |
|---|---|---|---|
| SOD1 | Tofersen (BIIB067) | VALOR | Post-approval (FDA-approved) |
| SOD1 (asymptomatic) | Tofersen (BIIB067) | ATLAS | Phase 3 |
| C9orf72 | IONIS-C9 (BIIB078) | 245AS101 | Phase 1 |
| C9orf72 | WVE-004 | FOCUS-C9 | Phase 1–2 |
| ATXN2 | ION541 (BIIB105) | 275AS101 | Phase 1–2 |
| FUS | Jacifusen (ION363) | ION363-CS1 | Phase 3 |
Pathophysiology
The pathophysiology of ALS involves a complex interplay of multiple molecular mechanisms. The rapid discovery of ALS-associated genes over the past 15 years has provided important insights, though our understanding remains incomplete.
- TDP-43 aggregation: Cytoplasmic TDP-43 inclusions are the hallmark pathologic finding in >90% of sporadic ALS; the discovery of TARDBP mutations directly linked genetic variation to this pathology
- RNA processing dysfunction: Multiple ALS-associated genes (TARDBP, FUS, C9orf72) encode proteins involved in RNA metabolism
- Protein homeostasis: Disruptions in protein stability, folding, and clearance mechanisms (including proteasomal and autophagic pathways)
- Glutamate excitotoxicity: Excessive glutamate signaling contributes to motor neuron death; the therapeutic target of riluzole
- Oxidative stress: SOD1 mutations are thought to cause disease through oxidative stress and inflammatory pathways; the therapeutic target of edaravone (free-radical scavenger)
- Cytoskeletal dysfunction: Impaired axonal transport and structural integrity of motor neurons
- Neuroinflammation: Microglial activation and inflammatory cascades contribute to disease progression
- Mitochondrial dysfunction: Impaired energy metabolism and increased oxidative stress
- C9orf72 mechanisms: Hexanucleotide repeat expansion causes disease through both toxic gain of function (RNA foci, dipeptide repeat protein aggregation) and loss of function
Disease-Modifying Therapies
Three disease-modifying medications are available for sporadic ALS, and one drug has been approved specifically for SOD1-associated ALS. All agents have a relatively modest effect on disease course. Patients should understand that the disease will continue to progress after treatment initiation.
Riluzole
An oral glutamate excitotoxicity inhibitor approved by the FDA more than 25 years ago. An initial placebo-controlled trial demonstrated a small but significant 12% increase in survival. Review of trial data revealed a median survival prolongation of ~3 months, while real-world evidence suggests even greater benefit (6–19 months). Dosed at 50 mg twice daily.
- Common adverse effects: Gastrointestinal discomfort, dizziness, elevated transaminases, fatigue
- Rare adverse effects: Neutropenia
- Monitoring: Liver function tests monthly for the first 3 months, then every 3 months
Edaravone (Oral Formulation)
A free-radical scavenger that modestly slows functional decline. An initial 24-week trial did not meet its primary endpoint, but a post hoc analysis identified benefit in patients with disease duration <2 years, preserved respiratory function (FVC ≥80%), and ALSFRS-R scores ≥2 on all items. A follow-up trial targeting this population showed a 33% reduction in ALSFRS-R decline. Oral edaravone was FDA-approved in May 2022 and can be administered via feeding tube.
- Dosing: Initial cycle: 105 mg daily for 14 days, then 14-day drug-free period. Subsequent cycles: 105 mg daily for 10 days within a 14-day period, then 14-day drug-free period
- Adverse effects: Gait disturbance, headaches
- Best evidence: Greatest benefit in patients earlier in disease course with preserved respiratory function
Sodium Phenylbutyrate–Tauroursodeoxycholic Acid (AMX0035)
An oral coformulation approved by the FDA in 2022 and conditionally approved in Canada. In a phase 2 trial, patients with definite ALS and symptom onset within 18 months experienced slower functional decline over 24 weeks. Subsequent analyses demonstrated a 4.8-month longer median survival compared with placebo, with treatment crossover-adjusted analyses suggesting an even greater survival benefit (6.9–10.6 months). A larger phase 3 trial (PHOENIX) has been initiated.
Tofersen (SOD1-Targeted Therapy)
An intrathecal antisense oligonucleotide (ASO) approved by the FDA via its accelerated approval pathway for patients with SOD1-associated ALS. In the phase 3 VALOR trial, tofersen did not significantly reduce ALSFRS-R decline at 28 weeks versus placebo, but it significantly reduced CSF SOD1 and neurofilament light chain levels. Extension studies are examining outcomes with earlier versus delayed initiation. The ATLAS trial is evaluating tofersen in clinically presymptomatic adults with confirmed SOD1 mutations.
