Motor neurone disease most commonly presents with upper or lower motor neurone signs, or a mixture of the two. The disease affects limb muscles or those supplied by cranial nerves.

The disease is of unknown aetiology and results in pathological changes in the anterior horn cells, the motor nuclei of the medulla, and the corticospinal tracts.

Characteristics of lower motor neurone disease include: weakness and wasting, hypotonicity, decreased reflexes, fasciculation.

Characteristics of upper motor neurone disease include: weakness, spasticity, increased tendon reflexes with clonus, extensor plantar response.

It is important to note that in this condition both upper and lower motor neurone signs can be found in the same limb.