Motor Neurone Disease; Benign essential tremor Flashcards
Describe what is meant by motor neuron disease [1]
What is the most common type? [1]
What is the second most commont type? [1]
Motor neurone disease is a term that encompasses a variety of specific diseases affecting the motor nerves. Motor neurone disease is a progressive, eventually fatal condition where the motor neurones stop functioning.
Amyotrophic lateral sclerosis (ALS) is the most common and well-known type of motor neurone disease. Stephen Hawking had amyotrophic lateral sclerosis.
Progressive bulbar palsy is the second most common form of motor neurone disease. It primarily affects the muscles of talking and swallowing (the bulbar muscles).
NB: There is no effect on the sensory neurones. Sensory symptoms suggest an alternate diagnosis.
Describe the pathophysiology of MND [1]
Motor neurone disease involves a progressive degeneration of both the upper and lower motor neurones. The sensory neurones are spared.
The exact cause is unclear, although several mechanisms have been considered. Many genes have been linked with an increased risk of developing the condition. Family history is important as around 5-10% of cases are inherited. There seems to be an increased risk with smoking and exposure to heavy metals and certain pesticides.
Describe the presentation of MND [
The typical patient is a late middle-aged (e.g., 60) man, possibly with an affected relative.
There is an insidious, progressive weakness of the muscles throughout the body, affecting the limbs, trunk, face and speech
- The weakness is often first noticed in the upper limbs
- There may be increased fatigue when exercising
- They can develop slurred speech
Also
* fasciculations
* the absence of sensory signs/symptoms
* the mixture of lower motor neuron and upper motor neuron signs
* wasting of the small hand muscles/tibialis anterior is common
* doesn’t affect external ocular muscles
* no cerebellar signs
* abdominal reflexes are usually preserved and sphincter dysfunction if present is a late feature
Dx of MND? [3]
The diagnosis of motor neuron disease is clinical, but nerve conduction studies will show normal motor conduction and can help exclude a neuropathy.
- Electromyography shows a reduced number of action potentials with increased amplitude.
- MRI is usually performed to exclude the differential diagnosis of cervical cord compression and myelopathy
Describe the treatment for MND [2]
Riluzole
* prevents stimulation of glutamate receptors
* used mainly in amyotrophic lateral sclerosis
* prolongs life by about 3 months
Respiratory care
* non-invasive ventilation (usually BIPAP) is used at night
* studies have shown a survival benefit of around 7 months
Prognosis of MND? [1]
poor: 50% of patients die within 3 years
Describe the presenting features of each type of MNDs:
ALS [2]
Primary lateral sclerosis [1]
Progressive muscular atrophy [3]
Progressive bulbar palsy [2]
ALS
- LMN in arms
- UMN signs in legs
Primary lateral sclerosis:
- UMN signs only
Progressive muscular atrophy
- LMN signs only
- affects distal muscles before proximal
- carries best prognosis
Progressive bulbar palsy
* palsy of the tongue, muscles of chewing/swallowing and facial muscles due to loss of function of brainstem motor nuclei
* carries worst prognosis
Describe what is the thought behind the pathophysiology of essential tremor?
The pathophysiology of essential tremor has not been fully established although the evidence suggests that it is related to pathology in the cerebellum, brainstem, and thalamus which are involved in the motor control circuit.
- It has been identified that essential tremor may be related to increased activity in the cerebellar-thalamic-cortical circuit
- GABA-ergic dysfunction of the cerebellar dentate nucleus and brainstem may lead to dysregulation in this circuit, leading to tremulous activity
Describe the clinical features of essential tremor
Tremor
* Action tremor
* Exacerbated on intentional movements, and usually absent on rest
* Common daily tasks where the tremor is exacerbated includes writing, handling utensils and small objects, drinking, reaching out for objects
* On examination, will worsen on holding the arms outstretched and on finger-to-nose testing
* Typically bilateral
* Asymmetric in nature and generally affects the dominant side more than the non-dominant side
* Primarily affects hands and arms in early stages
* Can sometimes progress over a long time to involve the head, voice, trunk
* Very rarely affects the lower limbs
* Head tremor can be either vertical (nodding head yes) in 25%, or horizontal (shaking head no) in 75%
Tremor frequency
* Moderate to high frequency
* 6-12 Hz
Relieving/exacerbating factors
* Relieving: usually relieved somewhat by alcohol (in approximately 65%)
* Exacerbating: exacerbated by anxiety, excitement, adrenergic stimulation
In some situations, the essential tremor is called ‘essential tremor plus.’
What features would be included in this? [4]
Difficulty with tandem gait
Mild cognitive impairment (typically mild memory impairment)
Slight resting tremor alongside action tremor
NB:
- Often, the presence of these symptoms may confuse the diagnosis and usually will prompt investigation for another differential prior to making the diagnosis of essential tremor plus. This is because the diagnostic criteria below indicates that for the diagnosis of essential tremor, these must be absence of other neurological signs
Differential Diagnosis of Tremor? [6]
Parkinson’s disease
Multiple sclerosis
Huntington’s chorea
Hyperthyroidism
Fever
Dopamine antagonists (e.g., antipsychotics)
How do you differentiate essential tremor with PD? [4]
A lower limb tremor is uncharacteristic and uncommon in essential tremor, therefore presence of such should suggest Parkinson’s disease as the alternative diagnosis
Parkinson’s disease typically presents initially with a unilateral tremor, whereas essential tremor presents bilaterally
Parkinson’s disease is typically a resting tremor, whereas essential tremor is an action tremor
Patients with Parkinson’s disease may have other features of this condition including bradykinesia and rigidity
How do you differentiate BET with dystonic head tremor? [4]
Similarities
* Can both present with head or voice tremor
Differences
* An isolated head and voice tremor excludes essential tremor as a diagnosis
* An isolated head and voice tremor will usually suggest cervical dystonia with dystonic head tremor instead
* The head and neck tremor tends to be more irregular and jerky, while in essential tremor it is more regular and rhythmic
* In essential tremor, the head tremor will mostly subside when resting the head in a supine and supported position, while in cervical dystonia it will often persist despite the resting position
Medical [2] and surgical [2] treatment of essential tremor?
Medical treatment
- first-line medical treatment for essential tremor is either propranolol and primidone
- If required, step-up to using both propranolol and primidone in combination may be trialled
- For patients refractory to these medications, reasonable second-line medications according to UptoDate and BMJ best practice include gabapentin, topiramate and nimodipine
Surgical treatment
- Deep brain stimulation may be indicated for patients w severe disability (directed at nucleus ventralis intermedius of the thalamus)
- Botulinum toxin type A injections
NB: Medical tx witll reduce the tremor amplitude by up to 50%, therefore it is important to educate patients that it is unlikely that their tremor will completely subside
Describe the typical disease course of essential tremor [+]
Typical course of disease
Typically, the patient will experience symptoms for multiple years prior to presenting for medical review, as often the symptoms are mild and not impacting on quality of life or function
As time goes on, the tremor usually gradually worsens
However, it can occasionally worsen in a step-wise manner
For many patients, the tremor remains isolated to the upper limbs
However in some patients there can be spread to other parts of the body, often the head and voice
This typically happens gradually over a long number of years before becoming evident
For a small subset of patients, the tremor may remain stable and not progress over the course of disease
