Pathology-Motor Neurone Disease (MND)

Pathology-Motor Neurone Disease (MND)
I. Definition & Epidemiology:

Definition: MND is a group of neurodegenerative diseases causing selective loss of motor neurons. This means the nerve cells that control voluntary muscle movement are progressively destroyed.
Epidemiology:
- Rare disease: Annual incidence 1-5 per 100,000.
- Slight male predominance.
- Typical onset: 50-70 years old.

II. Aetiology (Causes):

Mostly Idiopathic: In most cases (90%), the cause is unknown.
Familial (Inherited): Approximately 10% of cases are inherited, showing a genetic component.
Genetic Links: Several genes associated with familial MND have been identified, including SOD1, TDP-43, and FUS.

III. Pathogenesis (Disease Mechanisms):

Poorly Understood: The precise mechanisms driving MND remain largely unclear, even with insights from familial cases.
RNA Metabolism Dysfunction: A leading hypothesis points to defects in RNA metabolism as a crucial factor in motor neuron degeneration. This is based on the properties of TDP-43 and FUS proteins.
TDP-43 & FUS: Both are RNA/DNA-binding proteins with similar structures. Their dysfunction is strongly implicated in MND development.

IV. Clinical Presentation:

Muscular Symptoms: Asymmetrical muscle weakness and wasting (atrophy), muscle twitching (fasciculations), and muscle stiffness (spasticity) in limbs are common early signs.
Bulbar Symptoms: Difficulty with swallowing (dysphagia), chewing, speaking (dysarthria), coughing, and breathing (dyspnea) are characteristic as the disease progresses and affects the muscles controlling these functions.
Cognitive Changes: Cognitive impairment can also occur in some cases.

V. Macroscopic & Microscopic Findings:

Macroscopy (Gross Examination): The anterior roots of the spinal cord (which carry motor neuron axons) are atrophied (shrunken).
Histopathology (Microscopic Examination):
- Selective loss of motor neurons in the motor cortex (brain) and anterior horns of the spinal cord is the defining feature.
- In sporadic (non-inherited) MND, remaining motor neurons often contain abnormal protein inclusions that include ubiquitin and TDP-43.

VI. Prognosis:

Progressive & Fatal: MND is typically progressive, leading to death within a few years.
Cause of Death: Aspiration pneumonia (lung infection from inhaling food or saliva due to swallowing difficulties) is a frequent cause of death.

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