Clinical Differentiation of Weakness Arising from Different Areas of the Nervous System
| Location of Lesion | Pattern of Weakness | Associated Signs |
|---|---|---|
| Upper motor neuron | ||
| Cerebral cortex | Hemiparesis (face and arm predominantly, or leg predominantly) | Hemisensory loss, seizures, homonymous hemianopia or quadrantanopia, aphasia, apraxias, gaze preference |
| Internal capsule | Hemiparesis (face, arm, leg may be equally affected) | Hemisensory deficit; homonymous hemianopia or quadrantanopia |
| Brainstem | Hemiparesis (arm and leg; face may not be involved at all) | Vertigo, nausea and vomiting, ataxia and dysarthria, eye movement abnormalities, cranial nerve dysfunction, altered level of consciousness, Horner's syndrome |
| Spinal cord | Quadriparesis if midcervical or above | Sensory level; bowel and bladder dysfunction |
| Paraparesis if low cervical or thoracic | ||
| Hemiparesis below level of lesion (Brown-Séquard) | Contralateral pain/temperature loss below level of lesion | |
| Motor unit | ||
| Spinal motor neuron | Diffuse weakness, may involve control of speech and swallowing | Muscle fasciculations and atrophy; no sensory loss |
| Spinal root | Radicular pattern of weakness | Dermatomal sensory loss; radicular pain common with compressive lesions |
| Peripheral nerve | ||
| Polyneuropathy | Distal weakness, usually feet more than hands; usually symmetric | Distal sensory loss, usually feet more than hands |
| Mononeuropathy | Weakness in distribution of single nerve | Sensory loss in distribution of single nerve |
| Neuromuscular junction | Fatigable weakness, usually with ocular involvement producing diplopia and ptosis | No sensory loss; no reflex changes |
| Muscle | Proximal weakness | No sensory loss; diminished reflexes only when severe; may have muscle tenderness |