Amyotrophic Lateral Sclerosis

🧠 Standard of Care & Symptoms

Amyotrophic Lateral Sclerosis (ALS), commonly referred to as Lou Gehrig's disease, is a progressive, fatal neurodegenerative disorder selectively targeting motor neurons.

• Presentation: Progressive muscle weakness and denervation.
  • LMN Signs: Muscle atrophy, weakness, and **fasciculations** (visible muscle twitching), starting distally (limb onset) or in bulbar muscles.
  • UMN Signs: Spasticity, hyperreflexia (hyperactive reflexes), and positive Babinski sign due to corticospinal tract degeneration.
  • Bulbar Symptoms: Dysarthria (difficulty speaking), dysphagia (difficulty swallowing), and emotional lability (pseudobulbar affect). Progresses to respiratory muscle weakness.
• Etiology: Driven by the simultaneous degeneration of upper motor neurons in the primary motor cortex and lower motor neurons in the brainstem and anterior horns of the spinal cord.

🧬 Diagnostics & TDP-43 Pathology

Diagnosis is established clinically, supported by electrophysiology and genetic screening.

• Electromyography (EMG): Demonstrates widespread active denervation (fibrillation potentials, positive sharp waves) and chronic reinnervation (large, polyphasic motor unit potentials) across multiple spinal and bulbar segments.
• Neuroimaging (MRI): Essential to exclude structural mimics like cervical spondylotic myelopathy or Syringomyelia.

EAAT2 Loss, TDP-43 Aggregates, & C9orf72 Repeats

The molecular pathophysiology of motor neuron death involves distinct genetic mutations and glial transport failure:

• Astrocytic Glutamate Excitotoxicity: A key mechanism of damage is the downregulation of the astrocytic glutamate transporter **EAAT2** (excitatory amino acid transporter 2) in the motor cortex and spinal cord. This leads to prolonged synaptic glutamate presence, causing chronic calcium influx and mitochondrial damage in postsynaptic motor neurons.
• TDP-43 Aggregation: Over 95% of ALS cases exhibit cytoplasmic inclusion bodies containing abnormally phosphorylated and ubiquitinated **TDP-43** (transactive response DNA-binding protein 43). This represents a loss of normal nuclear RNA-binding function and gain of cytoplasmic toxicity.
• Genetic Mutations: Approximately 10% of cases are familial. The most common genetic cause is a hexanucleotide (GGGGCC) repeat expansion in the **C9orf72** gene, followed by mutations in **SOD1** (superoxide dismutase 1), which leads to misfolded protein toxicity.

💊 Disease-Modifying Pharmacotherapy

Management involves disease-modifying agents to slow progression, paired with proactive multidisciplinary symptom care.

Disease-Modifying Therapy

• Riluzole (Rilutek): An oral agent that inhibits glutamate release and blocks voltage-gated sodium channels. Clinically proven to extend survival by approximately 2 to 3 months. Requires regular monitoring of liver enzymes.
• Edaravone (Radicava): An intravenous or oral free radical scavenger that reduces oxidative stress on motor neurons. Slows functional decline in select early-stage patients.
• Tofersen (Qalsody): An antisense oligonucleotide indicated specifically for patients with SOD1-mutated ALS. Administered intrathecally.

Symptomatic Support

• Spasticity Management: Baclofen or Tizanidine are used to reduce muscle tightness.
• Respiratory and Nutritional Support: Early non-invasive ventilation (NIV/BiPAP) slows decline and improves quality of life. Percutaneous endoscopic gastrostomy (PEG) is indicated for severe dysphagia to maintain caloric intake.

🔬 Active Clinical Trials

Clinical trials are currently evaluating antisense oligonucleotides targeting C9orf72 transcripts, anti-inflammatory immunotherapies, and stem cell transplantation to promote motor neuron survival.

🗺️ Next Steps After Diagnosis

If you or a loved one have recently been diagnosed with ALS, implement these care steps:

1. Establish Care with an ALS Center: Consult a multidisciplinary clinic that coordinates neurology, pulmonology, physical therapy, speech therapy, and nutrition in one visit.
2. Initiate Riluzole: Discuss starting oral Riluzole, obtaining baseline liver function panels before starting.
3. Arrange Genetic Counseling: Discuss testing for C9orf72 and SOD1 gene mutations to determine family risk and check eligibility for targeted therapies like Tofersen.
4. Obtain Baseline Pulmonary Function: Perform baseline FVC testing to monitor respiratory muscle strength and determine when to start BiPAP.

❓ Patient FAQ

Q: Does ALS affect thinking and memory?
A: Historically, ALS was thought to only affect motor systems. However, up to 50% of patients experience some cognitive changes. Approximately 15% develop a specific form of dementia called **frontotemporal lobar degeneration (FTLD)**, which is genetically linked to the C9orf72 mutation. This can manifest as changes in behavior, personality, or language.

Q: What causes the muscle twitching (fasciculations) in ALS?
A: Fasciculations are involuntary, minor twitches of muscle fibers. They occur because the lower motor neurons in the spinal cord are degenerating. As these nerves lose their connection to the muscles, the muscle fibers become hyper-irritable and fire spontaneously. While twitches are common, they are diagnostic for ALS only when accompanied by progressive muscle weakness and atrophy.