What is Flaccid Paralysis?

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  • Written By: Caitlin Kenney
  • Edited By: Bronwyn Harris
  • Last Modified Date: 08 October 2019
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Flaccid paralysis is a medical condition characterized by extremely weak muscles and deterioration of muscle tone. This loss of muscle function typically results from a disease rather than injury, but is almost always a symptom of damage to the nervous system. This is an abnormal, serious medical situation that requires immediate care from a physician. Treatments depend on the cause of the paralysis and may include surgery, antibiotics, and long-term rehabilitation.

Paralysis, a temporary or permanent loss of muscle function, can apply to one muscle or many muscles in the body, and may be partial, allowing the patient to experience some sensation or control, or complete, in which the patient has no sensation or muscle function in the affected area. Patients with flaccid paralysis may experience sensation, but they lose voluntary control of muscle movements as the muscles weaken due to atrophy, or the dwindling of muscle mass. Though muscle atrophy can occur simply because of a lack of use, people that develop paralysis may be dealing with a deeper problem called neurogenic atrophy. Neurogenic atrophy tends to have a more sudden onset, as it results from damage to the nervous system, rather than prolonged disuse.


Anterior spinal artery syndrome, also known as Beck’s syndrome, is one of the more common causes of flaccid paralysis. The anterior spinal artery is responsible for getting blood to most of the spinal cord, and when it is blocked, as happens in Beck’s syndrome, nerves that control muscle function can fail. This usually has to do with the build-up of plaque in the artery.

Flaccid paralysis can also arise because of a disease affecting the nervous system. Paralytic polio, a potentially fatal virus, causes acute flaccid paralysis (AFP), wherein the patient very suddenly loses reflexes and muscle control. This virus is rare and can almost always be prevented with a polio vaccine. Other viruses, such as encephalitis, can cause similar paralytic effects.

The bacteria responsible for botulism, Clostridium botulinum, can also cause flaccid paralysis and should be treated as a medical emergency. After the bacteria enters the body, either on food or through an open wound, it colonizes and releases toxins that prevent muscle contraction. Foodborne botulism is most common in uncooked canned foods and wound botulism is most prevalent amongst people using intravenous drugs. Paralysis usually starts in the face before moving down to the limbs, and potentially to the respiratory muscles, where it can prove fatal.

Guillain–Barré syndrome (GBS), lower motor neuron lesion, and Reye’s syndrome all include flaccid paralysis in their symptoms, as well. Guillain–Barré syndrome (GBS) is an autoimmune disorder in which the body tries to attack a foreign substance, but attacks its own nerves instead. This disorder only affects peripheral nerves, all nerves outside the brain or spinal cord. A lesion on a lower motor neuron, which connects the muscle cells to the brainstem and spinal cords, can be caused by injury, or by any of the aforementioned maladies.

Reye’s syndrome causes flaccid paralysis at later stages. The exact cause of this syndrome is unknown, though it has been connected with aspirin use in children with viral diseases. Reye’s syndrome is more common in children, and can be fatal.


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