Motor neurone disease Flashcards
MND : Anatomy of Corticospinal tract
MOA : Responsible for controlling voluntary movements in the limbs.
Corticospinal tract
1. Origin : Motor cortex
* UMN form part of the corticospinal tract and extend axons into;
2. Mid brain
3. Medulla : UMN crossover
4. Spinal Chord - Anterior horn
UMN synapse with LMN
5. Neuromuscular junction
LMN synapses with muscle
- Movement occurs
MND : Anatomy of Corticobulbar tract
MOA :
* Neural pathway responsible for providing motor innervation to the cranial nerve nuclei in the brainstem,
- which, in turn, control the muscles of the face, head, and neck
Origin : Primary Motor cortex
* Upper motor neurons form part of the corticobulbar tract and extend axons to;
1 . Internal capsule :
* Bundle of nerve fibres - pathway connected cerebral cortex and brainstem
2 .Pons : UMNs cross over
. 3 .Brain stem nuclei : UMN synapse with LMN
* Contains cranial nerve nuclei : facial nerve nucleus, trigeminal nerve nucleus, hypoglossal nucleus } control voluntary movement of head and neck.
Corticobulbar palsy : Clinical features
The degeneration of upper motor neurons in the corticobulbar tract effects the motor commands that influence the function of cranial nerves in the brainstem.
1. Dysarthria and Dysphagia
* Degeneration of the hypoglossal nucleus and nerve leads to tongue weakness and atrophy
2. Dysphagia and Hoarse/Weak voice
* Degeneration of Glossopharyngeal (IX), vagus (X), and accessory (XI) nerves.
3. Facial weakness, loss of expression
* facial nerve nucleus degeneration leads to facial weakness and a loss of voluntary facial movements
Motor neurone disease : Definition
Motor neurone disease involves a progressive degeneration of both the upper and lower motor neurones.
The sensory neuronesare spared.
Motor neurone disease : Incidence
Late - middle aged men (around 60 years old)
Motor neurone disease : Clinical presentation
Onset : Slow, progressive weakness of muscles
1. Limb weakness : worse on exercise
2. Increased, clumsiness and falls
3. Lower motor neuron signs > Upper motor neuron signs
* Both occur
Motor neurone disease : UMN signs/Sx
1 . Hyperreflexia:
* a loss of inhibitory input on the reflex arc.
* This disinhibition results in exaggerated reflex responses, known as hyperreflexia
.
*Clinical Sign: Increased deep tendon reflexes, such as brisk knee jerk reflexes.
2 . Hypertonia/Spasticity
* Disrupts the balance between excitatory and inhibitory signals to lower motor neurons,
* leading to increased muscle tone and spasticity.
Clinical Sign: Resistance to passive movement, with muscles feeling stiff and tense.
3 . Weakness:
* impairs the descending signals that normally facilitate voluntary muscle contraction..
Clinical Sign: Weakness, typically more pronounced in the extensor muscles.
4 . Babinski Sign:**
- normal: the plantar reflex is flexor in response to stimulation.
- Abnormal : extensor (upward) response in the toes and suggests UMN involvement.
Clinical Sign: Babinski sign involves dorsiflexion of the big toe and fanning of the other toes.
Motor neurone disease : LMN signs/Sx
Damage to Lower Motor Neurone causes;
!) Hyporeflexia/Areflexia:
* decreased or absent reflex responses.
* Clinical Sign: Diminished or absent deep tendon reflexes.
2) Hypotonia/Flaccidity:
leads to a lack of muscle tone and atrophy due to denervation.
* Clinical Sign:* Muscles feel floppy, and there is a noticeable loss of bulk.
3) Fasciculations
Spontaneous contractions of a bundle of muscle fibers.
Instability of the motor endplate due to denervation.
- Clinical Sign : Visible twitching or rippling of muscles, often seen under the skin.
4) Muscle Atrophy:
Denervation of muscles leads to disuse atrophy, resulting in a reduction in muscle bulk.
* Clinical Sign:* Noticeable wasting of muscles.
5) Absent Babinski Sign
the Babinski sign is typically absent, as it is a reflection of an upper motor neuron response.
* Clinical Sign: The normal plantar reflex response is observed.
ALS - Definition
- This is a degenerative motor neurone disorder
- Involved both Upper and lower motor neuron lesions
- Lower motor neurone signs
ALS - Aetiology
Genetic mutation : Superoxide Dismutase 1
**MOA **:
* enzyme important for removing free oxygen radicals from neurons
,without this;
* increased free radical injury, which will lead to neuron death.
