Motor Neuron Diseases for NEET PG / FMGE:

Content: MOTOR NEURON DISEASE – FOR NEET PG/FMGE

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Definition:

It is the disease of motor neurons.
It is an irreversible loss of motor neurons and gliosis; in motor cortex, motor nuclei of brainstem and anterior horn of spinal cord.

It can affect any age but most patients are over 40 years old at the time of diagnosis.

90% MNDs are sporadic in nature.

There won’t be any sensory involvement.

Nomenclature:

  1.    UMN lesion of Cortico-bulbar tract: Pseudo Bulbar Palsy.

  2.    LMN lesion Cortico-bulbar tract: Progressive Bulbar Palsy.

  3.    UMN lesion of corticospinal tract: Primary Lateral Sclerosis.

  4.    LMN lesion of corticospinal tract: Progressive Spinal Muscle Atrophy.

  5.    Both UMN and LMN involvement: Amyotrophic Lateral Sclerosis.

Points about: ALS

  -         Most common type of MND.

  -         Men > Women.

  -         Smoking – Independent risk factor for sporadic ALS.

  -         SPLIT HAND phenomenon: Severe changes in thenar eminence and the relative sparing of hypothenar eminence, observed in EMG study.

  -         Coronal T2WI MRI: Bilateral symmetrical hyper intensity along corticospinal tracts forming a ‘Wine Glass’ appearance.

Impaired neuronal viability is due to:

 -         Superoxide dismutase 1 transgenes.

 -         Hexanucleotide repeats.

 -         ALS gene leading to defective axonal cytoskeleton.

Clinical Features:

  -         Asymmetric muscle weakness.

  -         Normal sensations.

  -         Difficulty in swallowing, chewing and tongue movements. Tongue fasciculation may be present.

  -         Death is due to respiratory failure.

Normal in MNDs:

-         Eye movement.

-         Bladder and bowel.

-         Mentation.

-         Sexual function.

Investigations:

-         EMG: Most confirmatory.

-         Biopsy shows atrophy.

-         Diagnosis is considered definitive if 3 out of 4 areas are involved: bulbar, cervical, and thoracic and lumbosacral motor neurons.

Drugs:

  -         Riluzole:
Reduces glutamate induced exitotoxicity.
Recommended dose is 100mg per day.

  -         Edavarone:

Free radical scavenging agent.
It just slows the disease progression. Recommended dose is 30 – 60 mg per day IV Infusion.

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