Deep Tendon Reflexes (DTRs):
In a normal person, when a muscle tendon is tapped briskly, the muscle immediately contracts due to a two-neuron reflex arc involving the spinal or brainstem segment that innervates the muscle. The afferent neuron whose cell body lies in a dorsal root ganglion innervates the muscle or Golgi tendon organ associated with the muscles; the efferent neuron is an alpha motoneuron in the anterior horn of the cord. The cerebral cortex and a number of brainstem nuclei exert influence over the sensory input of the muscle spindles by means of the gamma motoneurons that are located in the anterior horn; these neurons supply a set of muscle fibers that control the length of the muscle spindle itself.
Deep Tendon Reflexes:
Check the deep tendon reflexes using impulses from a reflex hammer to stretch the muscle and tendon. The limbs should be in a relaxed and symmetric position, since these factors can influence reflex amplitude. As in muscle strength testing, it is important to compare each reflex immediately with its contralateral counterpart so that any asymmetries can be detected. If you cannot elicit a reflex, you can sometimes bring it out by certain reinforcement procedures. For example, have the patient gently contract the muscle being tested by raising the limb very slightly, or have them concentrate on forcefully contracting a different muscle group just at the moment when the reflex is tested. When reflexes are very brisk, clonus is sometimes seen. This is a repetitive vibratory contraction of the muscle that occurs in response to muscle and tendon stretch. Deep tendon reflexes are often rated according to the following scale:
- 0: absent reflex
- 1+: trace, or seen only with reinforcement
- 2+: normal
- 3+: brisk
- 4+: nonsustained clonus (i.e., repetitive vibratory movements)
- 5+: sustained clonus
Deep tendon reflexes are normal if they are 1+, 2+, or 3+ unless they are asymmetric or there is a dramatic difference between the arms and the legs. Reflexes rated as 0, 4+, or 5+ are usually considered abnormal. In addition to clonus, other signs of hyperreflexia include spreading of reflexes to other muscles not directly being tested and crossed adduction of the opposite leg when the medial aspect of the knee is tapped.
References for Deep Tendon reflexes:
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