Amyotrophic lateral sclerosis (ALS)

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• Amyotrophic Lateral Sclerosis (ALS) is a progressive, idiopathic, and fatal neurodegenerative disease of the human motor system.
• Pathology of the Upper and Lower Motor Neurons: This disease process causes rapidly progressive muscle atrophy and weakness resulting from the degeneration of both upper motor neurons (UMNs) and lower motor neurons (LMNs). At the neuropathological level, there is a prominent loss of Betz cells from the motor cortex with secondary degeneration of the corticospinal and spinocerebellar tracts. In the peripheral nervous system, the primary pathology is a neuronopathy of the anterior horn cells of the spinal cord. Because the anterior horn cells are located proximal to the point where motor and sensory fibers merge, the signs and symptoms of this motor neuron disease are purely motor.
• Cellular and Genetic Underpinnings: The disease has a genetic component, with at least 13 genes and loci associated with ALS. Inclusions in the TAR DNA-binding protein-43 (TDP-43) have been identified as key histopathological features in both ALS and frontotemporal dementia. Additionally, both motor and sensory peripheral nerves undergo axonal degeneration, segmental demyelination, and motor end plate and axon terminal involvement. This progressive denervation impairs skeletal, ocular, bulbar, and respiratory muscle groups, ultimately leading to terminal respiratory complications.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Airway and Breathing Stabilization: Assess the airway immediately. Keep the patient positioned upright (at a 90° angle) to optimize diaphragmatic excursion, reduce aspiration risk, and prevent carbon dioxide retention. If the patient exhibits poor oxygenation, cyanosis, confusion, or a deteriorating level of consciousness, endotracheal intubation is indicated.
• Oxygenation and Ventilatory Support: Avoid administering supplemental oxygen alone, as it can blunt the hypoxic respiratory drive and worsen CO2 retention. Provide oxygen combined with non-invasive ventilation, specifically Bilevel Positive Airway Pressure (BiPAP), to manage a tenuous respiratory status. If the patient is in acute respiratory distress, promptly consult respiratory therapy.
• Assessing Respiratory Reserves: Actively evaluate diaphragmatic and respiratory muscle weakness by measuring Forced Vital Capacity (FVC) and Negative Inspiratory Force (NIF). A history of FVC <50% predicted in an acute patient in respiratory distress is poorly prognostic. A measured FVC <15 mL/kg or an NIF less negative than -15 mm H2O indicates a high risk of impending ventilatory failure and the need for mechanical support. A poor or absent cough, or the inability to blow up the cheeks with air, indicates a high risk of immediate respiratory compromise.
• Rapid Sequence Intubation (RSI) Regimen:
• Preoxygenation: Ensure appropriate preoxygenation, ideally utilizing BiPAP, as these patients have a decreased ability to oxygenate once sedated.
• Paralytic Choice (Strict Exclusion): Succinylcholine is absolutely contraindicated and must be avoided. Its use can exacerbate symptoms and trigger catastrophic hyperkalemia due to extrajunctional acetylcholine receptor upregulation following progressive muscle denervation of more than a 3-day duration.
• Preferred Paralytic: Administer Rocuronium at 0.6 to 1.5 mg/kg IV/IO slow push as the preferred induction agent.
• Circulation and Support: Evaluate for hypotension, tachycardia, or other signs of shock, treating with IV fluids, vasopressors, or antibiotics if sepsis or aspiration pneumonia is suspected. Use nebulized saline and suction to manage thick bronchial secretions, and employ assisted cough with physiotherapy.
• The Goals of Care Rule: Always assess and confirm the patient's code status, advanced directives, or living will prior to sedation and intubation if clinically feasible, as tracheostomy is frequently required for eventual extubation.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Top 5 "Can't-Miss" Mimics:

    1.  **Acute Stroke (Anterior or Brainstem):** Presents with sudden-onset focal motor deficits or bulbar signs (dysarthria, dysphagia) but lacks chronic progressive UMN/LMN mixed signs.
    2.  **Myasthenia Gravis (MG):** Presents with fatigable skeletal muscle weakness, particularly ocular and bulbar, but lacks UMN signs (normal reflexes) and features fluctuating ocular deficits like ptosis or diplopia which are typically spared in ALS.
    3.  **Multiple Sclerosis (MS):** A progressive demyelinating CNS disease featuring visual loss, sensory paresthesias, and a relapsing-remitting course, but lacks LMN signs like muscle fasciculations and atrophy.
    4.  **Guillain-Barré Syndrome (GBS):** Presents with rapid, symmetrical, ascending flaccid paralysis and areflexia, but typically features antecedent infections (e.g., *Campylobacter jejuni*) and sensory paresthesias.
    5.  **Polymyositis / Inflammatory Myositis:** Presents with proximal muscle weakness, tenderness, and marked CPK elevation, but lacks upper motor neuron signs.

