Deep Tendon Reflexes
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.
A deep tendon reflex is dependent upon the following:
- an intact sensory nerve
- a functional synapse in the spinal cord
- an intact motor nerve fiber
- the neuromuscular junction
- a competent muscle
These reflexes are not dependent upon higher levels of motor function in the brain and cord.
Hyporeflexia is an absent or diminished response to tapping. It usually indicates a disease that involves one or more of the components of the two-neuron reflex arc itself.
Hyperreflexia refers to hyperactive or repeating (clonic) reflexes. These usually indicate an interruption of corticospinal and other descending pathways that influence the reflex arc due to a suprasegmental lesion, that is, a lesion above the level of the spinal reflex pathways
By convention the deep tendon reflexes are graded as follows:
0 = no response; always abnormal
1+ = a slight but definitely present response; may or may not be normal
2+ = a brisk response; normal
3+ = a very brisk response; may or may not be normal
4+ = a tap elicits a repeating reflex (clonus); always abnormal
Whether the 1 + and 3 + responses are normal depends on what they were previously, that is, the patient’s reflex history; what the other reflexes are; and analysis of associated findings such as muscle tone, muscle strength, or other evidence of disease. Asymmetry of reflexes suggests abnormality
The best position is for the patient to be sitting on the side of the bed or examining table. The Babinski reflex hammer () is very good. Use a brisk but not painful tap. Use your wrist, not your arm, for the action. In an extremity a useful maneuver is to elicit the reflex from several different positions, rapidly shifting the limb and performing the test. Use varying force and note any variance in response.
Note the following features of the reflex response:
- Amount of hammer force necessary to obtain contraction
- Velocity of contraction
- Strength of contraction
- Duration of contraction
- Duration of relaxation phase
- Response of other muscles that were not tested. When a reflex is hyperactive, that muscle often will respond to the testing of a nearby muscle. A good example is reflex activity of a hyperactive biceps or finger reflex when the brachioradialis tendon is tapped. This is termed “overflowing” of a reflex.
Bates, Barbara. 1974. A Guide to Physical Examination. J.B. Lippincott Company, Toronto.
Walker, Kenneth. 1990. Clinical Methods: The history, physical and laboratory examinations: Deep Tendon Reflexes. 3rd Ed. Retrieved August 16, 2010 from http://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=cm&part=A2361.