Amyotrophic Lateral Sclerosis (MND)

Amyotrophic Lateral Sclerosis/ Motor Neurone Disease/ Lou Gehrig’s disease

ALS is a neurodegenerative disorder with relentless decline. It affects both the upper and lower motor neurons, and is characterized by the progressive degeneration/ death of the motor neurons of the brain, motor cortex and spinal cord. Symptom onset and progression varies between individuals, but typically involves spasticity, facsiclulations and progressive weakness and atrophy that eventually results in failure of the respiratory muscles. Death, typically from respiratory failure, usually occurs within 2 to 4 years (80% dead by 5 years). There are rare cases (Stephen Hawking), whereby ALS suffers have exceeded life expectancy.

Pathophysiology

Motor neurons in the brain, motor cortex and spinal cord begin to degenerate and die. This in turn results in weakness developing in the muscles which the nerve innervates, subsequently resulting in atrophy of the muscle. The exact pathophysiology of ALS is unknown,  however various suggestions such as glutamate (a neurotransmitter) toxicity and free radical toxicity have been put forward. The use of a glutamate release inhibitor as one of the only accepted forms of treatment to ALS gives credence to this theory, however the true pathophysiology is still undetermined.

Symptoms and Clinical Features

Early onset symptoms vary in terms of site depending on which initial motor neurons are involved. In Limb Onset ALS, often the legs experience weakness distally first but site is highly variable. Patients typically report difficulty walking, tripping over and a foot drop which drags along the ground. Upper limbs may be affected, with the patient complaining of difficulty performing tasks such as doing up buttons on a shirt or writing.

Bulbar Onset ALS involves the motor neurons of the medulla oblongata (brain stem) being affected first, with initial symptoms including difficulty speaking (dysarthria), swallowing (dysphagia) and loss of tongue mobility. Less commonly Respiratory Onset ALS whereby the respiratory/ intercostal muscles and thus breathing are affected.

On examination

Typically on performing a neurological examination, upper motor neuron signs are present (brisk reflexes and upward plantar response/ babinski sign), however as ALS has combined UMN + LMN involvement, lower motor neuron signs may be present in certain cases.

The neurological exam will likely demonstrate widespread muscle weakness and atrophy of the affected muscles. Sensory reflexes are normal.

Diagnosis

Diagnosis of ALS typically involves assessment of clinical presentation and neurological examination findings. Additional investigations can support the diagnosis of ALS and rule out other pathologies with similar presentation to ALS.

Electromyelography (EMG) can be used to determine the electrical activity within the muscle.

“El Escorial criteria for diagnosing ALS:

  • Clinically Definite ALS: Upper and lower motor neuron signs in three or more regions. Regions are defined as bulbar, cervical, thoracic, or lumbar.
  • Clinically Probable ALS: Upper and lower motor neuron findings in two regions or having upper motor neuron findings anatomically rostral (above) lower motor neuron findings. (therefore increased reflexes in the arms with wasting and fasciculations in the legs would qualify, but not the other way around.)
  • Clinically Possible ALS: Upper and lower motor neuron findings in one region or lower motor neuron findings above upper motor neuron findings”

Treatment/ Management

Maintaining functioning and symptom management is the mainstay of treatment for patients with ALS. Physiotherapy involvement is often necessary to maintain mobility and delay atrophy. Often Occupation Therapist involvement is necessary for the provision of home-aids, assistance devices, wheelchairs/ frames. Nutritional support is necessary and often involves the placement of a PEG tube for feeding.

Owing to respiratory failure patients often require the use of non-invasive ventilation/ tracheotomy. These interventions require careful consideration by the patient and family, as they ultimately do not delay the progression of ALS. Patients may elect for palliative/ hospice care.

Drug Treatment

Riluzole is the only drug currently approved for use with ALS patients. It is a glutamate release inhibitor and works by preventing motor neuron death as a result of glutamate build-up. The affect on survival is modest, approximately an additional 3 months.

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