Anal reflex

Anal reflex, also known as the anal wink or anal wink reflex, is a reflex that involves the contraction of the external anal sphincter upon stroking of the skin around the anus. This reflex is an important component of the physical examination, particularly in the neurological assessment of patients.

Mechanism

The anal reflex is mediated by the sacral segments of the spinal cord (S2-S4). It is a somatic reflex that involves sensory input from the perianal skin traveling via the pudendal nerve to the sacral spinal cord, and motor output from the sacral spinal cord to the external anal sphincter via the pudendal nerve. The integrity of this reflex arc is essential for the maintenance of fecal continence.

Clinical Significance

The presence of the anal reflex is an important sign of normal lower spinal cord function. Its absence may indicate damage to the sacral spinal cord or the nerves that supply the anal area, such as in cases of spinal cord injury, cauda equina syndrome, or severe peripheral neuropathy. Additionally, an absent or diminished reflex may be seen in patients with diabetes mellitus due to diabetic neuropathy.

In the context of neurological examination, the anal reflex is assessed along with other sacral reflexes to evaluate the integrity of the sacral spinal cord. This assessment is particularly relevant in patients with suspected spinal cord lesions or in the evaluation of patients with bowel and bladder dysfunction.

Procedure

To elicit the anal reflex, the examiner gently strokes the skin around the anus with a blunt instrument, such as a cotton swab. A normal response is the contraction of the external anal sphincter, observed as a twitch or wink of the anus. The reflex should be tested bilaterally, and the response should be symmetrical.

Importance in Neonates

In neonates, the anal reflex is also assessed as part of the routine neurological examination. Its presence in newborns is a reassuring sign, indicating normal spinal cord function at the sacral level. Absence of the reflex in a newborn may necessitate further neurological evaluation.

See Also

• Bulbocavernosus reflex
• Cremasteric reflex
• Reflex arc