It is possible to differentiate between UMN dysfunction and LMN dysfunction by careful assessment of the clinical signs.
UMN lesions usually present with while LMN lesions present with
paralysis, hypertonicity and hyperreflexia,
paralysis, hypotonicity and hyporeflexia.
Once it is decided that the lesion is in the central nervous system it must be determined which part of the central nervous system is affected.
UMN Lesions
1.
lesions occur in the UMN’s of the corticospinal tract on the contralateral side to the symptoms. Pyramidal lesions present as impaired skilled movement of the distal limb, impaired hip flexion, impaired shoulder abduction, muscular weakness, hyperreflexia of the distal limb and spastic paralysis of the distal limb, hip flexors and shoulder abductors. There is little or no atrophy seen with pyramidal lesions. lesions occur in the UMN’s of the reticulospinal tract on the contralateral side to the symptoms. Extrapyramidal lesions present as impaired extensor reflex, impaired movement of the head in response to visual stimulus, ataxia or loss of balance when head is moved, spastic paralysis, dyskinesia / akinesia, akathisia and involuntary contraction of postural skeletal muscle.
2.
When both the pyramidal and the extrapyramidal regions are affected by a large lesion or by multiple lesions the clinical signs are ataxia that is increased with circling and unilateral spastic paralysis, hemiplasia, or monoplasia that is especially marked in the distal limb. Central nervous system lesions may not affect the UMN’s directly. Lesions in the brain can impact the motor function of muscles as higher areas of the brain have influence over the movement of the body. The cerebrum, cerebellum, brainstem and the vestibular system all impact the function of the motor neurons. 3. Cerebral lesions are clinically seen as dementia, hysterical flight, aggression, stupor, loss of training, loss of recognition of owner or handler, movement such as pacing or weaving, compulsive circling toward the affected side, seizure, blindness though the pupils respond to light, head pressing, coma and death.
4.
lesions are seen as dysmetria of the limbs on the ipsilateral side, contralateral head-tilt, intention tremor especially noticeable in the head and incoordination.
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