Motor neuron diseases Flashcards
How are motor neuron diseases characterised
progressive degeneration of motor neurons
Which areas may be affected by MND
- uper motor neurons (pyramidal fibres from cerebral cortex)
- lower motor neurons (motor nerve neuclei of lower brainstem and anterior horn cells of spinal cord)
List the types of MND
- amyotrophic lateal scelorsis (ALS)
- spinal muscular dystrophy
- primary lateral sclerosis
- progressive bulbar palsy
List some of the common features of MND
- onset is usually at middle age
- males are more affected than females
- insidious onset, slow progression
- impairment of motor skill, no sensory loss and sphincter dysfunction
What is the epidemiology of ALS
Male: female (1.5:1)
onset age: 4-60 years old (rare before 20)
List the pathogenesis of ALS
sporadic disorder and the cause is not well defined
- 5-10% inherited
- Cu/Zn superoxide dismutase (SOD1) mutations
- excitotoxic neurtotransmitters
- deficiency of neurotropic factor
- exposure to lead or aluminium
- infection by an unidentified virus
- autoimmunity
Describe the pathology of ALS
- degeneration and death of LMN and UMN
- death of LMN –> atrophy of corresponding muscle fibres (Amyotrophy)
- loss of UMN –> thinning of pyramidal tracts –> lateral column degeneration (lateral sclerosis)
Describe the clinical manifestations of ALS
- insidiously developing asymmetric weakness, usually first evident in one of the limbs
- progressive wasating and atrophy of muscles
- spontaneous twitching or fasciculations
Corticospinal tract involvment: yperactivity of tendon reflexes and spastic resistance to passive movements of affected limbs and pathologic reflexes
Bulbar dysfunction: involves bulbar muscles, difficulty with chewing, swallowing, speech and movements of tongue
involvement of muscles of respiration (late stage): may lead to respiratory paralysis, death
How is ALS diagnosed
- simultaneous upper and lower motor neuron involvement with progressive weakness and the exclusion of other diseases
Definite ALS: upper and lower motor neuron signs in bulbar and 2 spinal regions or upper and lower motor neuron signs in 3 spinal regions
Probable ALS: two regions are involved
Electromyogram: denervation
Muscle or nerve biopsy: help confirm nerve disease
What is the differential diagnosis for ALS
- compression of cervical spinal cord (tumours or intervertebral disc herniation) can produce weakness, wasting and fasiculations in upper limbs and spasticity in legs –> closely resembles ALS
What drug can be used in the treatment of ALS
Riluzole (may diminsh excitotoxicity by diminishing glutamate release)
- can increase survival by about 3 months
- more effective: bulbar disease onset, older age, earlier in disease course
- no effect on strength, respiration or quality of life
- high cost: $1o,000/year
What is the common cause of death in an individual with ALS
respiratory failure
What is spinal muscular atrophy (SMA)
is a hereditary disease of early onset
weakness and wasting of the skeletal muscles are caused by progressive degeneration of the anterior horn cells of spinal cord
What is promary lateral sclerosis and what are the involved regions
- exceedingly rare disorder than arises sporadically in adults in mid to late life
involved regions: corticospinal and corticobulbar tracts
progressive spastic weakness of limbs, preceded or followed by dysarthria and dysphagia
- no fasciculaion, amyotrophy and sensory changes
What is porgressive bulbar palsy
List the clinical features
- found in the LMN of medulla and pons, corticobulbar tracts
Clinical Features: - onset at middle age
- dysphagia and dysarthria, also difficulty with mastcation, cough and even respiration
- on examination: uvula is low, gag reflex is disappeared,and wasting and fasciculation of tongue
- if corticobulbar tracts are affected: jaw reflex is exaggerated, chracterised by spontaneous or unmotivated crying and laughing from time to time in later stage
- progression is rapid and prognosis is poor. respiratory muscle paralysis and pneumonia may lead to termination of life in 1-3 years
