BCR Negative and Spinal Shock
The absence of the bulbocavernosus reflex (BCR) is a classic sign of spinal shock, not a B-cell receptor finding. The term "BCR negative" in the context of spine trauma refers to the bulbocavernosus reflex being absent, which indicates the patient is still in the acute phase of spinal shock following spinal cord injury 1, 2.
Understanding Spinal Shock and the Bulbocavernosus Reflex
Spinal shock is the immediate loss of all neurological function below the level of a severe spinal cord injury, characterized by flaccid paralysis, absent reflexes (including BCR), and loss of sensation 1, 3. This represents a temporary suppression of spinal cord function that occurs after sudden injury or transection of the spinal cord 1.
Key Clinical Features of Spinal Shock
- Motor function: Complete flaccid paralysis below the injury level with absent muscle tone 1
- Sensory function: Loss of all sensation below the injury level 1
- Reflexes: Absence of all spinal reflexes, including the bulbocavernosus reflex 2, 4
- Autonomic dysfunction: Loss of autonomic nervous system control, particularly with high-level injuries 1
- Duration: Typically lasts days to weeks, though some symptoms can persist up to 12 weeks 1, 2
The Bulbocavernosus Reflex as a Marker
The bulbocavernosus reflex (BCR) is a polysynaptic reflex that tests the integrity of the S2-S4 spinal segments 4. The return of the BCR has traditionally been used by many clinicians to mark the end of spinal shock, though this definition remains controversial 2.
Pattern of Reflex Recovery
Contrary to older teaching, reflexes do not always follow a predictable caudal-to-rostral pattern of recovery 4. In a prospective study of 50 acute spinal cord injury patients:
- The delayed plantar response (DPR) was typically the first reflex to return, followed by the bulbocavernosus reflex and cremasteric reflex within the first few days 4
- Deep tendon reflexes (ankle and knee jerks) returned later, typically by 1-2 weeks 4
- Less than 8% of subjects had complete absence of all reflexes on the day of injury 4
Clinical Implications and Pitfalls
A critical pitfall is assuming that the absence of reflexes immediately after injury means the patient has a complete spinal cord injury 4. The presence or absence of reflexes on the day of injury has limited prognostic value 4.
Prognostic Significance
The duration of the delayed plantar response (DPR) has stronger prognostic value than the BCR for predicting ambulation 4:
- Patients with a DPR lasting 2 days or longer were not ambulatory at discharge 4
- Ambulatory patients either had no DPR or a DPR lasting only 1 day 4
Essential Assessment During Spinal Shock
When evaluating a patient with suspected spinal shock, the American College of Radiology recommends 5:
- Testing sacral sensation and function, including perianal sensation, rectal tone, and voluntary anal sphincter contraction, as these predict neurological recovery 5
- Performing serial neurological examinations to document any changes in motor strength, sensation, and reflex activity 5
- Using the ASIA Impairment Scale for standardized documentation of neurological deficits 5
Imaging Considerations
MRI is the gold standard for diagnosing spinal cord contusions and soft tissue injuries in acute spinal trauma 6. When a patient presents with neurological deficits suggesting spinal cord injury:
- CT cervical spine without IV contrast is the initial imaging of choice for identifying fractures and bony injuries 7
- MRI should be performed when there is confirmed or suspected spinal cord or nerve root injury to characterize the extent of soft tissue damage, cord compression, and intramedullary hemorrhage 7, 6
The key takeaway is that "BCR negative" means the bulbocavernosus reflex is absent, which is a hallmark finding during the spinal shock phase following acute spinal cord injury, not a laboratory test for B-cell receptors.