The anal wink is a superficial reflex in which a light scratch or pinprick of the skin around the anus makes the external anal sphincter contract visibly. It tests the S2-S4 segments and the pudendal nerve. It is part of the assessment of the lowest part of the spinal cord and the cauda equina.
| Nerve root | S2-S4 |
|---|---|
| Area | Perianal skin |
| How to test | With the patient lying on one side, the examiner lightly scratches or pricks the perianal skin on each side and watches for a visible contraction of the anal sphincter. |
| Muscles | |
| Nerve Supply | Pudendal nerve (inferior anal nerves) |
Tightens the anal sphincter in response to perianal touch, contributing to continence.
Loss of the anal wink, along with saddle numbness and bladder or bowel symptoms, suggests cauda equina or conus medullaris damage. It is also absent during spinal shock after acute cord injury. It is routinely checked in suspected cauda equina syndrome and spinal cord injury.
Compression of the sacral roots abolishes the anal wink, with saddle anaesthesia and sphincter dysfunction.
A lesion at the tip of the spinal cord damages the S2-S4 segments and abolishes the reflex.
In the first hours to days after acute spinal cord injury, reflexes below the lesion, including the anal wink, can be temporarily absent.
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