Motor Neurone Disease

Epidemiology
The incidence is approximately 2 in 100 000 population per year and the average age of onset is roughly 65 years.

Types:
Amyotrophic lateral sclerosis ( ALS )

• Fundamental to the diagnosis is progressive weakness with mixed upper and lower motor neuron signs. Brisk reflexes in the presence of local wasting is a strong clue to the diagnosis.
• Visible fasciculations are usually prominent but tend to fade as the illness progresses.
• Differential diagnosis includes cervical spondylotic myeloradiculopathy and paraneoplastic neuromuscular syndrome.

Progressive muscular atrophy:

• True lower motor neuron MND is rare because many patients develop upper motor neuron signs at some point in the disease and are probably best classified as lower motor neuron predominant ALS.
• Differential diagnosis includes conduction block neuropathy, paraneoplastic neuropathy, X linked spinobulbar muscular atrophy ( Kennedy's syndrome ) and adult onset spinal muscular atrophy.

Primary lateral sclerosis:

• rare and accounts for 1 - 2% of MND.
• It is characterised by an ascending spastic tetraparesis with involvement of speech in the majority by 3 years.
• Urinary urgency is common.

Flail arm variant:

• Bilateral weakness and wasting of the proximal upper limb which may not spread to other regions for a number of years is sometimes associated with a dropped head.
• Despite proximity of the affected segments to the respiratory neurons, vital capacity may be unaffected until late in the disease.

Lower limb onset:

• It may remain confine to lower limb and present with with gradual ascending distal weakness.

Progressive bulbar palsy:

• The speech and swallowing involvement is the early features of a condition which rapidly generalises to the limbs and respiratory msucles and has a poor prognosis.

Investigations:
Essential

• Blood test - FBC, eLFT, Ca/PO4, ESR, CK and plasma protein electrophoresis.
• Nerve conduction study and EMG
• MRI spine / brain as indicated by clinical signs

In selective cases

• Blood test - B12, antineuronal antibodies, HIV serology, lyme serology and antiacetylcholine receptor antibodies
• Lumbar puncture
• Muscle biopsy

Treatment:
Aim for supportive treatement.
Riluzole is currently the only drug licensed for the treatment of MND.

• The probability of survival at 1 year after starting the drug is 9 % greater than the placebo ( 2 -3 months greater life expetancy ).
• There is no evidence of any effect on quality of life or improvement in specific symptoms.