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Updated: Jun 18 2021

Amyotrophic Lateral Sclerosis (ALS)

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  • summary
    • Amyotrophic Lateral Sclerosis, also referred to as Lou Gehrig's disease, is a progressive motor neuron disorder caused by degeneration of the anterior horn cells of the spinal cord. Patients present with progressive weakness and spasticity leading to impaired breathing, swallowing, and ambulation.
    • Diagnosis is dependent on demonstration of both upper and lower motor neuron involvement in the same extremity in the absence of pain or sensory symptoms. Nerve conduction studies will show widespread denervation and reinnervation. There are currently no laboratory tests that confirm the diagnosis.
    • Treatment is currently focused on maintenance of function and comfort. Currently, there is no cure for the condition.
  • Etiology
    • Pathologic features
      • lower motor neuron signs
        • loss of motor neurons within the anterior horns of the spinal cord and motor cranial nerve nuclei
      • upper motor neuron signs
        • degeneration with loss of myelinating fibers in the corticospinal and corticobulbar pathways
      • abnormal motor conduction, normal sensory conduction
    • Genetics
      • cause is mostly unknown
      • small percentage (~5%) of patients have familial form of the disease
        • some map to gene for superoxide dismutase on chromosome 21
  • Presentation
    • Symptoms
      • painless weakness in one extremity that extends to the other extremities
      • fasciculations
      • impaired speech or swallowing
      • reduced head control
      • breathing difficulty
      • muscle cramping
      • urinary frequency or incontinence (late findings)
      • sensory remains normal
    • Physical exam
      • neck ptosis (neck drop) due to neck extensor weakness
      • manual muscle testing elicits muscle cramping
      • upper motor neuron (UMN) signs
        • spasticity
        • hyperreflexia
        • (+) Hoffman's
        • (+) Babinski's
        • spastic dysarthria
      • lower motor neuron (LMN) signs
        • muscular atrophy
        • weakness
        • clinical fasciculations
        • clumsiness
  • Evaluation
    • Diagnosis
      • dependent on demonstration of both UMN and LMN involvement
      • combination of UMN and LMN in the same extremity, in the absence of pain or sensory symptoms, and cranial nerve findings is highly indicative of ALS
      • often misdiagnosed as cervical myelopathy or radiculopathy
    • Laboratory diagnosis
      • there are currently no laboratory tests that confirm the diagnosis
    • EMG / NCS - shows denervation + reinnervation
      • widespread decreased amplitude of CMAP and slowed motor conduction velocity
      • denervation (fibrillations and positive waves) + decreased recruitment in ≥ 3 extremities
      • reinnervation
      • abnormal spontaneous fibrillation & fasciculation potentials
      • normal sensory studies (SNAP, sensory nerve action potentials)
  • Differentials
    • Peripheral compressive neuropathy
      • hyperreflexia and other UMN signs (Babinski, Hoffman) are present in ALS (which can present in a single extremity mimicking cubital/carpal tunnel syndrome), but absent in peripheral neuropathy
      • ALS has normal sensory studies on EMG/NCS
  • Treatment
    • Nonoperative
      • currently no cure or effective treatment
        • goals of treatment
          • provide supportive care
          • prevent progression
          • maintain independent patient function and comfort
      • riluzole
        • indications
          • modest benefits only
          • prolongs life by 2-3 months
        • mechanism
          • blocks tetrodotoxin-sensitive sodium channels associated with damaged neurons
          • delays onset of ventilator-dependence and may prolong survival
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