Deep tendon reflexes are involuntary muscle contractions that occur when a specific tendon is stretched. Doctors commonly test these reflexes using a reflex hammer, gently tapping specific points on the body like the knee, elbow, or ankle. The muscle connected to the tapped tendon quickly stretches, activating sensory receptors within the muscle. These receptors send a signal along nerves to the spinal cord, which then sends a rapid return signal to the same muscle, causing it to contract. This automatic process helps medical professionals assess the condition of the nervous system.
The Reflex Grading Scale
Clinicians use a standardized 5-point scale to grade deep tendon reflex responses, providing a consistent way to document and interpret findings. A grade of 0 indicates no reflex response. A 1+ grade signifies a diminished or hypoactive reflex, a slight response less than typical.
A 2+ reflex is considered normal or average, representing a brisk and expected response. When a reflex is brisker than average, it receives a 3+ grade, indicating an increased response. The highest grade, 4+, denotes a very brisk, hyperactive reflex, often accompanied by clonus. Clonus refers to a series of involuntary, rhythmic muscle contractions that occur after the initial reflex.
Significance of Decreased Reflexes
When deep tendon reflexes are diminished or absent (grade 0 or 1+), this is known as hyporeflexia. Hyporeflexia points to a problem within the peripheral nervous system, which includes nerves extending from the spinal cord to the muscles and limbs. This issue is a “lower motor neuron” problem, indicating damage to nerve roots or peripheral nerves.
Various conditions can lead to decreased reflexes. For instance, peripheral neuropathy, a form of nerve damage often seen with diabetes, can impair reflex responses. Other causes include muscle diseases like muscular dystrophy, or a pinched nerve in the spine, which can disrupt the reflex pathway. Nerve injuries can also reduce reflexes.
Significance of Increased Reflexes
Conversely, brisk or exaggerated deep tendon reflexes (grade 3+ or 4+) are referred to as hyperreflexia. Hyperreflexia suggests a problem within the central nervous system, specifically involving the brain or spinal cord. This condition is an “upper motor neuron” issue, where normal inhibitory signals from the brain that regulate reflex activity are disrupted.
The lack of this higher-level control allows the reflex arc to become overactive, leading to a more pronounced response. Conditions causing increased reflexes include stroke, which damages brain tissue, or spinal cord injury, which can interrupt descending pathways. Multiple sclerosis, a neurological disorder affecting the brain and spinal cord, can also result in hyperactive reflexes due to demyelination of nerve fibers.