Motor neurone signs

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Disease of the motor system can roughly be divided into upper motor neurone problems - due to disease between the neurones in the cerebral cortex and the anterior horn, lower motor neurone problems - due to disease of nerves from the anterior horn to the muscle, cerebellar disease, and disease of the basal ganglia. This may present with different symptoms summarised below.


Motor pathways (note: different motor fibres decussate at different levels - this is a hugely simplified picture) 


Upper vs lower motor signs
Upper motor neuron lesions include diseases such as cerebral vascular events, space occupying lesions in the brain or trauma and haemorrhage in the brain. Disease of the upper motor neurone causes weakness as signals cannot travel down to the muscles, however it also reduces the inhibitory signals modulating muscle movements, leading to exaggeration of reflexes, spasticity and stiffness.

Lower motor neuron disease include guilliane barre syndrome, and trauma or injury to peripheral nerves. In lower motor lesions, no signals are able to reach the muscle. This causes reduced tone, reduced or absent reflexes and wasting. Fasiculations occur due to uncoordinated self excitation of muscles.

Upper motor neuron
Lower motor neuron
Increased tone, spasticity.
Reduced tone, fasciculations
Hyperreflexia, upgoing plantars
Hyporeflexia, downgoing plantars.
Weakness in the pyramidal pattern - relative weakness of the extensors of the arm and flexors of the legs, weakness of the brachioradialis leading to a pronator drift (turning of the affected arm when the patient is told to hold arms out with palms up and eyes closed)
Muscle wasting throughout (in the long term)



Cerebellar disease

The cerebellum modulates motor signals from the motor cortex to help coordination of movements. Disease of the cerebellum can cause the following problems (with the mneumonic DANISH).

Dysdiadocokinesia - difficulty with rapid alternating movements, tested by asking patient to turn their hands back and forth on their palm. 
Ataxia - disordered muscle movement - usually shown on gait. 
Nystagmus- involuntary eye movement (H test) 
Intentional tremor - Tremor as patient reaches for a far object, shown by finger nose test and heel shin test. 
Slurred speech 
Hypotonia - Hypotonia is a minor sign

Basal ganglia disease
The basal ganglia acts as a filter to inhibit and allow movements. Disorders of the basal ganglia results in hypokinetic or hyperkinetic conditions. Examples of this include parkinson's disease where patients have difficulty initiating movements, or huntingdon's disease where patients have involuntary jerky movements (chorea).

Douglas G, Nicol F, Robertson C, Macleod's clinical examination, 12th ed. Edinburgh, Churchill livingstone, 2009. 
Prof A Zeaman, Teaching session on neurology, [small group teaching session] 12/05/2014. 
https://www.ole.bris.ac.uk/bbcswebdav/institution/Faculty%20of%20Medicine%20and%20Dentistry/MB%20ChB/Hippocrates%20Year%203%20Medicine%20and%20Surgery/Neurology%20-%20Presenting%20complaints/page_29.htm
http://en.wikipedia.org/wiki/Basal_ganglia_disease

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