Biceps Weakness in Cervical Stenosis with Radiculopathy
The biceps weakness in this 62-year-old woman is caused by compression of the C5 or C6 nerve root from cervical stenosis, resulting in motor dysfunction along the affected nerve root distribution. 1, 2
Pathophysiologic Mechanism
The weakness develops through two primary mechanisms:
- Mechanical compression of the C5 or C6 nerve root in the neural foramen from degenerative changes including facet joint hypertrophy, uncovertebral joint hypertrophy, disc bulging or herniation, and degenerative spondylosis 1, 3
- Inflammatory cytokines released from damaged intervertebral discs that contribute to nerve root dysfunction even beyond direct mechanical compression 3
Specific Anatomic Correlation
The biceps muscle receives innervation primarily from the C5-C6 nerve roots:
- C5 radiculopathy typically causes weakness in shoulder abduction and elbow flexion (biceps), often with diminished biceps reflex 4, 5
- C6 radiculopathy causes weakness in elbow flexion (biceps) and wrist extension, with diminished brachioradialis reflex 5, 6
- The motor deficit follows the myotomal distribution of the compressed nerve root, while sensory changes follow the dermatomal pattern 1, 2
Critical Distinction: Radiculopathy vs. Myelopathy
This distinction is essential because it determines urgency and treatment approach:
- Pure radiculopathy presents with arm pain, sensory loss, motor weakness (like biceps weakness), and reflex changes in a specific nerve root distribution without gait disturbance 1, 4
- Myelopathy indicates spinal cord compression and presents with gait and balance difficulties, which requires urgent surgical attention and cannot be managed conservatively 7
- If this patient has only biceps weakness with arm symptoms but no gait disturbance, she has radiculopathy; if she has gait problems, she has myelopathy requiring immediate surgical referral 7
Diagnostic Confirmation
Physical examination findings that confirm the diagnosis:
- Spurling test (neck extension with rotation and axial compression toward the symptomatic side) reproduces radicular pain 4
- Diminished deep tendon reflexes, particularly biceps or brachioradialis reflexes, are the most common neurologic findings 4
- Shoulder abduction test (relief of symptoms with arm abduction and hand placed on head) suggests nerve root compression 4
- Motor testing of biceps strength (elbow flexion against resistance) quantifies the degree of weakness 5
Common Pitfall to Avoid
Do not assume MRI findings correlate with symptoms—degenerative changes and nerve root compression are highly prevalent in asymptomatic individuals over 30 years of age, so imaging abnormalities must match the clinical presentation 1, 4. The patient's specific pattern of weakness, sensory changes, and reflex loss must anatomically correspond to the level of stenosis seen on imaging 3, 2.
When Imaging Is Indicated
MRI is not immediately required unless:
- Red flag symptoms are present: trauma, malignancy, prior neck surgery, spinal cord injury, systemic disease, suspected infection, IV drug use, intractable pain, vertebral body tenderness, or progressive neurological deficits 1
- Symptoms persist beyond 4-6 weeks of conservative treatment 4, 3
- Significant motor weakness is present that may indicate need for surgical intervention 3, 5