In a spinal cord injury patient with retained rectal sensation, can the bulbocavernosus reflex still be used to assess sacral (S2‑S4) function?

Assessment of Bulbocavernosus Reflex in SCI Patients with Retained Rectal Sensation

Yes, the bulbocavernosus reflex (BCR) remains clinically applicable and should still be tested in spinal cord injury patients with retained rectal sensation, as it provides complementary information about sacral reflex arc integrity and helps distinguish upper motor neuron (UMN) from lower motor neuron (LMN) lesions, which has critical prognostic and therapeutic implications for bladder, bowel, and sexual function.

Why BCR Testing Remains Important

The presence of rectal sensation confirms incomplete injury and indicates some preservation of sensory pathways through the sacral segments. However, this does not eliminate the need for BCR testing because:

• BCR assesses the motor reflex arc (S2-S4 segments via the pudendal nerve), which is functionally distinct from sensory preservation 1
• The reflex status determines whether the lesion is UMN (reflex present, indicating intact spinal reflex arc with loss of supraspinal inhibition) or LMN (reflex absent, indicating disruption of the sacral reflex arc) 1
• This UMN vs LMN distinction directly predicts autonomic function patterns: UMN lesions associate with detrusor and rectum hyperactivity plus reflex erection/ejaculation, while LMN lesions show the opposite pattern 1

Clinical Reasoning Algorithm

When evaluating sacral function in incomplete SCI:

1. Test rectal sensation (S4-S5 dermatomes) - confirms incomplete injury if present
2. Test BCR - squeeze glans penis/clitoris and observe for bulbocavernosus muscle contraction
3. Test anal sphincter reflex (ASR) - perform simultaneously as complementary assessment 2, 3

Interpretation:

• BCR present + rectal sensation present = Incomplete UMN lesion with preserved sacral reflex arc
• BCR absent + rectal sensation present = Incomplete injury with possible LMN component affecting motor reflex arc OR technical difficulty eliciting reflex
• If BCR negative but ASR positive (occurs in 13% of cases) = Confirms reflex arc integrity via different pathway, suggesting BCR negativity is technical rather than true pathway disruption 2

Important Caveats

BCR has notable limitations that clinicians must recognize:

• BCR can be falsely negative in up to 45% of SCI patients, not necessarily indicating pathway disruption but potentially reflecting difficulty eliciting the reflex 2
• BCR can change over time (32% changed status at 45 weeks) without corresponding neurological changes or interventions, suggesting variable ease of elicitation 2
• The reflex arc for BCR may differ from ASR in some patients, explaining discordant results 2

To address these limitations: Always test both BCR and ASR together. If BCR is negative but ASR is positive, the sacral reflex arc is likely intact, and the negative BCR represents technical difficulty rather than true LMN injury 2, 3.

Prognostic Value Beyond Classification

According to the Congress of Neurological Surgeons guidelines, urethral and rectal sphincter function (which BCR helps assess) can predict neurological outcomes in thoracolumbar SCI patients 4. Specifically:

• Voluntary external anal/urethral sphincter contraction correlates significantly with bladder recovery (P < 0.01) 4
• Absence of perineal pinprick sensation predicts poor bladder recovery 4

The BCR provides objective assessment of sphincter reflex function that complements voluntary contraction testing and sensory examination, creating a more complete picture of sacral cord function and recovery potential 1.

Practical Recommendation

In incomplete SCI with retained rectal sensation, perform both BCR and ASR as part of the standard neurological examination. The anal reflex may be tested first as it is less intrusive (using pinprick stimulation of S4-5 dermatome already performed during ISNCSCI examination) 3. However, BCR provides additional valuable information and should not be omitted, particularly when planning bladder, bowel, and sexual function management strategies 5, 1.