A reflex is an involuntary, rapid response to a stimulus that does not require conscious thought from the brain. This swift action is mediated by a neural pathway known as the reflex arc, which involves a sensory nerve carrying the signal to the spinal cord and a motor nerve carrying the response signal back to the muscle. The assessment of these deep tendon reflexes (DTRs), often called the muscle stretch reflex, is a foundational element of the neurological physical examination. Evaluating the reflex scale helps clinicians gauge the integrity of this reflex arc, which spans the peripheral nerves, spinal cord segment, and the descending motor pathways from the brain.
The Purpose of Reflex Assessment
Testing deep tendon reflexes provides an objective measure for evaluating the health of the nervous system. The reflex arc includes both sensory and motor components, meaning an abnormal result can point to a problem anywhere along this pathway. Comparing the reflex response from one side of the body to the other is informative, as asymmetry often suggests a neurological issue.
This assessment is crucial for localizing potential damage, helping to distinguish between problems originating in the central nervous system (brain and spinal cord) and those in the peripheral nervous system. By testing specific reflexes, a clinician can pinpoint the level of the spinal cord where the potential lesion resides. Using the standardized scale also allows medical professionals to track the progression of a disease or monitor a patient’s recovery over time.
The Standard Deep Tendon Reflex Grading Scale
The most common method for quantifying deep tendon reflexes is the five-point scale, often referred to as the NINDS Myotatic Reflex Scale. This scale ranges from 0 to 4+, with 2+ generally considered the average or expected response. Clinicians apply this scale to common reflexes like the knee jerk (patellar), ankle jerk (Achilles), and elbow responses (biceps and triceps).
A score of 0 indicates a complete absence of a reflex response, even when reinforcement techniques are used. A grade of 1+ is a diminished response, present but noticeably smaller than average. The grade of 2+ is the average response, signifying a brisk, normal reaction with expected speed and force.
Responses more active than average are categorized as 3+, considered brisker than normal, though this can be a normal finding in hyper-responsive individuals. The highest score, 4+, represents a hyperactive response, frequently accompanied by clonus, which is sustained muscle contraction. The scale provides a reliable framework for communicating findings and tracking changes in a patient’s neurological status.
Interpreting Abnormal Reflex Responses
Abnormal scores fall into two main categories: hyporeflexia and hyperreflexia. Hyporeflexia, represented by scores of 0 or 1+, indicates a decreased or absent reflex response. This finding typically suggests a lesion within the Lower Motor Neuron (LMN) pathway, such as the peripheral nerves or motor neurons in the spinal cord.
Conversely, hyperreflexia, indicated by a score of 3+ or 4+, signifies an overactive or exaggerated reflex. This often points to damage in the Upper Motor Neuron (UMN) pathway, which includes nerve tracts descending from the brain and brainstem. The UMN system normally exerts an inhibitory influence, so damage leads to an unchecked, heightened reflex response. Hyperreflexia is frequently accompanied by increased muscle tone (spasticity) and the presence of clonus.
Other Reflex Assessments Used in Diagnosis
While deep tendon reflexes are the most common assessment, the neurological examination also includes other reflex tests that use different scales or binary results. Pathological reflexes are tested to detect UMN damage. The Babinski sign is a prime example, where stroking the sole of the foot causes the big toe to extend upward and the other toes to fan out.
Primitive reflexes are another category, typically assessed in infants to monitor neurological development, such as the Moro or grasping reflex. Their presence beyond a certain age can indicate developmental issues or diffuse brain damage. These assessments complement the DTR scale by providing additional information about the functional integrity of the nervous system.