Superficial (Cutaneous) Reflexes

The superficial reflexes are motor responses evoked by stimulation of the skin rather than by stretch of a muscle, and they differ from the deep tendon reflexes in both their physiology and their clinical behavior. Whereas the muscle stretch reflex is a short, monosynaptic arc, each superficial reflex is a polysynaptic response that travels from cutaneous afferents through a chain of interneurons before reaching the anterior horn cell. Its integrity depends upon three elements acting together: intact cutaneous sensation, an intact spinal segmental arc, and intact descending corticospinal facilitation. Because the cortex facilitates rather than restrains these responses, the consequence at the bedside is the reverse of what is seen with the tendon reflexes. An upper motor neuron lesion, which releases and exaggerates the deep tendon reflexes, instead diminishes or abolishes the superficial reflexes. This single principle explains nearly all of their localizing value and is the reason their loss is counted among the signs of corticospinal disease.

Abdominal Reflexes

The superficial abdominal reflexes are elicited with the patient supine and the abdominal wall relaxed. Each of the four quadrants is stroked briskly with a blunt point, such as the wooden end of a cotton applicator or the handle of the reflex hammer, drawn toward the umbilicus. The normal response is a brief contraction of the underlying abdominal musculature that draws the umbilicus toward the stimulated quadrant. The response is best assessed by comparing the four quadrants with one another and the two sides against each other, since a unilateral or segmental loss is more informative than a generalized reduction.

The reflex is organized segmentally: the upper quadrants are subserved by T8–T9, the level of the umbilicus by T9–T10, and the lower quadrants by T11–T12. Two patterns of loss carry meaning. First, the reflexes are abolished below the level of a spinal cord lesion, so that a sharp transition from preserved upper to absent lower abdominal reflexes can help mark the segmental level of a myelopathy. Second, because the arc depends upon descending corticospinal facilitation, the abdominal reflexes are lost in upper motor neuron lesions situated above the relevant segment, irrespective of the cause. They are characteristically and often symmetrically absent in multiple sclerosis, in which their early loss is a recognized finding.

An important caveat tempers their interpretation. The superficial abdominal reflexes are frequently and harmlessly absent in the obese, the multiparous, the elderly, and those who have undergone abdominal surgery, in whom a lax or scarred abdominal wall prevents a visible response. Their absence is therefore meaningful chiefly when it is asymmetric or segmental; a symmetric bilateral absence in a patient with a pendulous or surgically altered abdomen should not, by itself, be read as a sign of disease.

Cremasteric Reflex

The cremasteric reflex is elicited by stroking the skin of the medial thigh in a downward direction. The normal response is contraction of the cremaster muscle with prompt elevation of the ipsilateral testis. The arc enters the cord through afferents at L1 and returns through efferents at L2, carried by the genitofemoral nerve. Like the abdominal reflexes, it is depressed by lesions of its own segmental arc (L1–L2) and by upper motor neuron lesions above that level.

Beyond its localizing role, the cremasteric reflex has a specific clinical application in the assessment of the acute scrotum. Its absence is a recognized feature of testicular torsion, in which the reflex is characteristically lost on the affected side; a preserved cremasteric reflex makes torsion less likely, although it does not exclude it. The sign should be interpreted alongside the remainder of the examination and is unreliable in young infants, in whom the reflex is normally not well developed.

Plantar Response

The plantar response is obtained by drawing a blunt point along the lateral border of the sole, from the heel toward the metatarsophalangeal joints and then medially across the ball of the foot. The normal response is plantarflexion (downward curling) of the toes. This flexor response is the cutaneous reflex of the foot and the expected finding in the intact adult.

The abnormal counterpart, in which the great toe dorsiflexes (extends) with fanning of the lateral toes, is the extensor plantar response, or Babinski sign. This is not a diminished superficial reflex but a pathologic reflex in its own right, signifying corticospinal tract dysfunction, and it is treated in detail on its own pages along with its reinforcing maneuvers. It is noted here only to complete the account of the normal flexor plantar response and to distinguish the two phenomena.

Bulbocavernosus and Anal Reflexes

The sacral reflexes test the integrity of the lowest segments of the cord and its outflow and are indispensable in the evaluation of the conus medullaris, the cauda equina, and the state of spinal shock. Both depend upon an arc at S2–S4.

The anal reflex (anal wink) is elicited by lightly scratching or pricking the perianal skin, which produces a visible reflex contraction of the external anal sphincter. The bulbocavernosus reflex is elicited by squeezing the glans penis or the clitoris, or by gently tugging an indwelling urinary catheter, which produces reflex contraction of the external anal sphincter palpable on rectal examination. Loss of these reflexes points to disruption of the sacral arc, as in a conus medullaris or cauda equina lesion. In the setting of acute spinal cord injury, the bulbocavernosus reflex has a further use: its return marks the end of spinal shock, after which the completeness of any cord lesion can be reliably assessed.

Summary of the Superficial Reflexes