UMN vs LMN Flashcards
what are examples of UMN diseases?
PLS, traumatic brain injury, spinal cord injury, MS, stroke, huntingitons
what are examples of LMN diseases?
Poliomyelitis, spinal muscular atrophy, bells palsy
give a disease that involves both UMNs and LMN
ALS
what are the key presentations of UMN diseases?
Weakness – the extensors are weaker than the flexors in the arms, but the reverse is true in the legs
Muscle wasting is absent or slight
Hyperreflexia with clonus
Spasticity
No fasciculations
Babinski sign positive – extended hallux and flaring of remaining digits
Hoffmann’s sign is positive if flexion and sudden release of the terminal phalanx of the middle finger result in reflex flexion of all the digits. This is a sign of the presence of reflex activity. It is positive in, but not specific to, upper motor neuron lesions.
Pronator drift – Patient is asked to hold fully extended arms straight out in front with palms facing upward. If a lesion is present when the patient is asked to close his/her eyes the arm on the affected side pronates due to the difference in muscular tone between pronators and supinators.
what are the key presentations of LMN diseases?
Weakness – limited to focal or root innervated pattern
Muscle Wasting – prominent in a focal pattern
Reflexes – absent or reduced in a lower motor neuron lesion
Fasciculations present in the associated muscle group
Babinski sign absent – downward going digits
how would you differentiate between an UMN lesion and a LMN lesions?
E.g. stroke (UMN) = weakness in face sparing the forehead and the patient is able to close eyes vs. Bell’s palsy (LMN) = weakness in face including the forehead and eyelid difficult to shut
what is the first line investigation for an upper motor neurone problem?
UMN - neuroimaging (from lesion upwards)
what are the first line investigations for LMN problems?
LMN - EMG, nerve conduction studies
