The reflexes

Introduction
A reflex is a predictable reaction to a standardised stimulus. When examining the reflexes, the patient’s cooperation is less essential than when examining sensory and motor function. It is also possible to examine the reflexes of patients with impaired consciousness. The reflexes can be divided into three groups.

1. The proprioceptive or deep tendon reflexes.
   The standardised stimulus causes a rapid stretching of the tendon. Stretching receptors (muscle spindles) are stretched and send a stimulus via a peripheral nerve and posterior nerve root (afferent pathway of the reflex arc) to the anterior horn cell. This then sends a stimulus to the muscle, via the anterior nerve root and peripheral nerve (efferent pathway of the reflex arc), resulting in muscle contraction [Figure 76] (monosynaptic reflex).
2. The superficial or cutaneous reflexes.
   In contrast to the reflexes described above, these reflexes are polysynaptic. This means that several cells are connected between the cell that transmits the afferent stimulus and the anterior horn cell. The standardised stimulus is a tactile stimulus across a predefined area of skin.
   For examination purposes, an important distinction between deep tendon and superficial reflexes is that the deep tendon reflex will be amplified when the patient’s attention is distracted, whereas the superficial reflex will not. In the case of a central or peripheral condition, these reflexes are absent.
3. The primitive reflexes.
   With these reflexes, the standardised stimulus will only result in muscle contractions if there is a lesion in the nervous system. Any reflex that is normally only seen in newborns, but which disappears later one, is known as a primitive reflex.

Figure 76

General comments about the examination technique
If a reflex cannot be elicited, it does not necessarily indicate the presence of pathology, but could be due to a faulty examination technique or the patient being insufficiently relaxed. Each time you test a reflex, your starting position and that of your patient is of utmost importance: the relevant muscle must be completely relaxed. Strike with a loose wrist, making sure you do not grasp the reflex hammer tightly. The tendon / muscle should respond with a rapid and forceful contraction, which is clearly visible or palpable.
The reflex hammer should not be too light.

• There are a number of ways in which the reflex can be made more visible. Deep tendon reflexes are more pronounced if the patient is distracted. To achieve this, ask the patient to count or calculate a sum. Another method used specifically to evoke leg reflexes is the Jendrassik manoeuvre:
  • Ask the patient hook the fingers of both hands together.
  • Just before you strike with the hammer, ask the patient to pull the hooked hands apart. You can also ask the patient to cough at the moment that you strike the reflex.
• To make a proper estimate of the strength of the reflex and any left / right differences, it is important to also feel the reflex muscle contraction. This is achieved by placing the hand on the muscle which will contract, or by holding the limb which will move in response to the reflex.
• Assessment of a reflex should always be based on several measurements, never just one.
• Immediately compare left and right whenever possible.

Reflex tests – the sitting patient
Including:

• Biceps tendon reflex
• Triceps tendon reflex
• Brachioradialis reflex
• Patellar reflex
• Achilles tendon reflex

Reflex tests – the supine patient
Including:

• Biceps tendon reflex
• Triceps tendeon reflex
• Brachioradialis reflex
• Mayer’s reflex
• Hoffmann reflex
• Abdominal reflex
• Patellar reflex
• Achilles tendon reflex
• Plantar reflex

Interpretation

Deep-tendon or proprioceptive reflexes are not always easy to elicit. Even if you have mastered the technique well and the patient is relaxed, there can be large individual differences. The usual gradation for deep tendon reflexes ranges from 0 to 4: 0 = absent reflex
1 = feeble reflex
2 = normal reflex
3 = brisk reflex
4 = brisk reflex with clonus (a clonus is a series of short, rhythmical contractions)
sometimes a fifth possibility is listed:
5 = brisk reflex with sustained clonus Abnormal findings

• Areflexia. This can be caused by:
  • a lesion involving the peripheral nerve (afferent and / or efferent pathway of the reflex arc)
  • a lesion in the central part (spinal root) of the reflex arc (for example, syringomyelia)
  • the acute stage of a spinal cord injury
  • deep coma
  • congenital areflexia, usually involving the legs.
• Sustained clonus is pathological and indicates a lesion in the central motor neuron (CMN) above the reflex’s spinal root. In newborns and people with very quick reflexes a clonus lasting 3 to 4 beats is sometimes found bilaterally.
• Clear and reproducible left / right differences may indicate peripheral nerve damage on the side of the impaired, low reflex or may indicate a lesion involving the CMN (also known as a pyramidal tract lesion) on the side of the brisk reflex. In general it is easy to differentiate between the two by examining the muscle tone and sensory function, amongst other things. Look out for differences between arms and legs as well.

Superficial reflexes are not graded. Only an absent or reduced superficial reflex has any clinical significance. Clear asymmetry is almost always pathological. This can indicate either a CMN lesion or a lesion in the afferent or efferent part of the reflex arc (= peripheral nerve). Interpretation of the plantar reflex and primitive reflexes are explained in the section describing the relevant procedure.