• Prioritized Diagnostic Workup Strategy:
• Arterial Blood Gas (ABG): Obtain an arterial blood gas (ABG) to evaluate hypoxia, hypercarbia, or respiratory acidosis associated with diaphragmatic dysfunction. Note: Blood gases are often unhelpful early and may remain normal until severe failure develops.
• Creatine Phosphokinase (CPK/CK): Order Creatine Phosphokinase (CPK/CK), as it may be significantly elevated in ALS, helping differentiate it from other neuropathies, or ruling in inflammatory myositis/rhabdomyolysis.
• Standard Stroke and Infection Lab Panel: Send a standard laboratory panel including CBC (to check for anemia or leukocytosis), CMP (to check electrolytes, renal, and hepatic function), and Urinalysis (to rule out occult urinary tract infections as a trigger for weakness).
• Lyme Serology: Lyme Serology is indicated if there is a known history of tick exposure or clinical suspicion.
• Cerebrospinal Fluid (CSF) Studies: Cerebrospinal Fluid (CSF) Studies are indicated if there is concern for meningitis, encephalitis, or GBS.
• Brain and Spinal Cord MRI: Perform brain and spinal cord MRI to rule out structural compressive lesions like compressive radiculopathy, spinal tumors, or epidural abscesses.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• Standard ECG Checklist:
• Rule Out Concomitant Arrhythmias: Rule out concomitant arrhythmias with a standard ECG, as new-onset cardiac abnormalities can cause generalized weakness.
• Chest Radiography (CXR) Checklist:
• Aspiration Pneumonia & Atelectasis: Order a Chest Radiograph (CXR) to look for focal infiltrates, consolidation, or volume loss, as ALS patients with bulbar weakness are at extremely high risk for aspiration pneumonia or atelectasis.
• Cranial and Spine CT Checklist:
• Head CT: A Head CT is essential in the undifferentiated patient presenting with acute bulbar signs or cognitive deficits to rule out intracranial masses, hemorrhage, or acute stroke.
• Magnetic Resonance Imaging (MRI) Sequence Checklist:
• Corticospinal Tract Hyperintensity: On brain and spinal cord MRI, look for the classic T2-hyperintensity along the motor tracts (specifically the corticospinal tracts).
• Frontal Cortical Atrophy: Assess for frontal cortical atrophy, which is associated with advanced cognitive involvement and frontotemporal dementia.
• Exclusion of Compressive Lesions: The primary role of MRI in the emergency setting is to exclude other ongoing compressive lesions or spinal pathology, as initial MRI findings in early ALS can be normal.
• Electromyography (EMG) Visual Checklist (Outpatient):
• Widespread Denervation: Electromyography (EMG) visual checklist (typically completed in the outpatient setting) will show widespread active denervation and chronic reinnervation in multiple nerve roots or anterior horn territories.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• El Escorial, Awaji, and Gold Coast Criteria: El Escorial, Awaji, and Gold Coast criteria are three commonly used tools to aid in the clinical diagnosis of ALS. These criteria require the standardized demonstration of concurrent mixed upper and lower motor neuron signs in similar anatomical distributions with progressive spread.
• Amyotrophic Lateral Sclerosis Functional Rating Scale (revised): The Amyotrophic Lateral Sclerosis Functional Rating Scale (revised) is a sensitive and reliable tool used to quantitatively score the patient's functional status and track disease progression.
• Palliative Prognostic Score (PPS): The Palliative Prognostic Score (PPS) is a validated scoring system ranging from 100% to 0% based on ambulation, self-care, intake, and consciousness. A patient with reduced oral intake and a diminished GCS score can have a Palliative Prognostic Score of 10%, indicating a 1-week expected median survival.
• GO-FAR (Global Outcome After Cardiac Arrest) Score: The GO-FAR (Global Outcome After Cardiac Arrest) score is a validated clinical tool incorporating age, comorbidities, and laboratory values to predict neurologically intact survival following cardiac arrest. A calculated GO-FAR score of 25 or higher translates to a less than 1% chance of survival with minimal neurologic disability, which can inform shared decision-making regarding code status.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The "Reassured by Normal Blood Gas" Trap: Failing to recognize impending diaphragmatic fatigue because the early blood gas appears normal. In neuromuscular weakness, blood gases are notoriously unhelpful early, and hypercarbia/hypoxia are late, pre-terminal findings.
• The "Supp-O2 Alone" Disaster: Administering supplemental oxygen therapy alone to a dyspneic ALS patient. This blunts the hypoxic drive, worsening hypercapnic respiratory failure and carbon dioxide retention; oxygen must be delivered via non-invasive positive pressure (BiPAP).
• The Succinylcholine Hyperkalemia Catastrophe: Administering succinylcholine for intubation in an ALS patient. Upregulation of extrajunctional acetylcholine receptors from progressive lower motor neuron denervation leads to massive intracellular potassium efflux and fatal cardiac arrest.
• The "Unplanned Intubation" Trap: Intubating a crashing ALS patient without reviewing goals of care or checking for a POLST/DNR order. Because diaphragmatic weakness in ALS is progressive and irreversible, these patients are almost impossible to extubate and typically require a permanent tracheostomy—an outcome many have explicitly documented they wish to avoid.
• Mandatory Critical Actions:
• Perform bedside NIF and FVC testing immediately in any ALS patient with a respiratory complaint, and trend these numbers hourly.
• Place the patient strictly upright (90°) to mechanical advantage the diaphragm and prevent aspiration of oral secretions.
• Confirm goals of care and code status immediately upon ED arrival for any patient with known ALS presenting in distress.
• Utilize Rocuronium as the paralytic agent of choice during intubation.