ALS : Pathophysiology
- Neuronal damage in ;
* Anterior Horn of Spinal Chord : Lower motor neurone affected
* Cortical (Cerebral cortex) : Upper motor neurones affected in the - Coritospinal pathway
- Corticobulbar spinal pathways of cranial nerves
Symptoms dependant on which spinal tract is affected
ALS : Clinical features
- Mixed Upper and Lower motor neuron signs
- Asymmetric limb weakness
- Wasting of small hand muscles
- Faciculations
- Corticobulbar pathway damage :
* Head, Neck weakness
* Dysarthria, Dysphagia
No
* No Sensory symptoms - Bladder and Bowel function spared
* No impact on external ocular muscles
* No Cognitive damage
* No Cerebellar damage
ALS : Diagnosis
- Nerve conduction - r/o neuropathy
- MRI - r/o chord compression
ALS : Management
- Riluzole
Prevents glutamate receptor stimulation
Prolongs life by around 3 months - NIV - for respiratory care
- Nutrition
* percutaneous gastrostomy tube (PEG) is the preferred way to support nutrition and has been associated with prolonged survival
Motor neurone disease : Prognosis
- Eventually, the disease might progress to involve the breathing muscles and can lead to respiratory failure and death.
- poor: 50% of patients die within 3 years
Progressive bulbar palsy : Definition
- Progressive Bulbar Palsy (PBP) is a type of Amyotrophic Lateral Sclerosis (ALS),
- a progressive neurodegenerative disorder that affects the motor neurons in the brain and spinal cord.
- PBP specifically involves the bulbar region, which includes
* the brainstem and the cranial nerves responsible for functions such as speech, swallowing, and facial movements.
Progressive bulbar palsy : Clinical features
Prominently bulbar symptoms - some associated limb weakness from effects on spinothalamic tract
1. Dysarthria : earliest, most prominent symptoms
2. Dysphagia / Tongue atrophy
3. Facial weakness
- Normal Sensation and cognition
Pseudobulbar palsy : Definition
- Neurological condition characterized by the dysfunction of the upper motor neurons that innervate the bulbar muscles.
- “pseudobulbar” - Cranial nuclei and Lower motor neurons are intact
- Primary pathology lies in the upper motor neurons
symptoms mimic those seen in bulbar palsy
Pseudobulbar palsy : Causes
various neurological conditions that affect the upper motor neurons, such as
- Stroke,
- traumatic brain injury
- multiple sclerosis
- neurodegenerative disorders.
Pseudobulbar palsy : Clinical features
-
Bulbar Symptoms:
* dysarthria (difficulty in articulating words), dysphagia (difficulty swallowing), and facial weakness.
2). Upper Motor Neuron Involvement:
* Increased muscle tone and spasticity } common
* overactivity of the upper motor neurons
* stiff and jerky movements.
Subacute combined degeneration of the spinal cord : Definition
- Subacute combined degeneration of the spinal cord
- Due to vitamin B12 deficiency resulting in;
- impairment of the dorsal columns, lateral corticospinal tracts and spinocerebellar tracts
SCD of Spinal Chord : Pathophysiology
Cause
1. Vitamin B12 / Cobalamin deficiency.
- Vitamin B12 required for
synthesis of myelin - DNA repair and maintainance in neuronal cells
- Lack of vitamin B12 leads to;
- Demyelination and degeneration of nerve fibers in the spinal cord.
- Particularly affecting the dorsal (posterior) and lateral columns.
Recreational nitrous oxide inhalation may also result in vitamin B12 deficiency → subacute combined degeneration of the spinal cord.
SCD of Spinal Chord : Risk factors
Risk factors - same as for vitamin B12 deficiency
- Inadequate dietary intake
- Malabsorption disorders
- Medications (e.g., proton pump inhibitors, metformin).
SCD of Spinal Chord : Clinical features
Symmetrical involvement - Symptoms present bilaterally
- Dorsal column affected :
MOA : responsible for transmitting proprioceptive (position sense) and vibratory sensation - resulting in
-
Sensory Ataxia: unsteady, clumsy gait
- Loss of Vibratory Sensation: numbness, tingling, and loss of vibratory sensation, particularly in the lower extremities.
- Paresthesias: “pins and needles” may occur.
-
Lateral Corticospinal Columns:
MOA : responsible for voluntary motor function
Degeneration of this leads to;
- Upper motor neuron signs
- Spasticity and weakness.
- Weakness and Muscle Atrophy
- Difficulty with Fine Motor Skills
- Macrocytic Anemia: pernicious anemia, contributing to fatigue and weakness.
SCD of Spinal Chord : Prognosis
- Prompt managaement - allows for reversal of symptoms
- Untreated - progresses to permanent neurological deficits.
