LMN lesions

• Wasting of affected muscles.
• Fasciculation (spontaneous involuntary twitching) of affected muscles.
• Hypotonia/flaccidity
• Reflexes are reduced or absent.
• Plantars remain flexor.

Chief differential diagnosis = weakness from a primary muscle disease, in which:

• Loss is symmetrical.
• Reflexes are lost later than in neuropathies.
• There is no sensory loss!

Myasthenia gravis causes weakness worsening with use (fatiguability); there is little wasting, normal reflexes, and no sensory loss.

UMN lesions

Damage to motor pathways anywhere from the precentral gyrus of the frontal cortex, to the internal capsule, brainstem, cord, anterior horn cells in the cord.

UMN lesions affect muscle groups, not individual muscles.

Weakness is typically 'pyramidal' in distribution.

• UL extensors are weak.
• LL flexors are weak.
• No muscle wasting.
• Loss of fine finger movements may be greater than expected from the overall grade of weakness.
• Spasticity in stronger muscles. Spasticity = increased tone that is velocity-dependent (in rigidity, increased tone is independent of velocity - it is constant throughout passive movement) and non-uniform (resistance to passive movement that can suddenly be overcome - clasp-knife feel).
• Hyperreflexia (reflexes are brisk).

The reflexes in UMN lesions:
- Babinski sign positive (plantars are upgoing).
- Clonus.
- Hoffman's reflex positive. Neck extension is said to increase sensitivity of this test.

NB: UMN lesions can mimic LMN lesions in the first few hours before the spasticity and hyperreflexia develop.

'Extrapyramidal'

'Extrapyramidal' denotes CNS motor phenomena relating to the basal ganglia.

Basal ganglia's main components = SSSP: Striatum, subthalamic nucleus, substantia nigra, pallidum.

Extrapyramidal lesions cause abnormality with initiation and maintenance of movement. Extrapyramidal symptoms = tremor, rigidity, involuntary movements, dyskinesia (e.g. chorea, athetosis, ballismus, dystonia).

• Dyskinesia = Difficulty or abnormality in performing voluntary muscular movements.
• Chorea = Jerky, involuntary movements, chiefly of the face and extremities.
• Athetosis = Slow, involuntary, wormlike movements of the fingers, toes, hands, and feet.
• Ballismus = Twisting, shaking, and jerking motions.
• Dystonia = Abnormal tone.

Symptoms NOT suggestive of extrapyramidal lesions =

• Bradykinesia/akinesia (slow/absent movement)
• Loss of postural reflexes.
  

Cataplexy

Cataplexy = drop attack triggered by emotion.