MOTOR NEURON DISEASE

Aetiology is unknown. There is loss of motor neurons and glimpis in motor, motor nuclei of brainstem and anterior horn of spinal cord, with degeneration of costicospinal  tract in spinal cord.

Classification

heriditary
1. Werdnig-Hoffmann disease(infantile spinal muscular atrophy).
2. Kugelberg- welander disease(adolescent spinal muscular atrophy)

sporadic
1.Amyotrophic lateral sclerosis
2. Progressive muscular atrophy.
3. Progressive bulbar palsy.
4. Primary lateral sclerosis.

Amyotrophic lateral sclerosis.
It is the most common form of progressive motor neuron disease. It is prime example of a neurodegenerative disease and is arguably the most devastating of the neurodegenerative disorder.

Pathology.
The pathologic hallmark of amyotropic lateral sclerosis is involvement of both upper and lower motor neurons.
The affected motor neurons undergo shrinkage wit accumulation of the pigment lipofuscin..Also there occurs proliferation of astroglia and microglia. In ALS, the motor neuron cytoskeleton is typically affected early in the illness..
 The death of peripheral motor neurons leads to denervation and consequent atrophy of the corresponding muscle fibre. This is basis for the term 'amyotrophy'. Loss of costical motor neurons results in thinning of the costicospinal tract.  This loss of fibres in tin lateral column and resulting fibrillary gliosis impart firmness. Hence the term lateral sclerosis.
The most remarkable feature is the selectivity of neuronck celll death. The entire sensory apparatus, the regulatory mechanism for the control and coordination of movement, and the components of the brain that are needed for cognitive processes, remain intact.
Thus motor neurons required for occular movili remains unaffected, as do the parasympathetic neurons in the sacral spinal cord that honesta the sphincters of bowel and bladder.

Clinical manifestations.
1. Weakness caused by denervation is associated with progressive wasting and atrophy of muscles, and particularly early in the illness, spontaneous twitching of motor units, or fasciculations.
2.In hands weakness is more in extensors as compared to flexors.
3. When initial involvement is that of bulbar neuron there is difficulty  with chewing, swallowing, and movements of tongue and face.
4. With prominent costicospinal involvement, there is hyperactivity of the tendon reflexes and spartia resistance to passive movements of affected limbs..
5. Degeneration of corticobulbar projections honesta the brainstem results in dysarthria and exaggeration of the motor expressions of emotion. This results in involuntsy excess in weeping or laughing.
6. Even in the late stages of the illnesss, sensory, bowel and bladder, and cognitive functions are preserved.

Diagnostic guidelines forALS by committe of the World Federation of Neurology.
Motor neurons of
1 bulbar
2. Cervical
3. Thoraccic
4. Lumbosacral
can be involved.
The disorder is termed 'definite' when three or four of above are involved.
Probable when two sites are involved.
Possible when only one site is affected.
Essential for the diagnosis is simultaneous involvement of upper and lower motor neuron.

Investigations
1. Spine radiology
2. EMG
3. Nerve conduction velocity.
4. MRI of spine.
5. Thyroid function test.
6. Lumbar puncture.

Differential diagnosis.
1 tumors in the cervical region or at foramen magnum.
2. Cervical spondylosis.
3.multifocal motor neuropathy with conduction block.

Treatment
1. No treatment arrest the underlying pathologic process in ALS.
2. Riluzole 100mg/d produces a modest lengthning of survival.
It is a sodium channel blocker that inhibits glutamate release.
3. Walking aids, respiratory support and physiotherapy are helpful.