7. MCQ MASTERCLASS (Written Exam Tips)

• Mixed upper and lower motor neuron signs with no sensory loss is pathognomonic for ALS.
• "The Split Hand Phenomenon": The 'Split Hand Phenomenon' is a classic high-yield physical finding in ALS characterized by profound wasting/atrophy of the thenar group with relative sparing of the hypothenar group.
• T2-Hyperintensity of the Motor Tracts: While Dawson fingers on MRI indicate MS, T2-hyperintensity within the motor tracts (specifically the corticospinal tracts) on brain and spine MRI is a classic radiologic indicator of ALS.
• Pathology Localization: Anterior horn cell neuronopathy localizes the lower motor neuron pathology. Betz cell degeneration in the motor cortex localizes the upper motor neuron pathology.
• Inclusion Aggregates: TDP-43 basophilic inclusions represent the pathognomonic protein aggregate identified in motor neurons in ALS and associated frontotemporal dementia.
• Approved Disease-Modifying Agents:
• Riluzole: Riluzole is a preferential tetrodotoxin sodium channel blocker that modulates excitotoxic glutamate. It is one of the only approved disease-modifying agents and has been shown to prolong survival or time to ventilator-dependence by 2 to 3 months.
• Edaravone: Edaravone is an antioxidant that slows the decline in physical and respiratory function.
• Tofersen: Tofersen is an antisense oligonucleotide approved exclusively for patients with superoxide dismutase-1 (SOD1) gene mutations.
• Distractor Differentiation:
• Myasthenia Gravis: Myasthenia Gravis features fatigable weakness and ptosis/diplopia, but lacks UMN signs and has no muscle wasting or fasciculations.
• Guillain-Barré Syndrome: GBS presents with ascending flaccid paralysis with areflexia, but always features sensory paresthesias (which are absent in ALS) and demonstrates albuminocytologic dissociation on LP.
• PLS vs. PMA: Primary Lateral Sclerosis (PLS) is characterized by progressive upper motor neuron signs only, whereas Progressive Muscular Atrophy (PMA) is characterized by progressive lower motor neuron signs only.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• Initial Triage and Code Activation: "Initial Triage and Code Activation: 'As soon as this patient arrives, I am activating our respiratory therapy team and setting up a bedside airway cart. I will place the patient strictly upright at 90° to optimize diaphragmatic excursion and reduce the risk of carbon dioxide retention and aspiration.'"
• First 10-Minute Interventions: "First 10-Minute Interventions: 'My immediate diagnostic actions are to perform an emergent point-of-care capillary glucose, check a baseline venous or arterial blood gas to evaluate for respiratory acidosis, and obtain a bedside negative inspiratory force (NIF) and forced vital capacity (FVC). I will apply non-invasive positive pressure ventilation (BiPAP) if the NIF is less negative than -15 to -20 cm H2O or if the FVC is less than 15 mL/kg.'"
• Addressing Goals of Care: "Addressing Goals of Care (Critical Oral Board Point): 'Before proceeding with any advanced airway intervention, I will immediately review the patient's records for an advanced directive, POLST, or living will, and consult with the family or surrogate decision-maker. I will discuss that endotracheal intubation in progressive ALS carries a very high likelihood of requiring a permanent tracheostomy for extubation.'"
• RSI Execution: "RSI Execution: 'If the patient is unstable and we must intubate, I will perform a rapid sequence intubation. I will administer Rocuronium at 1.2 mg/kg IV as our paralytic agent. I will explicitly state to my team that Succinylcholine is strictly contraindicated due to the risk of catastrophic hyperkalemia from extrajunctional receptor upregulation.'"
• Post-Intubation and Disposition: "Post-Intubation and Disposition: 'I will order a chest radiograph to evaluate for aspiration pneumonia, confirm correct tube placement with continuous waveform capnography, and admit this patient to the intensive care unit (ICU) for close monitoring.'"