Stem Cell Therapy
A phase 3 trial of intrathecal mesenchymal stem cell–neurotrophic factor cells did not meet its primary efficacy endpoint. However, improvements in CSF markers of inflammation and neurodegeneration were observed, and a subgroup of patients with milder disease (ALSFRS-R ≥35) showed a modest benefit. Research in this area continues.
Symptomatic and Supportive Care
Multidisciplinary care in specialized ALS clinics is essential and has been shown to improve survival and quality of life. American Academy of Neurology quality measures, updated in 2023, emphasize multidisciplinary care and now incorporate telemedicine options.
Respiratory Management
Patients should be screened early and frequently for respiratory muscle weakness. Symptom review and pulmonary function testing (FVC, slow vital capacity, or overnight oximetry) should be performed at diagnosis and every 3 months thereafter.
Noninvasive Ventilation (NIV) Initiation Criteria
- FVC <50% (AAN guideline) or <65% (Canadian Best Practice Recommendation)
- Sniff nasal inspiratory pressure (SNIP) worse than –40 cm H2O
- Maximum inspiratory pressure (MIP) worse than –60 cm H2O
- Orthopnea or abnormal nocturnal oximetry
- Daytime hypercapnia (PCO2 >45 mmHg)
NIV improves both survival and quality of life. Emerging evidence supports even earlier initiation. NIV should be started within 1 month of meeting criteria. Mechanical insufflation-exsufflation should be used when cough peak flow is <270 L/min.
With ongoing respiratory decline, invasive mechanical ventilation via tracheostomy can be considered. This intervention significantly prolongs survival but requires careful consideration of quality of life, personal values, and care burden. In North America, fewer than 5% of patients choose invasive ventilation, though rates vary significantly by country (up to 38% in Japan).
Bulbar Function and Nutrition
Weight loss occurs in more than 50% of patients due to dysphagia, weakness, atrophy, and hypermetabolism, and poor nutritional status predicts shorter survival. Dietary modification is the initial approach, but gastrostomy tube placement should be considered in any patient with significant weight loss or swallowing difficulty. Available evidence suggests gastrostomy can prolong survival.
Gastrostomy Timing
The discussion of gastrostomy tube placement should be introduced early to facilitate advance decision-making. Referral should occur when FVC is approaching 50%. While an FVC below 50% does not preclude placement, respiratory status should be closely monitored periprocedurally. NIV during the procedure may improve safety.
Symptom Management
| Symptom | Management Options |
|---|---|
| Sialorrhea | Sublingual atropine, amitriptyline, glycopyrrolate; botulinum toxin injections to salivary glands; radiation; scopolamine patch |
| Thick secretions | Mucolytics (acetylcysteine, guaifenesin/pseudoephedrine), cough augmentation, hydration |
| Laryngospasm | Lorazepam as needed, baclofen |
| Pseudobulbar affect | Dextromethorphan-quinidine, selective serotonin reuptake inhibitors (SSRIs) |
| Dysarthria/communication | Assistive communication devices, voice banking |
| Spasticity | Baclofen, tizanidine, botulinum toxin injections to affected muscle groups |
| Muscle cramps | Baclofen, mexiletine, levetiracetam, carbamazepine, phenytoin, stretching |
| Depression | SSRIs, psychiatry consultation |
| Weakness/functional decline | Bracing (e.g., ankle-foot orthotics), mobility aids including power wheelchair, home occupational therapy assessment |
Prognosis and Staging
Prognostication in ALS is challenging due to the wide variability in phenotypic presentation and rate of progression. Two staging systems are available but are not widely used in clinical practice:
- King's staging system: Four stages based on sequential involvement of body regions and the need for respiratory or swallowing support
- ALS Milano-Torino (MiToS) staging: Six stages (0–5) based on ALSFRS-R scores in four functional domains, with stage 5 indicating death
The Personalized ENCALS survival model provides individualized prognostic information using eight clinical predictors (age at onset, time to diagnosis, rate of ALSFRS-R progression, FVC, bulbar onset, definite El Escorial diagnosis, FTD, and C9orf72 expansion). This model categorizes patients into five survival groups ranging from very short (median 17.7 months) to very long (median 91.0 months). However, accurate individual prognostication remains a significant clinical challenge.
Prognostic Factors
- Shorter survival: Bulbar onset, older age at onset, rapid ALSFRS-R decline, low FVC at diagnosis, comorbid FTD, C9orf72 expansion
- Longer survival: Limb onset (especially flail arm/leg variants), younger age at onset, PLS or PMA phenotype, slower rate of progression
- Median survival: 3–5 years from symptom onset for typical ALS; significantly longer for variant presentations (PLS, PMA, flail limb variants)
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