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Motor Neurone Disease

From Mediwikis
A 4 minute guide to Motor Neurone Disease, by Soton Brain Hub

Stephen Hawking and the popular 'ice bucket challenge' have thrust this rare disease, annual incidence of 2/100,000, into the spotlight. It is characterised by progressive muscular weakness and eventual death, usually as a result of aspiration or respiratory failure.

Pathophysiology

The upper motor neurone axons (originating in the precentral gyrus) travel in the corticospinal and corticobulbar tracts to the brainstem and anterior horn of the spinal cord. Here they synapse directly with the lower motor neurones which innervate muscle fibres.

Autopsies of those with amyotrophic lateral sclerosis (ALS), the commonest form of MND, have shown atrophy of the precentral gyrus and the anterior horn cells. There have been no valid autopsy reports of other forms of MND.

Epidemiology

Male:female - 2:1.

Average onset 5th-6th decade.

~10% of cases are familial.

Presentation

Onset Symptoms Signs Form of MND
Commonly focal upper (then

lower) limb onset.

Dropping objects.

Weakness, stiffness and

cramping of hand.

Tripping over.

Difficulty climbing stairs.

Heavy legs.

Fatigue when walking.

Mixed UMN and LMN signs. ALS
Bulbar. Slurred speech.

Emotional lability.

Drooling.

Choking.

Mixed UMN (pseudobulbar)

and LMN (bulbar) signs:

  • Wasting and fasciculations of

tongue.

  • Dysarthria.
  • Dysphonia.
  • Dysphagia (late sign).
Progressive pseudobulbar and bulbar

palsy.

Small muscles of hands and

feet first.

Limb weakness. LMN signs only (atrophy,

fasciculations, hyporeflexia).

Progressive muscular atrophy.
Slowly progressive tetraparesis

and pseudobulbar palsy.

Lower limb weakness.

Difficulty swallowing.

Emotional lability.

UMN signs only (leg flexor weakness,

hypertonia, hyper-reflexia, upgoing

plantar responses).

Primary lateral sclerosis.

Diagnosis

There is no gold standard investigation. The Revised El Escorial Criteria is used to diagnose ALS. This criteria states that patients must have evidence of progressive UMN and LMN degenerative signs in the absence of electrophysiological or neuropathological evidence of other disease processes that may explain these signs.

The patient will be referred to neurology and it may take several months for a diagnosis to be made due to the severity of the prognosis. The average patient lives for 3 years.

Investigation

The investigations are focused upon ruling out differential diagnoses. The following investigations may be useful:

  • Electrophysiology
    • Electromyography - fibrillations (spontaneous action potentials produced as muscle fibres lose contact with innervating axon) and fasciculations (spontaneous depolarisation of a LMN causing synchronous muscle contractions)
  • CT/MRI.
  • Blood tests - exclude Vitamin B12/folate deficiency, HIV, Lyme disease and other rare conditions.
  • Muscle biopsy - exclude myopathies.

Management

A multi-disciplinary approach to support the patient and their carers.

Riluzole (neuroprotective agent) is the only disease-modifying drug, increasing life expectancy by 2–4 months.

Symptomatic relief - analgesics, anti-cholinergics (reduce drooling), anti-spasticity agents and anti-depressants.

At later stages, enteral feeding.

NICE recommend the use of non-invasive ventilation as it significantly increases survival.

Refer to palliative care team.

Prognosis

The medial survival is 2–4 years.

The brainstem nuclei (cranial nerves III, IV and VI) and the sacral spinal cord are spared until late in ALS so patients have preserved eye movements, micturition and faecal continence.

90% of patients die in their sleep due to respiratory failure.