Motor Neurone Disease

Question 1

Motor neurone disease presentation

Answer 1

This man complains of gradually increasing weakness. Please examine him neurologically.

Question 2

Clinical signs of Motor neurone disease

Answer 2

1. Inspection: wasting and fasciculation
2. Tone: usually spastic but can be flaccid
3. Power: weak
4. Reflexes: absent and/or brisk. (Absent knee jerk with extensor plantar reflexes.)
5. Sensory examination is normal
6. Speech: dysarthria may be bulbar (nasal, ‘Donald Duck’ speech, due to palatal weakness) or pseudo bulbar (‘hot potato’ speech, due to a spastic tongue).
7. Tongue: wasting and fasciculation (bulbar) or a stiff spastic tongue with brisk jaw jerk (pseudo‐bulbar).
8. There is NO sensory, extra‐ocular muscle, cerebellar or extra‐pyramidal involvement.
9. Sphincter and cognitive disturbance occasionally seen.

Question 3

Discussion of MND

Answer 3

1. MND is a progressive disease of unknown aetiology
2. There is axonal degeneration of upper and lower motor neurones

Question 4

Classification of motor neurone disease

Answer 4

MND may be classified into three types, although there is often some overlap:
1. Amyotrophic lateral sclerosis AML (50%): affecting the cortico‐spinal tracts predominantly producing spastic paraparesis or tetraparesis.
2. Progressive muscular atrophy PMA (25%): affecting anterior horn cells predominantly producing wasting, fasciculation and weakness. Best prognosis.
3. Progressive bulbar palsy PBP (25%): affecting lower cranial nerves and suprabulbar nuclei producing speech and swallow problems. Worst prognosis.

Question 5

Investigation in MND

Answer 5

1. Clinical diagnosis
2. EMG: fasciculation
3. MRI (brain and spine): excludes the main differential diagnoses of cervical cord compression and myelopathy and brain stem lesions

Question 6

Treatment of MND

Answer 6

1. Supportive, e.g. PEG feeding and NIPPV
2. Multidisciplinary approach to care
3. Riluzole (glutamate antagonist): slows disease progression by an average of 3 months but does not improve function or quality of life and is costly

Question 7

Prognosis of MND

Answer 7

1. Most die within 3 years of diagnosis from bronchopneumonia and respiratory failure. Some disease variants may survive longer.
2. Worst if elderly at onset, female and with bulbar involvement.

Question 8

Causes of generalized wasting of hand muscles

Answer 8

A. Anterior horn cell
1. MND
2. Syringomyelia
3. Cervical cord compression
4. Polio
B.Brachial plexus
1. Cervical rib
2. Pancoast’s tumour
3. Trauma
C. Peripheral nerve
1. Combined median and ulnar nerve lesions
2. Peripheral neuropathy
D. Muscle
1. Disuse atrophy, e.g. rheumatoid arthritis

Question 9

Fasciculation

Answer 9

• Def: Visible muscle twitching at rest
• Cause: axonal loss results in the surviving axons recruiting and innervating more myofibrils than usual resulting in large motor units
• Seen commonly in MND and syringomyelia