ALS: The Science Behind Motor Neuron Disease and Current Research

The Paradox of Stephen Hawking: A 50-Year Survival in a 2–5 Year Disease

Amyotrophic lateral sclerosis (ALS) carries one of the starkest prognoses in neurology: median survival of 2–5 years from symptom onset, with approximately 50% of patients dying within 3 years of diagnosis. Stephen Hawking, diagnosed in 1963 at age 21 and surviving until 2018, was a profound outlier — his survival was attributed to a particularly slow-progressing form of familial ALS, assisted by early access to advanced respiratory support. His case is statistically extraordinary. For the 30,000 Americans living with ALS at any given time and the 5,000 newly diagnosed each year, the disease follows a relentless trajectory: progressive paralysis, respiratory failure, and death, typically while cognition remains largely intact.

ALS is classified as a motor neuron disease — a category that also includes primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), and progressive bulbar palsy (PBP). ALS is distinguished by involvement of both upper motor neurons (UMN) originating in the motor cortex and lower motor neurons (LMN) in the brainstem and spinal cord. This dual involvement produces a unique clinical signature.

Upper vs. Lower Motor Neuron Signs: The Diagnostic Fingerprint

Distinguishing UMN from LMN involvement requires examination skills that are central to the neurology of ALS. Their simultaneous presence in the same patient is the clinical hallmark that raises suspicion for ALS.

• Upper motor neuron signs: Spasticity (increased muscle tone), hyperreflexia (exaggerated deep tendon reflexes), pathological reflexes (Babinski sign: upgoing toe on plantar stimulation), slowness of voluntary movement, and pseudobulbar affect (inappropriate laughing or crying from corticobulbar tract involvement)
• Lower motor neuron signs: Weakness, muscle atrophy (wasting), fasciculations (spontaneous muscle twitching visible under the skin), hyporeflexia (diminished deep tendon reflexes), and hypotonia (decreased muscle tone)

The presence of both hyperreflexia (UMN) and fasciculations with atrophy (LMN) in the same muscle group is a red flag for ALS that should prompt urgent neurological referral. Most other diseases produce either UMN or LMN signs, not both simultaneously.

El Escorial Diagnostic Criteria

The El Escorial criteria, first published in 1994 and revised in the Awaji-Shima criteria (2008), provide the diagnostic framework for ALS. The Awaji criteria use EMG evidence as equivalent to clinical signs, improving sensitivity particularly in bulbar-onset ALS. The diagnostic levels reflect the certainty of diagnosis:

• Definite ALS: UMN and LMN signs in three or more regions (bulbar, cervical, thoracic, lumbosacral)
• Probable ALS: UMN and LMN signs in two regions, with some UMN signs rostral to LMN signs
• Possible ALS: UMN and LMN signs in one region, or UMN signs in two or more regions
• Suspected ALS: LMN signs only in two or more regions

The average time from symptom onset to diagnosis is 10–16 months — a delay largely attributable to the disease's initial presentation mimicking more common conditions (cervical myelopathy, multifocal motor neuropathy, Kennedy's disease) and the requirement to exclude these alternatives before confirming ALS. Diagnostic delay is one of ALS's most significant unresolved problems.

Genetic Architecture: SOD1, C9orf72, FUS, and TARDBP

Approximately 10% of ALS cases are familial (FALS), with identifiable inherited mutations; 90% are sporadic (SALS), though genetic factors contribute even in sporadic disease.

The C9orf72 repeat expansion — discovered in 2011 — was a landmark finding, explaining a large proportion of previously unresolved familial ALS and also linking ALS to frontotemporal dementia (FTD). Approximately 15% of ALS patients have clinically significant cognitive impairment, and the ALS-FTD spectrum is now recognized as a continuum sharing genetic and pathological features.

Treatment: Riluzole, Edaravone, and the Modest Frontier

Riluzole (Rilutek), approved by the FDA in 1995, remains the only ALS drug with well-replicated evidence of survival benefit. It inhibits glutamate neurotransmission by blocking voltage-gated sodium channels and glutamate release, reducing excitotoxic neuronal death. Clinical trial evidence shows riluzole extends median survival by approximately 2–3 months — statistically significant but clinically modest. Despite this modest effect, riluzole is standard of care, with good tolerability and low cost after patent expiration. The numbers are not impressive, but they are real.

Edaravone (Radicava), a free radical scavenger approved by the FDA in 2017, demonstrated benefit in a Japanese trial showing a 33% slowing of functional decline over 24 weeks in a specific patient subgroup (early disease, homogeneous functional scores). Subsequent real-world studies outside Japan have not consistently replicated this finding, and the European Medicines Agency declined approval. Edaravone's role remains contested.

Tofersen: The Antisense Oligonucleotide Era Begins

Tofersen (Qalsody), approved by the FDA in April 2023 for ALS patients with SOD1 mutations, represents the first precision medicine approach to the disease. Tofersen is an antisense oligonucleotide (ASO) — a synthetic RNA strand that binds to SOD1 messenger RNA and triggers its degradation, reducing production of the misfolded SOD1 protein responsible for motor neuron death in this genetic subtype.

In the VALOR trial, tofersen did not meet its primary endpoint of functional decline slowing after 28 weeks. However, CSF SOD1 protein was reduced by approximately 38%, and secondary and exploratory biomarker endpoints showed significant benefit, particularly in slower-progressing patients. A longer-term open-label extension study suggested survival benefit. The FDA granted accelerated approval based on the SOD1 biomarker reduction, reasoning it is reasonably likely to predict clinical benefit. Tofersen is administered by intrathecal injection every four weeks after loading doses. It is the template for a new generation of gene-silencing approaches targeting C9orf72, TDP-43, and other ALS-associated mutations currently in clinical trials.

Ice Bucket Challenge: Research Impact by the Numbers

The ALS Ice Bucket Challenge, which spread virally across social media in the summer of 2014, raised $115 million for the ALS Association in an eight-week period — compared to $2.7 million in the same period the previous year. The funds directly supported research that led to the identification of NEK1 as a significant ALS risk gene (2016), contributed to Project MinE — an international genome-wide sequencing project — and supported early-stage tofersen research. Without the Ice Bucket Challenge, the ALS research pipeline of 2023 would be meaningfully thinner. A social media phenomenon produced genuinely accelerated science. That outcome was not guaranteed.

Feeding Tubes and Ventilation: The Decisions That Define ALS Care

As ALS progresses, bulbar weakness (affecting swallowing) and respiratory muscle weakness (reducing forced vital capacity, FVC) create critical decision points. Percutaneous endoscopic gastrostomy (PEG) feeding tube placement is recommended when dysphagia causes significant weight loss or aspiration risk, preferably when FVC is still above 50% — the threshold below which procedural risk increases substantially. Non-invasive ventilation (NIV/BiPAP) is recommended when FVC falls below 50% or respiratory symptoms emerge; NIV extends survival by a median of 7–11 months and improves quality of life. Invasive mechanical ventilation via tracheostomy is used by approximately 5% of ALS patients who choose total respiratory support. These are not simply medical decisions — they are deeply personal choices about how to live with a disease that offers no cure.