Pattern recognition in neurology Flashcards
Define an upper motor neuron (UMN) lesion
These are caused by damage to motor pathways (corticospinal tracts) anywhere from motor nerve cells in the precentral gyrus of the frontal cortex down to the synapse with the anterior horn cells in the spinal cord
Define a lower motor neuron (LMN) lesion
These are caused by damage anywhere from anterior horn cells in the spinal cord, nerve roots, plexi or peripheral nerves
What are the typical features of UMN lesions in terms of:
- Weakness distribution
- Sensory loss
- Reflexes
- Sphincter function
- Muscle tone
- Muscle bulk
- Weakness - pyramidal/ corticospinal pattern of weakness = weakness is in the extensors of the arms and in the flexors of the legs
- Weakness distribution differs depending if its hemispheric, parasagittal frontal lobe lesion or a spinal cord lesion
- Sensory loss - central pattern
- Reflexes - hyperreflexia, also +ve babinskis sign (due to loss of inhibitory modulation from descending pathways)
- Sphincter function - sometimes impaired
- Muscle tone - increased
- Muscle bulk - sometimes increased (hypertrophy) or little/none
What are the 3 main distribution patterns of corticospinal/pyramidal weakness associated with UMN lesions?
- Hemispheric: contralateral pyramidal weakness in face, arm, leg (homunculus!)
- Parasagittal frontal lobe lesion: Paraparesis (of legs)
- Spinal cord: pyramidal weakness below the level of the lesion; cervical: arms and legs, Thoracolumbar: legs
Go over signs caused by muscle disease, NMJ disease or functional weakness
What are some of the causes of UMN lesions
- Occurs with acute stroke syndromes, space occupying lesions, and spinal cord problems
- Can usually be determined by body segments involved and accompanying signs
What typical UMN pattern would each of the following lesions result in:
- Hemispheric lesion
- Parasagittal frontal lobe lesion
- Spinal cord lesion
- Hemispheric lesion (so the lesion is just affecting one hemisphere ==> only the R or L hemispheres precental gyrus is affected) presents with pyramidal weakness in the face, arm and leg (hemiparesis = partial paralysis of one side of the body)
- Parasagittal (= adjacent or parallel to sagittal plane) frontal lobe lesion - this lesion is affecting essentially the motor homonculus of the leg region in both sides of the precentral gyrus ==> this will result in a paraparesis = partial paralysis of lower limbs
- Spinal cord lesions result in pyramidal weakness below the level of the lesion e.g. in a cervical lesion the arms & legs would be affected in a pyramidal fashion, and in a throacolumbar lesion just the legs would be affected in a pyramidal fashion
What are the features suggestive of a lower motor neuron lesion, in terms of:
- Weakness distribution
- Sensory loss
- Reflexes
- Sphincter function
- Muscle tone
- Muscle bulk
- Weakness distribution - weakness in the muscles supplied by the involved spinal cord segment (anterior horn specifically otherwise it would be UMN), nerve root, part of plexus or peripheral nerve
- Sensory loss - None, glove, stocking, peripheral nerve or root distribution
- Reflexes - normal or decreased, babinskis sign normal
- Sphincter function - usually normal except for in e.g. cauda equina
- Muscle tone - Decreased
- Muscle bulk - wasting
What are some of the causes of LMN lesions ?
motor neuron disease, spinal muscular atrophy, (lead poisoning, poliomyelitis,…)
If there is peripheral nerve involvement in a LMN lesion how does it typically present?
- Symmetrical (often length dependent) polyneuropathy (golve and stocking) with weakness and sensory symptoms: frequent complication of diabetes. Other aetiologies include a variety of toxic (alcohol) or metabolic insults as well as heritable disorders (often young onset and skeletal deformities)
- Mononeuropathy as a result of nerve compression (carpal or tarsal tunnel syndrome, ulnar neuropathy, radial neuropathy) or mononeuritis multiplex (asymmetric polyneuropathy), which occurs in the context of diabetes or vasculitis
What are the major mononeuropathies and their signs?
What is the typical features of neuromuscular junction pathology and give the main conditions that causes this
- fatiguable weakness
- normal or decreased tone
- normal tendon reflexes
- No sensory symptoms!
Myasthenia gravis, Lambert-eaton syndrome and botulism
What is the typical features of muscle disease
- weakness is usually symmetrical and proximal,
- wasting (usually proximal)
- decreased tone
- decreased or absent tendon reflexes
What type of pathology do each of the following patterns of sensory loss suggest:
- Glove and stocking pattern
- Sensory level
- Haemianaesthesia
- Dissociated sensory loss
- Stocking (and later glove) pattern - implies length dependent neuropathy often diabetes or alcohol
- Sensory level - implies a spinal cord lesion
- Haemianaesthesia - suggests contralateral cerebral lesion, or with no other signs a non-organic disorder
- Dissociated sensory loss - loss with lost spinothalamic (temperature / pain) but preserved dorsal column (vibration, light touch, proprioception) suggests hemicord damage (anterior spinal artery syndrome, Brown-Sequard syndrome, syringomyelia
What are the signs of cerebellar pathology
- Cerebellar gait is broad-based and unsteady
- Intention tremor / ataxia is assessed in the arms by finger-nose test and in the legs by knee-heel testing
- Tremor gets exaggerated the nearer the target
- Dysdiadochokinesis: clumsy fast alternating movements
- Nystagmus and dysarthria are additional features of cerebellar disorders
