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Motor Neuron Disease

Motor neuron disease in adults generally commences between 30 and 60 years of age.


There is degeneration of the anterior horn cells in the spinal cord, the motor nuclei or the lower cranial nerves, and the corticospinal and corticobulbar pathways.


  1. Motor weakness
  2. No sensory loss or sphincter disturbance.
  3. Progressive course
  4. No identifiable underlying cause other than genetic basis in familial cases.



Five varieties have been distinguished on clinical grounds.

  1. Progressive bulbar palsy (LMN)
    Bulbar involvement predominates owing to disease pro­cesses affecting primarily the motor nuclei of the cranial nerves. LMN palsy of tongue, muscle of swallowing and facial muscle occurs.

    Other causes of bulbar palsy:
    1. GBS            
    2. Polio    
    3. Syringobulbia               
    4. Central pontine myelinosis
  2. Pseudobulbar Palsy (UMN)
    Bulbar involvement predominates in this variety also, but it is due to bilateral corticobulbar disease and thus reflects upper motor neuron dysfunction. Lesion is above mid pons (Cortico bulbar tract involvement) there is increase in jaw jerk, spastic tongue, Donald duck speech, emotional incontinence without mood change (Hollow laughter).

    Other causes of pseudobulbar palsy
    1. MS      
    2. Stroke
Important Points:

Abdominal reflexes are preserved in MND.


Extra Edge: Pseudo bulbar palsy does not occur in syringomyelia.

  1. Progressive Spinal Muscular Atrophy (LMN)
    This is characterized primarily by a lower motor neuron deficit in the limbs due to degeneration of the anterior horn cells in the spinal cord.
  2. Primary Lateral Sclerosis (UMN)
    There is a purely upper motor neuron deficit in the limbs
  3. Amyotrophic Lateral Sclerosis (UMN + LMN)
    Mixed upper and lower motor neuron deficit is found in the limbs. This disorder is sometimes associated with cognitive decline (in a pattern consistent with frontotemporal dementia) or parkinsonism.

Clinical Findings

  1. Symptoms and signs
    1. Difficulty in swallowing, chewing, coughing, breathing and talking (dysarthria) occur with bulbar involvement.
      In pro­gressive bulbar palsy, there is drooping of the palate; a depressed gag reflex; pooling of saliva in the pharynx; a weak cough; and a wasted, fasciculating tongue.
    2. In pseudobulbar palsy, the tongue is contracted and spastic and cannot be moved rapidly from side to side. Limb involvement is characterized by motor disturbances (weakness, stiffness, wasting, fasciculations) reflecting lower or upper motor neuron dysfunction; there are no objective changes on sensory examination, although there may be vague sensory complaints.
    3. The sphincters are generally spared.
    4. The disorder is progressive, and amyotrophic lateral sclerosis is usually fatal within 3-5 years; death usually result from pulmonary infections.
    5. Muscle cramps can occur (Ref. Hari. 18th ed., page - 2572)
    6. Sensation is normal and the cognitive functions are normal.

Causes of Exaggerated jaw jerk

  1. Multiple sclerosis
  2. Motor neuron disease
  3. Pseudobulbar palsy
  1. Laboratory and other studies
    1. Electromyography may show changes of chronic partial denervation, with abnormal spontaneous activity in the resting muscle and a reduction in the number of motor units under voluntary control.
    2. Motor conduction velocity is usually normal.
    3. Biopsy of a wasted muscle shows the histologic changes of denervation.
    4. The serum creatine kinase may be slightly elevated but never reaches the extremely high values seen in some of the muscular dystrophies.
    5. The CSF is normal.


  1. Riluzole (Ref. Hari. 18th ed., Pg- 3349), 50 mg orally twice daily, which reduces the presynaptic release of glutamate, may slow progression of amyotrophic lateral sclerosis.
  2. Other supported Treatment: Celecoxib, a cyclooxygenase-2 (COX-2) inhibitor, and pentoxifylline. Anticholinergic drugs (such as trihexyphenidyl, amitriptyline, or atropine).

Recent Advances:


Talampanel is a drug which is being investigated for the treatment of epilepsy, malignant gliomas and amyotrophic lateral sclerosis (ALS).  It is a noncompetitive antagonist of the AMPA receptor, a type of glutamate receptor in the CNS.

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