Reflexes are rapid, involuntary muscle contractions occurring in response to a sudden external stimulus. This process involves a simple two-neuron arc within the nervous system, bypassing the brain for speed. Clinicians use the assessment of deep tendon reflexes (DTRs) as a quick, non-invasive method to evaluate the integrity of the peripheral and central nervous systems. Charting these findings using a standard grading system is necessary to accurately communicate the patient’s neurological status across different healthcare providers.
Understanding the Standard Grading System
The universally accepted method for documenting DTR responses is the 0 to 4+ scale, often referred to as the National Institute of Neurological Disorders and Stroke (NINDS) Myotatic Reflex Scale. This system provides a consistent, numerical language for describing the reflex response observed. A grade of 2+ represents the normal or average response, where the muscle contraction is brisk but controlled, corresponding to a healthy, balanced reflex arc.
Charting begins by assigning a numerical grade to the reflex elicited from a specific tendon. A grade of 0 signifies an absent reflex, where no muscle response is detected even after using reinforcement techniques. A 1+ grade denotes a diminished or hypoactive reflex, indicating a trace response that is less than the expected normal average.
Moving toward the higher end of the scale, 3+ describes a response that is brisker than average, sometimes referred to as hyperreflexia. This response may still be considered normal if it is generalized and symmetric. The highest grade, 4+, indicates a markedly hyperactive reflex that is often accompanied by clonus, which is a rhythmic, involuntary oscillation of the muscle. When charting, this number is recorded next to the specific muscle tested, such as “Achilles: 2+” or “Patellar: 4+.”
Proper Technique for Eliciting Deep Tendon Reflexes
Eliciting an accurate reflex requires the patient to be completely relaxed, as muscle tension can diminish the response. The appropriate limb must be positioned and supported to ensure the muscle is at a mid-range length, allowing for a maximal stretch when the tendon is struck. For example, when testing the patellar reflex, the patient should be seated with their legs dangling freely, or the examiner can support the knees in a partially flexed position.
The reflex hammer should be held loosely, allowing it to swing freely with a wrist motion, letting the hammer’s weight deliver a quick, controlled tap. The strike must be directed precisely onto the tendon itself, not the muscle belly, to abruptly stretch the muscle spindle and trigger the reflex arc. For the patellar reflex, the target is the tendon just below the kneecap.
When testing the Achilles reflex, the patient’s foot is gently dorsiflexed to pre-stretch the tendon, and the strike is delivered just above the heel. If a reflex response is diminished (0 or 1+), a reinforcement maneuver can be employed to enhance the response. The Jendrassik maneuver involves the patient locking their fingers together and pulling just as the tendon is struck, providing a distraction that reduces inhibitory signals from the brain.
Interpreting the Results
The numerical grade assigned to a reflex response gains its true meaning when interpreted in the context of the entire nervous system examination. A low grade, specifically 0 or 1+ hyporeflexia, often suggests a problem within the two-neuron reflex arc, such as a Lower Motor Neuron (LMN) lesion. This pathology can involve the nerve root, peripheral nerve, or anterior horn cells in the spinal cord, disrupting the pathway that mediates the muscle stretch.
Conversely, hyperreflexia (grades 3+ or 4+) is associated with an Upper Motor Neuron (UMN) lesion. This indicates damage to the descending pathways from the brain or spinal cord, which normally exert inhibitory control over the reflex arc. The removal of this inhibition results in an exaggerated response to the tendon tap.
The most severe form of hyperreflexia (4+ grade) is the presence of clonus, defined as a series of rhythmic, involuntary muscle contractions following a rapid stretch. Clonus is a sign of central nervous system dysfunction. Comparison between corresponding reflexes on the right and left sides of the body is often more informative than the absolute number, as asymmetry suggests a focal neurological issue.