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Motor neurone disease

Introduction

Motor Neurone Disease (MND) is a progressive neurodegenerative disorder that affects motor neurones in the brain and spinal cord, leading to muscle weakness and wasting. The most common form of MND is Amyotrophic Lateral Sclerosis (ALS).

Epidemiology

  • Incidence: Approximately 2-3 per 100,000 people per year.
  • Prevalence: Around 5-7 per 100,000 people.
  • Age of onset: Typically between 50-70 years old.
  • Gender: Slight male predominance.

Pathophysiology

MND primarily affects the upper motor neurones in the brain and lower motor neurones in the spinal cord. The exact cause is unknown, but several mechanisms are proposed:

  • Genetic Factors: Mutations in genes like SOD1, C9orf72, TARDBP, and FUS.
  • Protein Aggregation: Abnormal protein accumulation in motor neurones.
  • Oxidative Stress: Imbalance between the production of free radicals and the body’s ability to counteract their harmful effects.
  • Excitotoxicity: Excessive activation of glutamate receptors leading to neuronal damage.

Clinical Features

MND presents with a combination of upper and lower motor neurone signs:

  • Upper Motor Neurone Signs: Spasticity, hyperreflexia, Babinski sign.
  • Lower Motor Neurone Signs: Muscle weakness, atrophy, fasciculations.
  • Bulbar Symptoms: Dysarthria, dysphagia, tongue atrophy.
  • Respiratory Symptoms: Dyspnoea, respiratory muscle weakness.

Diagnosis

Diagnosis of MND is primarily clinical, supported by investigations to exclude other conditions:

  • Clinical Examination: Identification of upper and lower motor neurone signs.
  • Electromyography (EMG): Shows denervation and reinnervation in affected muscles.
  • Nerve Conduction Studies (NCS): Usually normal, helps exclude peripheral neuropathies.
  • Neuroimaging: MRI to rule out other structural brain and spinal cord lesions.
  • Genetic Testing: For familial cases.

Management

There is no cure for MND, but management focuses on symptom control and supportive care:

  • Medications: Riluzole to slow disease progression; Edaravone for neuroprotection.
  • Symptom Management: Antispasmodics for spasticity, non-invasive ventilation for respiratory support.
  • Multidisciplinary Care: Physiotherapy, occupational therapy, speech and language therapy.
  • Palliative Care: Focus on quality of life, pain management, and psychological support.

Prognosis

The prognosis of MND is generally poor, with most patients surviving 2-5 years after diagnosis. However, there is significant variability, with some patients living longer. Factors influencing prognosis include age of onset, disease progression rate, and respiratory function at diagnosis.

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