Hyporeflexia

What is hyporeflexia?

Hyporeflexia happens when your skeletal muscles have a decreased or absent reflex response. An absent reflex response is also called areflexia.

A reflex is an involuntary (automatic) action your body does in response to something. Reflexes protect your body from things that can harm it.

Hyporeflexia results from any interruption of the reflex arc, which has a sensory part, a central part (spinal cord) and a motor part. Damage to any of the parts (sensory nerves, spinal cord or motor nerves) can potentially cause hyporeflexia. If the damage is to your motor nerves or motor nerve cells, it’s called a lower motor neuron lesion.

Hyporeflexia is the opposite of hyperreflexia, in which your muscles have an overactive response. Damage to the motor neurons that transmit signals from your brain to your spinal cord causes hyperreflexia. This is called an upper motor neuron lesion.

Hyporeflexia is just a physical sign that’s very useful for a neurologist when performing an exam, but it usually doesn’t bother the person experiencing it.

How is hyporeflexia diagnosed?

Healthcare providers use the deep tendon reflex (DTR) examination to check for hyporeflexia or hyperreflexia as part of a neurological exam. The best known of the reflexes is the patellar, or knee-jerk, reflex.

The DTR exam involves a healthcare provider tapping your knee with a rubber hammer (it shouldn’t hurt). This tap stretches your patellar tendon and the muscle in your thigh that connects to it. Normally, your peripheral nerves (more specifically, sensory neurons) then send a signal to your spinal cord that the muscle has been stretched.

Normally, your spinal cord (via motor neurons) very quickly sends a message back to the muscle telling it to contract. The contraction causes your lower leg to kick out. If you have hyporeflexia, your leg will kick only weakly or won’t kick out at all.

For effective and reliable results for the DTR exam, you need to be as relaxed as possible. If you’re thinking about the test or have a rigid posture, the results might not be accurate. Your provider may try to distract you with a question or some other method as they tap on your knee to prevent this.

Aside from your knee, your provider may also check reflexes:

• Along the outside of your elbows.
• In the crooks of your arms.
• At your wrists and ankles.
• At your chin.

What are the causes of hyporeflexia?

Damage anywhere along the reflex arc causes hyporeflexia. These tissues include:

• Sensory nerve fibers.
• Sensory nerve cells or neurons.
• Spinal cord.
• Motor nerve cells or neurons.
• Motor fibers.

Rarely, neurological diseases that affect the connection between nerves and muscles cause hyporeflexia.

Neurological conditions or injuries that can cause hyporeflexia include:

• Peripheral neuropathies: Neuropathy is damage or dysfunction of one or more nerves that typically results in numbness, tingling, muscle weakness and pain in the affected area. Neuropathies frequently start in your hands and feet, but can affect other parts of your body, too. It indicates a problem within your peripheral nervous system.
• Guillain-Barre syndrome: This is a rare autoimmune disease in which your immune system attacks your nerves rapidly over days and causes loss of myelin — the “insulation” of your nerves.
• Chronic inflammatory demyelinating polyneuropathy (CIDP): This is an autoimmune condition that also affects myelin but over a longer period.
• Spinal cord injuries: Accidents such as falls and motor vehicle crashes can cause spine fractures and severe pressure on your spinal cord. This causes paralysis and hyporeflexia early on. However, over time, people often develop hyperreflexia below the level of the spinal cord injury.
• Amyotrophic lateral sclerosis (ALS): ALS, also known as Lou Gehrig’s disease, is a progressive disease of upper and lower motor neuron lesions. In this condition, even though there’s loss of the lower motor neurons, people more often have hyperreflexia than hyporeflexia because of parallel loss of their upper motor neurons.
• Lambert-Eaton myasthenic syndrome (LEMS): This is a rare condition that affects the connection between your nerves and muscles. It’s associated with hyporeflexia and areflexia.

How is hyporeflexia treated?

Treatment for hyporeflexia depends on the underlying cause. The goal of treatment is to treat the underlying condition.

For example, healthcare providers treat Guillain-Barre syndrome either with IV infusions of immunoglobulins (IVIg) or with a procedure in which your plasma is filtered from your blood (plasma exchange).

When should I see a healthcare provider about hyporeflexia?

If your healthcare provider finds hyporeflexia and other symptoms of a serious neurological condition, they may consider referring you to a neurologist. It’s important to remember that reflexes are different for different people, and some people normally have weak reflexes. Most people with weak reflexes and no other neurological difficulty don’t have a neurological disease.

A note from Cleveland Clinic

Hyporeflexia can be a sign of an underlying neurological condition. If you have hyporeflexia, you probably won’t know it until a healthcare provider checks your reflexes. However, hyporeflexia often happens alongside other symptoms, such as muscle weakness, muscle atrophy or imbalance. If you notice an unexplainable decline in your muscle strength and/or have other symptoms, it’s important to see a healthcare provider.