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Hyporeflexia

What Is It, Causes, Important Facts, and More

Author: Ashley Mauldin, MSN, APRN, FNP-BC

Editors: Ahaana Singh, Lisa Miklush, PhD, RN, CNS

Illustrator: Jillian Dunbar

Modified: 3 Jan 2024

What is hyporeflexia?

Hyporeflexia refers to a condition in which the muscles have a decreased or absent reflex response. This is in contrast to hyperreflexia, in which there is an overactive response of the muscles. 

What causes hyporeflexia?

Hyporeflexia is usually the result of damage to the motor neurons in the central nervous system. Motor neurons are responsible for transmitting signals from the brain to the rest of the body to produce muscle movement. Damage or changes to the motor neurons, also known as motor neuron lesions, can be caused by underlying central nervous system disorders like spinal muscular atrophy, Guillain-Barre syndrome, chronic inflammatory demyelinating polyneuropathy (CIPD), amyotrophic lateral sclerosis (ALS), and spinal cord injuries. In addition, damage can be caused by hypothyroidism, which results from low levels of thyroid hormones. The associated damage to the motor neurons that send messages between the spine and the rest of the body are known as lower motor neuron lesions and result in hyporeflexia. In contrast, damage to the motor neurons that send signals from the brain to the spine are known as upper motor neuron lesions and can produce hyperreflexia.

What are the signs and symptoms of hyporeflexia?

Signs and symptoms of hyporeflexia usually appear gradually and include muscle weakness that can increase over time. At first, an individual with hyporeflexia may only notice a slight decrease in muscle strength; over time, however, they may have difficulty holding objects, walking, and standing up straight. Additionally, individuals may experience muscle atrophy. 

Other signs and symptoms may present depending on the underlying cause. Individuals with ALS often also experience slurred speech, difficulty walking, and, eventually, difficulty breathing. Those with Guillain-Barre syndrome usually present with a rapid onset numbness and paralysis of the arms, legs, face, and breathing muscles. CIDP often presents with weakness as well as numbness and tingling in the arms and legs, and can eventually progress to a complete loss of normal muscle reflexes. Finally, with hypothyroidism, individuals may also experience fatigue, changes to body temperature, constipation, dry skin, weight gain, slowed heart rate, as well as pain and stiffness in the muscles and joints. 

Is hyporeflexia a sign of MS?

Hyporeflexia is not a sign of multiple sclerosis, commonly known as MS. Instead, MS usually presents with hyperreflexia, as well as spasticity of the muscles which results in unusual tightness of the muscles due to prolonged muscular contraction. 

How do you diagnose hyporeflexia?

Diagnosing hyporeflexia is aimed at determining the underlying cause. A physical examination may be performed, as well as a test of the deep tendon reflexes. A reflex hammer can be used to test the deep tendon reflexes in various muscles, including the bicep muscle of the arm. Normally, the bicep muscle will immediately contract. With hyporeflexia, there will be a delayed response and it will take longer for the muscle to contract. 

In addition, blood tests, nerve conduction studies, magnetic resonance imaging (MRI), and muscle biopsies may be required. A diagnostic test called electromyography may also be used to evaluate the muscle response and the electrical activity of the muscles.

How do you treat hyporeflexia?

Treatment of hyporeflexia depends on the underlying cause and is aimed at improving and maintaining muscle strength. In cases of spinal muscular atrophy, medications may be prescribed to improve muscle movement and strength. With CIDP and Guillain-Barre syndrome, treatment with steroids can help to reduce the inflammation causing the muscle weakness. In cases of spinal cord injury or hypothyroidism, the injury or condition usually needs to be treated in order to resolve the hyporeflexia. Finally, ALS currently has no treatments that can stop the progression of the condition. 

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