Motor Neuron Disease Flashcards
Definition
Motor neuron disease (MND) is a disorder of both upper and lower motor neurons
- progressive and ultimately fatal
- motor neurons stop functioning (no effect on sensory)
MAIN MOTOR TRACT = Corticospinal; UMN from pre-central gyrus which has:
- Decussation (LATERAL, 90% FIBRES)
- No decussation (ANTERIOR, 10% FIBRES)
Epidemiology, Risk Factors
Middle aged (+40)
Men
Family history: SOD1 (ALS only)
Smoking
Exposure to heavy metals and certain pesticides
Amyotrophic lateral sclerosis (MC)
SOD1 mutation
Affects both UMN + LMN
Can to progress to Bulbar palsy
UMN signs: predominantly affects the corticospinal tracts
LMN signs: also affects anterior horn cells
- Progressive paralysis and eventual respiratory failure
Progressive muscular atrophy
LMN: affecting predominantly the anterior horn cells
Signs: pharyngeal muscle weakness, progressive loss of speech, tongue atrophy
Best prognosis
Primary lateral sclerosis
UMN: Predominantly affects the corticospinal tracts
- arms, legs and face
Movements become slower, pseudobulbar effect,
Progressively bulbar palsy
Affects the suprabulbar nuclei and cranial nerves, producing speech and swallow issues (C9-12)
Progressive degeneration of only LMN
- Muscle wasting
- Clumsy hand movements
- Fasciculations
- Muscle cramps
WORST PROGNOSIS
Signs
Mixed UMN and LMN signs
Spastic paraparesis with brisk reflexes
Fasciculations, especially on the tongue
Dysarthria and dysphagia: particularly in progressive bulbar palsy
Muscle wasting: particularly of small hand muscles and tibialis anterior
Symptoms
Progressive muscle weakness
- weakness first noticed in upper limbs
Falls
Speech and swallow issues: particularly in progressive bulbar palsy
Clumsiness
Fatigue when exercising
Symptoms YOU WONT SEE
No sensory abnormalities (DDx = MS + POLYNEUROPATHIES)
No extraocular involvement (eyes - DDx= MS + MG does)
No cerebellar involvement
Signs YOU WONT SEE
Sphincter dysfunction is rare and would only present as a late feature
Abdominal reflexes are usually preserved
Diagnosis
Clinical diagnosis and excluding other conditions
- Electromyography: Evidence of fibrillation potentials
Nerve conduction studies: Modest reductions in amplitude
MRI spine: imaging can help exclude spinal pathology which may mimic MND, such as cervical cord compression and myelopathy
Pulmonary function tests: patients with MND are at risk of respiratory failure
Treatment
FIRST LINE = RILUZOLE = extend survival by 2-4 months
Respiratory support: patients with reduced FVC can use non-invasive ventilation at home, usually BiPAP; prolongs survival by 7 months
Supportive treatment:
- Antispasmodics: such as baclofen
- Feeding support: many patients require nutritional support, often with PEG tube
- Speech and language therapy
- Physiotherapy
Complications
- Aspiration pneumonia and bronchopneumonia
- Respiratory failure: often occurs in advanced disease when respiratory muscles have been affected
UMN lesions (think hyper)
Lesions from PRE-CENTRAL GYRUS to ANTERIOR SPINAL CORD (everything up)
Hypertonia, rigidity + spasticity (rigid with movement)
Hyperreflexia
No fasciculations
Babinski reflex positive
Power:
- ARMS = FLEXORS > EXTENSORS
- LEGS = EXTENSORS > FLEXORS
LMN lesions (think hypo)
Lesions from ANTERIOR SPINAL CORD to the MUSCLES INNERVATED = everything down
Hypotonia (flaccid) + muscle wasting
Hyporeflexia
Fasciculations
Babinski -ve
Generally decreased power
