Reflex Testing

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There are three types of reflexes

  1. Muscle stretch reflexes: myotatic and inverse myotatic
  2. Cutaneous reflexes
  3. Primitive reflexes

The reflexes tested during examination come about due to brisk stretch of the muscle, leading to activation of the muscle spindles. They are often called deep tendon reflexes but this is a misnomer. The Golgi tendons located within the organs have the opposite effect causing relaxation of muscle called the inverse myotatic reflex. This is not tested during examination, but occurs with sudden extreme stretch to the tendon.

Muscle Stretch Reflexes

Grading

NINDS Muscle Stretch Reflex Scale
Grade Finding
0 Reflex absent despite reinforcement
1 Reflex small, less than normal; includes a trace response or a response brought out only with reinforcement
2 Reflex in lower half of normal range
3 Reflex in upper half of normal range
4 Reflex enhanced, more than normal; includes clonus if present, which optionally can be noted in an added verbal description of the reflex

Reflexes can be reinforced by the Jendrassik manoeuvre. "Hook together the flexed fingers of his right and left hands and pull them apart as strongly as possible" while eliciting the reflex.

Clinical Significance

Disease at different locations in the nervous system causes different findings

  • Disease at peripheral nerve or spinal segment: reduced or abolished reflex (lower motor neuron response)
  • Disease along the descending corticospinal pathway: exaggerated reflex (upper motor neuron response)
  • Disease of the spinal cord: abolishes the reflex at the level of the lesion (lower motor neuron response), and exaggerates all reflexes from spinal levels below the level of the lesion (upper motor neuron response)

Absent or exaggerated reflexes are only relevant when one of the following is true

  1. The absent reflex is present along with other lower motor neuron signs such as weakness, atrophy, fasciculations.
  2. The exaggerated reflex is present along with other upper motor neuron signs such as weakness, spasticity, Babinski or Hoffman sign.
  3. The reflexes are asymmetric which either means that the side with the reduced reflex amplitude has a lower motor neuron lesion or the side with the higher amplitude has an upper motor neuron lesion.
  4. The exaggerated reflex is unusually brisk compared to a more proximal spinal segmental level reflex. This suggests spinal cord disease between the two segments.

Absent reflexes also have localising value in radiculopathies.

Localising Value of Diminished Reflexes in Radiculopathies[1]
Radiculopathy Absent Reflex +LR
C6 Biceps or Brachioradialis 14.2
C7 Triceps 3
L3 or L4 Quadriceps 8.5
L5 Hamstring 6.2
S1 Achilles 2.7

Cutaneous Reflexes

Superficial Abdominal Reflex

The superficial abdominal reflex tests T6-T11. The skin of the abdomen is stroked which causes the underlying abdominal wall muscle to contract. One abdominal quadrant is tested at a time. The skin can be stroked lateral to medial or medial to lateral.

This reflex is reduced in both upper and lower motor neuron disease, however they are absent in 20% of normal patients and in the elderly. it is also common to have asymmetric reflexes or reflexes only preserved in the upper quadrants in normal individuals.

Bulvocavernosus Reflex

In lithotomy, apply sudden manual compression to the glans penis or clitoris, feeling for reflex contraction of the bulbocavernosus muscle and external anal sphincter. The reflex contraction is felt by palpating the skin behind the scrotum or per rectum. Percussing the suprapubic area or pulling the balloon of an inflated Foley catheter can also cause the reflex.

This reflex tests the conus medullaris and the S2-4 spinal nerves. Its absence has a +LR in women of 2.7, and +LR in men of 13.

See Also

References

  1. โ†‘ McGee, Steven R. Evidence-based physical diagnosis. Philadelphia, PA: Elsevier, 2018.