Updated: 7/29/2020

Amyotrophic Lateral Sclerosis (ALS)

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Introduction
  • Also referred to as Lou Gehrig's disease.
  • A progressive motor neuron disorder characterized by involvement of anterior horn cells of spinal cord.
  • 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 fibrillationfasciculation 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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Questions (1)

(SBQ05UE.45) Which of the following investigative studies is most useful in the definitive diagnosis of Amyotrophic Lateral Sclerosis (ALS)? Review Topic | Tested Concept

QID: 1830
1

Genetic testing

6%

(208/3429)

2

MRI brain and spinal cord

22%

(739/3429)

3

Muscle biopsy

17%

(574/3429)

4

Serum protein electrophoresis and immunoelectrophoresis

5%

(180/3429)

5

Electrodiagnostic studies

50%

(1711/3429)

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