The abbreviation DTR stands for Deep Tendon Reflexes, which are involuntary muscle contractions triggered by a sudden stretch of the tendon. This physical test is a fundamental part of a standard neurological examination. Checking these reflexes provides quick, non-invasive insight into the functional integrity of the patient’s nervous system, helping practitioners evaluate whether the nerve pathways are functioning correctly.
The Reflex Arc Biological Basis
The deep tendon reflex is an automatic response mediated by a simple neural pathway called the reflex arc. The process begins when the tendon is tapped, stretching the associated muscle. Specialized sensory receptors called muscle spindles detect this change, generating a signal that travels along an afferent (sensory) neuron to the spinal cord. This sensory neuron directly connects (synapses) with an alpha motor neuron, which transmits an efferent (motor) impulse back to the muscle, causing it to contract. This pathway, involving only one sensory and one motor neuron with a single synapse, is known as a monosynaptic reflex arc.
Deep Tendon Reflex Testing Procedures
Healthcare providers use a reflex hammer to elicit the response by delivering a quick, focused tap to the tendon. The patient must be relaxed, as muscle tension can suppress the reflex. If a reflex is difficult to obtain, the examiner may use reinforcement, such as asking the patient to clench their teeth, which distracts the patient and enhances the response.
Common sites tested include:
- The biceps, triceps, and brachioradialis in the arms.
- The patellar (knee-jerk) reflex.
- The Achilles (ankle) reflex.
The resulting muscle contraction is graded on a standardized scale ranging from 0 to 4, with 2+ considered the normal, average response. A score of 0 indicates an absent reflex, while 1+ represents a diminished response. Conversely, 3+ is brisker than average, and 4+ indicates a very brisk response that may include clonus (a rhythmic, repeating muscle contraction). Comparison between the left and right sides of the body is often the most informative part of the examination.
Interpreting Abnormal DTR Results
Deviations from the normal 2+ score are categorized as hyporeflexia or hyperreflexia, providing clues about the location of a potential neurological issue. Hyporeflexia (0 or 1+ score) suggests a problem with the reflex arc itself. This diminished response points toward damage in the peripheral nervous system, involving the sensory neuron, motor neuron, neuromuscular junction, or muscle tissue.
This damage is associated with issues in the lower motor neuron (LMN) pathway. Conditions such as peripheral neuropathy, nerve root compression, or muscle diseases can lead to hyporeflexia.
In contrast, hyperreflexia (3+ or 4+ score) suggests an issue higher up in the central nervous system. This overly brisk response occurs when inhibitory signals that normally travel down from the brain are interrupted. These descending pathways, known as the upper motor neurons (UMN), modulate the reflex. When a lesion occurs in the UMN pathway (e.g., in the brain or spinal cord above the reflex arc), the reflex becomes disinhibited and exaggerated. Hyperreflexia, especially with clonus, is a sign of an upper motor neuron syndrome and can be seen in conditions like stroke, multiple sclerosis, or spinal cord injury.