Motor Neuron Disease: Signs And Symptoms, Causes, Treatment

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Motor neuron disease is a rare but very serious degenerative neurological condition. Motor neuron diseases are characterized by continuous, uninterrupted, progressive degeneration of corticospinal tracts, anterior horn cells, bulbar motor nuclei, or a combination of these lesions. This medical condition can present different forms of Symptoms, which may include: respiratory muscle weakness, atrophy, etc. Diagnosis requires nerve conduction study, electromyography, and exclusion of other causes through laboratory tests and MRI. Now, let us look into what is known as motor neuron disease in this article, including signs and symptoms, causes, and the possible treatment

Motor Neuron Disease: Types

Motor neuron disease can affect the central nervous system as well as the peripheral nervous system. Usually, the exact etiology is not known, the nomenclature and symptoms vary depending on which part of the motor system is most affected. Motor neuron diseases are divided into upper motor neuron and lower motor neuron diseases. Some disorders, (e.g. amyotrophic lateral sclerosis) have features of both. Motor neuron diseases are more common in men, they appear most often in their fifties. As most types of motor neuron diseases can be inherited, individuals at higher risk factors of developing motor neuron disease should medically be alerted.

Treatment of motor neuron disease

Symptoms of amyotrophic lateral sclerosis and other upper motor neuron diseases.

Upper motor neuron diseases (e.g., primary lateral sclerosis) affect neurons in the motor cortex that extend to the brainstem ( corticobulbar bundle) or spinal cord( corticospinal tracts). Symptoms usually include stiffness, clumsiness, and poorly executed movement, which usually first affect the mouth and or throat, then spread to the link

Lower motor neuron disease affects the ventral wall cell or motor nuclei of cranial nerves or their axonal extension to skeletal muscle. In bulbar palsy, only the motor nuclei of the cranial nerve in the brainstem (bulbar nuclei )  are affected. Patients usually initially have facial paralysis, dysphagia, and dysarthria.

When the ventral horn cells of the spinal nerve ( and not the cranial nerve) are affected, as in spinal muscular atrophy, symptoms usually include muscle weakness wasting fasciculation ( visible muscle contraction), and muscle cramps beginning in a hand, foot, or tongue. Poliomyelitis enteroviral infections that attack ventral horn cells, and post-polio syndrome are also lower motor neuron diseases.

Primary lateral sclerosis

In lateral sclerosis, progressive muscle stiffness of the arm and leg occurs with spasticity and hyperreflexia on examination. Fasciculation and muscle atrophy are atypical in this disorder which predominates in the upper motor neuron. Survival is prolonged because the risk of aspiration and pneumonia is low. Several years must pass to result in total disability. This suggests best for an Individual to always take note of all the manifesting Symptoms that may eventually indicate the occurrence of motor neuron-associated diseases.

Diagnosis of motor neuron disease

Electrophysiological test

MRI of the brain, if no cranial nerve damage of the cervical spine.  An additional test to check for other causes that could be treated. The diagnosis of motor neuron diseases is considered in the face of a progressive, generalized motor deficit without significant sensory abnormalities.

Differential diagnosis

Other disorders that cause muscle weakness should be excluded: 

  • Neuromuscular transmission disorder
  • Various myopathies (noninflammatory or drug-induced)
  • Spinal muscular atrophy ( especially in children)
  • Polymyositis
  • Dermatomyositis
  • Thyroid disorder and adrenal disorder
  • Fluid and electrolytes disorder ( hypokalemia and hypercalcemia hypophosphatemia)
  • Various infections ( e.g syphilis, Lyme disease, hepatitis C)
  • Autoimmune-mediated motor neuropathies
  • Cervical spinal stenosis
  • Behavioral variant of frontotemporal dementia (15 to 20% develop motor neuron disease) 
  • Heavy metal poisoning ( e.g lead, mercury
  • Damage to the first and second motor neurons associated with facial muscle weakness strongly suggests amyotrophic lateral sclerosis.

Treatment of motor neuron disease

  1. Supportive care
  2. Riluzole
  3. Edaravone
  4. The mainstay of treatment for patients with amyotrophic lateral sclerosis is appropriate intervention aimed at treating symptoms
  5. A multidisciplinary approach allows better management of progressive neurological disability

No drug offers substantial clinical benefit in Motor neuron disease. However, riluzole can improve survival to a limited extent (2-3 months) and edaravone can slow the decline in function to some extent.

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The following medication helps reduce symptoms

  • For spasticity- baclofen
  • For cramps- quinine or phenyl hydantoin
  • To decrease salivary secretion, a strong anticholinergic medication ( e.g glycopyrrolate, amitriptyline, benztropine, trihexyphenidyl, transdermal hyoscine, atropine)
  • In the case of pseudobulbar syndrome, amitriptyline, fluvoxamine, or a combination of dextromethorphan, and quinidine) 

In the case of progressive bulbar palsy, surgery to improve swallowing has limited results. Hence it is mostly not recommended or advised.

Causes

Some forms of motor neuron diseases are hereditary, they affect several members of the same family. About 10% of motor neuron disease falls into this category. For example, the first genetic cause of motor neuron disease is the mutation (change) of the gene called superoxide dismutase 1 ( SOD1), categorized as familial. This familial form of the disease affects patients in the same way as other forms of motor neuron disease.

The majority of motor neuron diseases are not inherited, most result from indirect and direct impacts like trauma, and sporting activities. Most significantly, the nonhereditary motor neuron disease manifests as a result of habit and lifestyle. But rarely could it be ascribed to a particular source and the cause of the disease is not known. These nonhereditary, so-called sporadic motor neuron diseases are possibly caused by a combination of genetic changes and the patient’s environment and lifestyle

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Conclusion

Finally, Scientists believe that motor neurons stop working not only because of changes in the cells themselves. But also because of damage in the immediate surroundings of the motor neurons in the body. There is evidence that other cell types present in the nervous system may also play a role, at present there is no cure for motor neuron disease. It is strictly advised that an individual should be very conscious of the signs and symptoms of this medical condition to quickly learn how to prevent the emergence of these disorders. A healthy lifestyle is also encouraged, while an individual should pay closer attention to familial forms of motor neuron disease

Dr. David G Kiely is a distinguished Medical Reviewer and former General Medicine Consultant with a wealth of experience in the field. Dr. Kiely's notable career as a General Medicine Consultant highlights his significant contributions to the medical field.

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