Weakness Flashcards
what is the upper motor neuron pathway
cortex > subcortical tracts > internal capsule > brainstem (decussation in pyramids) > spinal cord > anterior horns
what is the lower motor neuron pathway
follows directly on from upper mn
ventral roots > plexi > peripheral nerves > neuromuscular junction > muscle
what is pyramidal weakness
in upper motor neuron lesions unless paralysis is complete (plegia) a specific pattern is seen
in upper limbs, extensors are weaker than flexors
in lower limbs, flexors are weaker than extensors
what does the suffix paresis mean
mild-moderate weakness
what does the suffix plegia mean
more severe weakness
how are weakness patterns catergorised
according to the limb affected
mono - single limb (arm or leg)n
para - both legs
tetra - all four limbs (quadra is also used)
hemi - affecting arm and leg on one side
what is the cortex
descending motor pathways begins here in the primary motor cortex
organised by body regions
large areas devoted to tongue, face and hand
lower limb is given a relatively smaller region on medial surface
lesions will selectively affect certain regions
difference between cortical and diffuse lesiosns
cortical lesions only affect a selected region
diffuse lesions (major infarction) will affect a large area
how do lesions in other upper motor neurons affect the body
lesions outwith the cortex affect broader territory
this is due to tracts travelling closely together
what other clues are there to cortical lesions
seizures
other cortical deficits such as aphasia
how do lesions in the corona radiata and capsule affect the body
lesions here affect broad anatomical territory (eg hemiparesis)
what is the key to localisation of brainstem lesions
corticospinal tract decussates at the pyramids in the medulla
cranial nerves emerging from the brainstem tend to travel on the same side they emerge from
this leads to crossed signs - ipsilateral cranial nerve lesion contralateral signs in limbs
often lesions are very focal
describe a cervical cord lesions
lesions affecting bilateral cord will produce tetraparesis/plegia
spasticity and brisk reflexes will be present, with upgoing plantars (Babinski reflex)
other markers may be sensory loss and a disturbance to bowel and bladder
describe thoracic cord lesions
will only produce weakness in lower limbs
spastic tone, pyramidal weakness, brisk reflexes upgoing plantars
sensory disturbance
sphincter disturbance
what is different about the cauda equina compared to the rest of the spinal cord
nerve roots descend before exiting via the foramina
these roots also carry autonomic and sensory fibres
what can lesions in the cauda equina cause
bilateral paralysis
sensory loss
LMN signs (eg areflexia)
loss of bladder/bowel function
cauda equina syndrome is an emergency, threat of permanent paralysis
what is radiculopathy
compression of nerves where they exit the spinal canal
what are the causes of radiculopathy
prolapsed intervertebral disc
facet joint hypertrophy
spondylolisthesis
radiculitis (inflammation)
symptoms of radiculopathy
pain which radiates down the nerve (radicular pain) dermatomal sensory loss with or without weakness in the site (LMN signs on exam)
examination may elicit characteristic pain via provocative manoeuvres, loss of reflexes in affected territory
what are plexi and how does a lesion impact them
plexi are where spinal nerves combine and individual nerves emerge
lesions here produce a pattern of weakness not conforming to an individual root territory, nor peripheral nerve
impact of peripheral nerve lesions
lesions here affect individual nerves (mononeuropathy)
signs will reflect loss of function in the region supplied by the specific nerve
usually sensory, can be with or without motor features
some nerves are sensory or motor only
how do peripheral nerve lesions occur
nerves are damaged
can be due to a variety of processes such as compression, tumours or inflammation
describe polyneuropathy
multiple nerves affected in multiple limbs (+/- cranial nerves)
various patterns exist but in general longest nerves are damaged first (‘glove and stocking’ sensory loss, distal weakness)
reflexes are diminished or absent
chronically will see wasting, sometimes fasciculations
what is the neuromuscular junction
synapse between motor neuron and muscle
what does issues with the NMJ appear as
fatigable weakness (sustained exertion on bedside testing causes decreasing power)
usual pattern is weakness affecting proximal muscles, ocular muscles, bulbar muscles, neck muscles
sensation is normal and reflexes are unaffected
what is myasthenia gravis
autoimmune disorder where there are antibodies to acetylcholine receptor on muscle
what is the treatment for myasthenia gravis
pyridostigmine (acetylcholinesterase)
immunosuoression
supportive measures
in some cases surgery
avoid drugs which may worsen the disorder
what is muscle myopathy
when many different diseases exist affecting muscles
many different patterns exist
general pattern of proximal weakness, fatigability is not seen, reflexes are generally preserved, sensation is normal
other features include characteristic regions of atrophy (or hypertrophy), contractures, pain, dysmorphic features
what is polymyositis
autoimmune disorder causing muscle inflammation
may be associated with underlying cancer
what is the treatment for polymyositis
immunosuppression
supportive measures
screen for underlying cancer and treat if present
