Upper gives spasticity and brisk reflexes; lower gives wasting and absent reflexes
Mnemonic
“Everything goes up in upper, everything goes down in lower”:
| Upper motor neurone | Lower motor neurone | |
|---|---|---|
| Tone | Increased, spastic | Reduced, flaccid |
| Reflexes | Brisk, clonus | Absent or reduced |
| Plantars | Extensor (Babinski) | Flexor |
| Wasting | Late, disuse only | Early and marked |
| Fasciculation | Absent | Present |
| Pattern of weakness | Pyramidal: extensors weak in the arm, flexors weak in the leg | Follows the nerve or root |
“Fasciculation is the giveaway for lower motor neurone.”
The pyramidal pattern is worth knowing precisely: in the arm the extensors are weaker, in the leg the flexors are weaker, which is what produces the flexed arm and extended leg of a hemiplegic posture.
Motor neurone disease is the classic combination of both, giving wasting and fasciculation alongside brisk reflexes and extensor plantars, with no sensory signs.
Expansion
| Feature | Upper motor neurone | Lower motor neurone |
|---|---|---|
| Tone | Increased (spastic) | Decreased (flaccid) |
| Reflexes | Brisk, with clonus | Absent or reduced |
| Plantar response | Extensor (Babinski) | Flexor |
| Wasting | Minimal (disuse only) | Marked |
| Fasciculation | Absent | Present |
| Pattern of weakness | Pyramidal: extensors weak in the arm, flexors weak in the leg | Follows the nerve or root |
Spasticity is velocity dependent and shows the clasp-knife phenomenon, in contrast to the lead-pipe or cogwheel rigidity of extrapyramidal disease.
An important caveat: in an acute upper motor neurone lesion such as stroke or spinal cord injury, there is an initial period of flaccidity and areflexia (spinal shock) lasting days to weeks before spasticity develops.
Motor neurone disease is the classic condition combining both, with wasting and fasciculation alongside brisk reflexes.