From the Guidelines
Hyperreflexia is primarily caused by disorders affecting the upper motor neurons in the brain and spinal cord, with the main diseases including multiple sclerosis, stroke, amyotrophic lateral sclerosis (ALS), spinal cord injuries, and cerebral palsy, as well as conditions such as hyperthyroidism, anxiety disorders, and neurodegenerative diseases like primary lateral sclerosis, as supported by the most recent evidence 1.
Causes of Hyperreflexia
The following are some of the key diseases and conditions that can lead to hyperreflexia:
- Multiple sclerosis
- Stroke
- Amyotrophic lateral sclerosis (ALS)
- Spinal cord injuries
- Cerebral palsy
- Hyperthyroidism
- Anxiety disorders
- Neurodegenerative diseases like primary lateral sclerosis
- Hepatic encephalopathy, which can cause hyperreflexia in its advanced stages, particularly in cases of hepatic myelopathy 2 ### Mechanism of Hyperreflexia Hyperreflexia occurs due to damage or interference with the inhibitory pathways in the central nervous system that normally regulate reflex responses. When these inhibitory mechanisms are compromised, the reflex arc becomes overactive, resulting in exaggerated responses to stimuli. This happens because upper motor neurons normally provide inhibitory control over lower motor neurons in the spinal cord. When this control is disrupted, the lower motor neurons become hyperexcitable, leading to the characteristic increased reflex response.
Clinical Significance
The presence of hyperreflexia often indicates neurological damage and requires further investigation to determine the underlying cause. Clinically, brisk reflexes are tested using a reflex hammer on tendons, with the knee-jerk (patellar) reflex being commonly examined. In some cases, hyperreflexia can be associated with other symptoms such as muscle rigidity, fever, and autonomic dysfunction, as seen in conditions like neuroleptic malignant syndrome and malignant hyperthermia 3.
From the Research
Diseases Causing Hyperreflexia
Hyperreflexia is a condition characterized by overactive or exaggerated reflexes. The following diseases and conditions can cause hyperreflexia:
- Upper motor neuron lesions, which can result from various conditions such as stroke, spinal cord injury, brain injury, or multiple sclerosis 4, 5, 6
- Neurodegenerative conditions, including Parkinson's disease, progressive supranuclear palsy, corticobasal degeneration, frontotemporal dementia, and parkinsonism linked to chromosome 17 7
- Spinocerebellar ataxia syndromes, which are a group of rare, inherited disorders that affect the cerebellum and spinal cord 7
- Cerebral palsy, a group of permanent disorders that appear in early childhood and affect movement, muscle tone, and coordination 7
Mechanisms Underlying Hyperreflexia
The underlying mechanisms of hyperreflexia involve:
- Disturbed inhibition of spinal reflexes following upper motor neuron dysfunction 6
- Hyperexcitability of spinal reflexes, such as stretch reflexes and flexor withdrawal reflexes 8
- Failure of reciprocal inhibition, leading to spastic co-contraction 8
- Increased intrinsic excitability of alpha motor neurons 8
Clinical Presentation
Hyperreflexia can manifest as: