Paresis and paralysis - classification, etiology, pathogenesis, and clinical manifestations.
Paresis: Partial loss of voluntary motor function; means weakness.
Paralysis: Complete loss of voluntary motor function.
Classification
- 1 According to distribution
- 2 According to cause (neuroanatomical level)
Etiology (Causes)
Upper motor neuron (UMN) causes
- Stroke (cerebral infarct or hemorrhage ).
- Traumatic brain injury.
- Multiple sclerosis.
- Spinal cord injury (above anterior horn).
Lower motor neuron (LMN) causes
- Poliomyelitis (anterior horn cell damage).
- Peripheral nerve injury (trauma, compression).
- Guillain- Barré syndrome (acute inflammatory demyelination).
- Amyotrophic lateral sclerosis (affects both UMN and LMN).
Other causes
- Neuromuscular junction disorders (e.g., myasthenia gravis).
- Myopathies (muscle diseases, e.g., muscular dystrophy).
Pathogenesis
UMN lesion pathogenesis
- Damage to corticospinal (pyramidal) pathways above anterior horn cell.
- Loss of inhibitory control → overactivity of spinal reflexes.
- Imbalance between excitatory and inhibitory signals.
LMN lesion pathogenesis
- Damage to anterior horn cell or peripheral motor neuron.
- Loss of direct innervation to muscles.
- Leads to denervation and muscle fiber atrophy.
Clinical manifestations
UMN lesion features
- Weakness: more pronounced in extensors of upper limbs and flexors of lower limbs (classic pyramidal pattern).
- Hyperreflexia (exaggerated tendon reflexes).
- Spasticity (increased muscle tone, velocity- dependent).
- Clonus (rhythmic contractions after sudden stretch).
- Babinski sign positive (toe extension when sole is stroked).
- No significant muscle atrophy early.
LMN lesion features
- Weakness: variable distribution depending on nerve.
- Hyporeflexia or areflexia (decreased or absent reflexes).
- Flaccidity (decreased tone).
- Fasciculations (visible spontaneous muscle twitches).
- Muscle atrophy (due to denervation).
Additional clinical patterns
- Monoplegia/ monoparesis: often from cortical or peripheral nerve lesion (e.g., radial nerve palsy).
- Hemiplegia/hemiparesis: usually from stroke or brain lesion affecting one hemisphere.
- Paraplegia/paraparesis: often spinal cord injury below cervical level or bilateral cortical leg area lesion.
- Tetraplegia/quadriparesis: high cervical cord injury or diffuse brainstem damage.