Physiology, Deep Tendon Reflexes

Excerpt

First described in 1875 by Wilhelm Heinrich Erb and Carl Friedrich Otto Westphal, the deep tendon reflex (DTR) is essential in examining and diagnosing neurologic disease. Deep tendon reflexes or, more accurately, the 'muscle stretch reflex' can aid in evaluating neurologic disease affecting afferent nerves, spinal cord synaptic connections, motor nerves, and descending motor pathways. Proper technique and interpretation of results are crucial in achieving a proper distinction between upper and lower motor neuron pathologic processes such as multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), spinal cord injuries, and spinal muscular atrophies, with the presence of hyporeflexia or hyperreflexia considered a 'hard sign' of neurologic dysfunction.

There are five primary deep tendon reflexes: biceps, brachioradialis, triceps, patellar, and ankle.

Biceps Reflex

1. Muscle involved: biceps brachii

2. Nerve supply: musculocutaneous

3. Segmental innervation: C5-C6

Brachioradialis Reflex

1. Muscle involved: brachioradialis

2. Nerve supply: radial

3. Segmental innervation: C5-C6

Triceps Reflex

1. Muscle involved: triceps brachii

2. Nerve supply: radial

3. Segmental innervation: C7-C8

Patellar Reflex (knee-jerk)

1. Muscle involved: quadriceps femoris

2. Nerve supply: femoral

3. Segmental innervation: L2-L4

Achilles Reflex (ankle-jerk)

1. Muscles involved: gastrocnemius, soleus

2. Nerve supply: tibial

3. Segmental innervation: S1-S2

To provide a standard scale for evaluating deep tendon reflexes, in 1993, the National Institute of Neurological Disorders and Stroke (NINDS) proposed a grading scale from 0 to 4. This scale has been validated and is universally accepted.

NINDS grading of deep tendon reflexes.

1. 0: Reflex absent

2. 1: Reflex small, less than normal, includes a trace response or a response brought out only with reinforcement

3. 2: Reflex in the lower half of a normal range

4. 3: Reflex in the upper half of a normal range

5. 4: Reflex enhanced, more than normal, includes clonus if present, which optionally can be noted in an added verbal description of the reflex

In some instances, a plus sign (+) is written after the number. When discussing DTRs, adding or omitting a plus sign does not change the meaning of the reflex grade observed.

What is 'normal' typically depends on the patient's history and past documented reflex grade. Abnormality is suggested when asymmetric reflexes are found. Once the examiner obtains a reflex on one side, they should test the same reflex on the opposite side for comparison.