Anocutaneous reflex and spinal cord syndromes

[HighB]

There is a question (1693) in UW that had a guy with severe radicular pain + loss of anocutaneous reflex (anal wink) and the answer was cauda equina syndrome. Yes, with the pain clue, it is more likely to be cauda equina syndrome than conus medullaris syndrome.

My question is, is the anal wink reflex also absent in conus medullaris syndrome?
Since both have saddle sensory loss, wouldn't the afferent limb of the reflex be disrupted in both syndromes?

Thank you.

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[Rahas]

Conus medullaris is the terminal portion of the spinal cord, hence a lesion here would, among other things, lead to UMN deficits. This means the anocutaneous reflex should, theoretically, be exaggerated. However I don't see this mentioned, probably because its too difficult to clinically pick it up.

Cauda equina causes a LMN lesion, and, like you said, leads to a/hyporeflexia.

You should associate weakness, tone, and reflexes together since these are all motor effects. Lumping them with numbness, a sensory symptom, is probably what led to the confusion.

 

[HighB]

You should associate weakness, tone, and reflexes together since these are all motor effects. Lumping them with numbness, a sensory symptom, is probably what led to the confusion.

No, I did not confuse sensory symptoms with motor symptoms. My idea was that, since in both syndromes we have a saddle-like sensory loss, wouldn't that disrupt the afferent sensory signal coming from the skin around the anus and that would prevent the efferent motor limb of the reflex from firing?

Stroking of the skin around the anus > afferent sensory signal by S2-4 > spinal cord > efferent motor signal by S4 > anal wink

If patient can't sense the skin in that area, no afferent signal would be generated, right? In that case, wouldn't both syndromes include loss of this reflex?

 

[Rahas]

You're absolutely correct, for some reason I never gave enough attention to realize the afferent limb was initiated by cutaneous sensation rather than a tendon being stretched (doh!). I just looked at uptodate and emedicine, and they dont specifically talk about this.

I think if sensation goes, this reflex goes, so it might be a non specific sign of damage anywhere along the reflex arc, which includes both syndromes. That said, conus medullaris tends to be symmetrical, whereas cauda equina can be asymmetrical / unilateral. If thats the case, I guess the anal wink might be preserved on one side in cauda equina. Conus medullaris causes saddle or perianal anesthesia relatively consistently I believe, while I think cauda equina symptoms depend a lot on which nerve roots are involved.

 

[Rahas]

Uptodate on conus medullaris:

Lesions at vertebral level L2 often affect the conus medullaris. There is early and prominent sphincter dysfunction with flaccid paralysis of the bladder and rectum, impotence, and saddle (S3-S5) anesthesia.

And on cauda equina:

Sensory loss of all sensory modalities occurs in the dermatomal distribution of the affected nerve roots


These two syndromes are a pain to easily find information on for some reason.

 

[HighB]

These two syndromes are a pain to easily find information on for some reason.

Exactly!

Thank you for the answers, Rahas.